diseases quetions

Learn Basic Concepts of Parasitology

1. What is parasitism?

Parasitism is an inharmonious interspecific ecological interaction in which individuals of a species (the parasites) explore organs, tissues or cells of individuals of another species (the hosts) causing harm to these.

2. What is the difference between ectoparasite and endoparasite?

Ectoparasites are parasites that explore the external surface of the host (like, for example, mites that parasite the skin). Endoparasites are parasites that live within the body of the host (like the taenias).

Image Diversity: ectoparasite endoparasite

3. Concerning the number of hosts how are parasites classified?

Parasites that require only one host are called monoxenous parasites. Parasites that need more than one host for their life cycle are called heteroxenous parasites.

4. What is the criterion used to classify hosts as intermediate hosts or as definitive hosts?

The criterion used to classify hosts as intermediate hosts or as definitive hosts is the kind of reproduction of the parasite, sexual or asexual, withinthe host. The host within which the sexual reproduction stage of the parasite occurs is the definitive host. The host within which the asexual reproduction stage of the parasite occurs is the intermediate host.

5. What are vectors of parasites?

Vectors of a parasite are organisms able to transport the parasite during stages of its life cycle mediating the infection of other hosts. For example, the mosquito Aedes aegypti is the vector of the dengue virus; triatomine bugs are vectors of the Trypanosoma cruzi, protozoan that causes Chagas’ disease; mice are vectors of leptospira, bacteria that cause leptospirosis.

Image Diversity: vectors of disease

6. What is an etiological agent of disease?

An etiological agent of disease is the agent that causes the disease. It may be a living being, substance or environmental fact.

7. What is the difference between the concepts of epidemic disease and endemic disease?

Endemic diseases are those that often affect people of a given place, many or few individuals. Epidemic diseases are those of rapid spread and elevated number of new cases. An endemic disease can turn into an epidemic disease.

Study the Bacterial Infections Here

1. What are some human diseases caused by bacteria and what are their respective modes of transmission?

The main human bacterial infections transmitted by respiratory secretions (sneezes, cough) and saliva drops are: bacterial pneumonias, tuberculosis, whooping cough (pertussis), diphtheria, bacterial meningitis. Main bacterial diseases transmitted by blood or sexual contact are: gonorrhea, syphilis. Main bacterial diseases transmitted by animal vectors are: bubonic plague, endemic typhus, leptospirosis. Some bacterial diseases transmitted through fecal-oral route and contaminated food are: cholera, typhoid fever. Other important bacterial infections: Hansen's disease, possibly transmitted by saliva drops and contact with injured skin and mucosae; trachoma, eye disease transmitted by ocular secretions; tetanus, transmitted when the etiological agent enters the body through skin wounds.

Bacterial Infection - Image Diversity: bacteria

2. What is tuberculosis? How is the disease transmitted? Is there treatment for tuberculosis?

Tuberculosis is a disease caused by the Mycobacterium tuberculosis, bacteria which attack other organs of the body but mainly the lungs leading to respiratory insufficiency. Before 1940, tuberculosis had already been one of the main causes of death in the USA and Europe. The disease can remain latent, without manifestation for several years and even throughout the life.

Tuberculosis is highly contagious, transmitted by air route through sneezes and coughs from a person with the active disease. Transmission is common between members of the same family or even in work environments. The disease today has treatment with efficient antibiotics. Generally, the patient receives three different drugs for several months until healing is complete. There are however some strains of multiresistant TB bacteria that emerged by mutation and natural selection due to the intense use of antibiotic drugs mainly in hospitals and treatment facilities; in these cases the treatment is more difficult.

Bacterial Infection - Image Diversity: tuberculosis

3. Is there vaccine against tuberculosis?

The vaccine against tuberculosis is called BCG (bacillus Calmette-Guérin). BCG is not used in some countries where tuberculosis is not so prevalent because it can distort later diagnostic studies of the disease; in other countries, like Brazil, it is obligatory for children. The vaccine is made of attenuated TB bacteria.

4. Are all pneumonias caused by bacteria?

Pneumonia is the generic name of inflammation of the lungs. Besides bacterial pneumonias, there are pneumonias caused by virus, fungi, toxic pneumonias, etc.

Bacterial Infection - Image Diversity: pneumonia

5. What is Hansen’s disease (etiological agent, mode of transmission, clinical manifestations and prevention)?

The etiological agent of Hansen’s disease is bacteria called Mycobacterium leprae. The mode of transmission is not yet totally known but it is believed that respiratory secretions and saliva drops can spread the disease. Hansen’s disease is a chronic disease (slow progression) that generally attacks the skin and the peripheral nerves although other areas of the body can be affected. In the skin nodules, reddish spots, thickening of the dermis and lack of sensitivity appear; the mucosae, especially the nasal mucosa, may be injured and also the viscera may be affected. The main form of prevention is information, since there is available treatment; infected people should, as soon as possible, look for health services for evaluation and treatment of the disease.

In the past Hansen’s disease was called leprosy.

Bacterial Infection - Image Diversity: Hansen's disease

6. What is the etiological agent and the main manifestations of cholera?

Cholera is a bacterial disease caused by the Vibrio cholerae. The disease is transmitted by fecal-oral route and the main mode of transmission is ingestion of contaminated water or food. It is most prevalent in places that lack adequate sanitary conditions.

Inside the human gut the cholera vibrion releases toxins called enterotoxins. The infection can cause intense diarrhea, vomiting, dehydration and even death in more severe cases.

Bacterial Infection - Image Diversity: cholera

7. What is meningitis?

Meningitis is the generic name given to inflammation of the meninges, membranes that cover the central nervous system. Meningitis can have several causes (infectious, toxic, traumatic, neoplastic infestation, autoimmune). Bacterial infections caused by meningococcus, haemophilus, pneumococcus or by tuberculosis bacteria are severe and contagious.

The main symptoms of bacterial meningitis are high fever, nuchal rigidity, intense headache, vomiting and sometimes convulsions. The disease should be treated with antibiotics.

Bacterial Disease - Image Diversity: meningitis

8. What is syphilis?

Syphilis, also known as lues, is a disease caused by the bacteria Treponema pallidum. Before the discovery of penicillin, syphilis was a fatal disease. Today the use of antibiotics can cure the disease completely. Patients with primary syphilis present a single and painless wound in the skin, sometimes called chancre, in the region where the treponema has penetrated; the chancre is highly infective. Syphilis is one of the main STDs, sexually transmitted diseases. Generally the chancre develops in the penis, vagina, anus, hands or mouth, and the bacteria is often transmitted by sexual contact. Later syphilis develops into systemic diseases, secondary and tertiary syphilis.

Syphilis can also be transmitted by blood transfusions, accidents with contaminated objects and vertically from the mother to the child (congenital syphilis). It is very important for patients with the disease to seek treatment as soon as possible and to undergo tests to look for other STDs, like HPV and HIV infections.

9. What is an antibiogram?

Antibiogram is a laboratory test intended to guide the choice of adequate antibiotic to treat a given bacterial infection. In the antibiogram cultures of bacteria obtained from tissues contaminated by the infection under study are submitted to the action of different antibiotics. After some time it is verified which of the antibiotics were successful in interrupting the bacterial growth or in killing the bacterial population.

The antibiogram is very important to avoid exaggerated and inefficient use of antibiotics and the emergence of multiresistant bacteria.

Bacterial Infection - Image Diversity: antibiogram

Learn the Protozoan Diseases

1. Which is the kingdom of the parasites that cause malaria and Chagas’ disease?

Those diseases are caused by the protozoans, beings of the kingdom Protista.

2. What is the scientific name of the etiological agent of Chagas’ disease?

The etiological agent of Chagas’ disease is the Trypanosoma cruzi. The name “cruzi” was given in honor of the Brazilian doctor Oswaldo Cruz. The disease was named after the Brazilian doctor Carlos Chagas.

3. Under which forms is the Trypanosoma cruzi found in its hosts?

In the definitive hosts as well as in triatomine bugs (intermediate hosts) the protozoan that causes Chagas’ disease alternates mastigote (flagellate) and amastigote forms and also intermediate forms between these forms.

4. What is the vector of Chagas’ disease? How is the disease transmitted?

The vector of Chagas’ disease is its intermediate host, a triatomine bug. The main species is Triatoma infestans.

Hemipteran insects, like triatiomines, have sucking mouthparts that can be used to suck blood from animals or organic fluids from plants. The vectors of Chagas’ disease are hematophagous hemipterans that have nocturnal habits. The blood-sucking bugs become infected when they bite a contaminated person. The parasites then multiply within the bug gut and are eliminated with its feces. When a contaminated triatomine bites another person it defecates near the bite site and the released protozoans can penetrate into the definitive host through mucosae or through the bite wound. Wild and domestic mammals can also be vessels forthe disease.

5. What is the life cycle of Trypanosoma cruzi?

Trypanosoma cruzi is a heteroxenous parasite, i.e., it has an intermediate host, the triatomine bug, and a definitive host, the human. The triatomine bug becomes infected by sucking the blood of a contaminated person. Within the bug gut the protozoan reproduces itself. When the triatomine bites another person it defecates near the bite site. Generally the bitten person itches the area of the bite and the parasite gains the circulation of the definitive host. Within humans theTrypanosoma cruzi multiply as amastigote form in the cardiac muscle tissue or in the nervous tissue forming pseudocysts. These pseudocysts break releasing flagellate parasites into the circulation and the cycle is repeated.

Image Diversity: trypanosome life cycle triatomine

6. What is the incubation period of an infection?

Incubation period is the time interval between the infection by an agent that causes disease and the first signs or symptoms of the disease.

7. What is the average incubation period of Chagas’ disease? What are some signs and symptoms of the acute phase of Chagas’ disease?

Chagas’ disease may or may not present an acute phase. When it is present, the incubation period is about 5 to 14 days. The chronic phase, however, can manifest in more than 10 years after the infection.

At the site where the trypanosoma has penetrated the skin or the mucosa becomes swelled: This sign is known as chagoma. Another sign that may appear in up to 20% of cases after the infection is the Romana’s sign, a swelling of one of the eyelids when infection took place through the ocular route. In the acute Chagas’ disease fever, malaise, inflammation and enlargement of lymph nodes may occur. In more severe cases fatal inflammation of the cardiac muscle or of the meninges may happen.

8. In the long term which are the organs affected by chronic Chagas’ disease?

In the chronic phase of Chagas’ disease, that manifests years after the infection, the trypanosoma infests the muscles of the heart causing insufficient blood pumping, pulmonary edema and increase in the size of the organ (cardiomegaly). This is the cardiac manifestation of Chagas’ disease. The main symptoms that appear are dyspnea, cough and cardiac arrhythmias.

In the digestive form of manifestation of the disease the parasite destroys cells of the autonomic nervous system responsible for the peristaltism of the digestive tube. Since the motility of the esophagus and intestines is reduced the transit of materials inside these organs is impaired and they increase in size (width), conditions respectively known as megaesophagus and megacolon. The main symptoms are dysphagia (impaired swallowing), constipation, flatulence and formation of fecaloma (accumulation of feces inside the bowels).

9. What is prophylaxis?

Prophylaxis are measures taken to prevent diseases. For example, the use of condoms in sexual relations is a prophylaxis against contamination by agents that cause STDs (sexually transmitted diseases).

10. What are the etiological agents of malaria?

The etiological agents of malaria are protozoans of the genus Plasmodium. There are four different types of plasmodia that cause malaria: Plasmodium malariae, Plasmodium vivax, Plasmodium falciparum and Plasmodium ovale.

11. What are the human tissues affected by malaria? What are the main clinical manifestations of the disease?

The plasmodium infects the human blood causing destruction of red blood cells and it also affects the liver. Malaria characterizes by periodical episodes of fever, chills and sweating that can be accompanied by headache, nausea, vomiting and jaundice. The destruction of red blood cells may lead to anemia and hypoxemia.

The infection by Plasmodium falciparum if not treated can cause other complications and even death.

12. What is the vector of malaria? How different is its behavior from the behavior of the vector of dengue fever?

The vector of malaria is a mosquito of the genus Anopheles, also called anopheline. In opposition to the mosquito vector of the dengue fever, the anopheline has nocturnal habits.

Image Diversity: Anopheles

13. What are the intermediate and the definitive hosts of the plasmodium?

In the life cycle of the plasmodium humans are the intermediate hosts (where asexual reproduction takes place) and the vector mosquito is the definitive host (where sexual reproduction occurs).

14. What is the life cycle of Plasmodium vivax?

The vector mosquito bites a contaminated person and ingests female and male gametocytes of the parasite. Within the insect gut the gametocytes differentiate into gametes and fecundation occurs, forming zygotes. Each plasmodium zygote by mitosis (sporogony) generates numerous infective sporozoites that migrate to the salivary glands of the mosquito. When the mosquito bites a person the sporozoites enter the human circulation and when in the liver they undergo the first asexual reproduction (tissue schizogony), releasing several merozoites into the blood. The merozoites infect red blood cells where the second asexual reproduction of the cycle (erythrocytic schizogony) and the production of many other parasites occur; some of these parasites differentiate into gametocytes. The red blood cells then break (hemolysis), the parasites are released in the blood and the cycle can restart.

Image Diversity: plasmodium life cycle

15. To which phase of the plasmodium life cycle do the typical chills and fever of malaria correspond?

The typical chills and fever episodes of malaria correspond to the phase when red blood cells are destroyed after the erythrocytic schizogony of the plasmodium life cycle.

16. What are the main prophylactic measures against malaria?

The main preventive measures against malaria are the elimination of the vector mosquito, treatment of infected people, avoidance of the mosquito bite, information for travelers to endemic areas and the use of preventive medicines.

17. What are other important human diseases caused by protozoans?

Some other important protozoan infections are amebiasis, giardiasis, trichomoniasis, leishmaniasis, toxoplasmosis and meningoencephalitis by free-living amoebas.

18. What is the etiological agent of amebiasis? How is it transmitted and what are the typical manifestations of the disease?

Amebiasis is caused by the protozoan Entamoeba histolytica, or simply amoeba.

The transmission of the disease is oral-fecal, through contaminated water and food or by insects like cockroaches and flies. The amoeba parasites the intestine of humans generally in an asymptomatic manner, but it can sometimes cause enteritis with diarrhea and severe dysentery, abdominal pain, weight loss and anemia. In rare cases extra-intestinal invasion may occur affecting the liver, skin, genital organs and other organs.

Image Diversity: Entamoeba histolytica

19. What is the parasite that causes giardiasis? How is it transmitted and what are the typical manifestations of the disease?

Giardiasis is a protozoal infection caused by Giardia lamblia, or simply giardia, a flagellate protozoan.

The transmission is fecal-oral, through contaminated water and food or carried by insects like cockroaches and flies. Giardiasis manifests like amebiasis, as an enteritis with diarrhea, abdominal pain, weight loss and anemia.

20. What is trichomoniasis? Why is it classified as an STD?

Trichomoniasis is an extra-intestinal protozoan infection caused by Trichomonas vaginalis, a flagellate protozoan. The parasite infects the urinary tract of males and females. In females it causes discharge, pain and itching.

Trichomoniasis is an STD because its main mode of transmission is sexual contact.

21. What are the main manifestations of leishmaniasis?

There are two main forms of leishmaniasis: cutaneous leishmaniasis and visceral leishmaniasis (also known as kala-azar). The form is determined by the species of infective leishmania and by the immune response of the host.

Image Diversity: leishmaniasis

22. What is the etiological agent of cutaneous leishmaniasis? How is the disease transmitted and what are its typical manifestations?

The etiological agent of cutaneous leishmaniasis is the protozoan Leishmania braziliensis.

The transmission, like in the visceral form of the disease, is by the bite of the sand fly Lutzomya (named after the Brazilian scientist Adolfo Lutz), the vector host. Cutaneous leshmaniasis develops in the bite site where the parasite establishes itself. The skin wound has a volcanic crater shape, a reddish injury with elevated borders. From the primary lesions the parasites can spread through the blood to affect other areas, mainly the mucosae of the nose, mouth and pharynx, causing facial deformations.

23. What is the etiological agent of visceral leishmaniasis? How is the disease transmitted and what are its typical manifestations?

Visceral leishmaniasis is caused by the protozoan Leishmania donovani.

The transmission is similar to the cutaneous leishmaniasis, by the bite of sand flies. The affected organs generally are the liver, the spleen and the bone marrow. The patient often has fever, weight loss, splenomegaly (hypertrophy of the spleen), anemia and decreased counts of leukocytes and platelets. The disease may cause death.

24. What is the parasite that causes toxoplasmosis? How is the disease transmitted and what are its typical manifestations?

Toxoplasmosis is caused by the protozoan Toxoplasma gondii, a sporozoan.

Toxoplasmosis is a disease transmitted by cats, which are the definitive hosts of the parasite. Cats eliminate toxoplasma oocysts in feces; the oocysts are extremely resistant and remain viable for months in the environment. Human beings are infected when ingesting water or food contaminated by oocysts or when making contact with contaminated objects. Humans can also become infected by eating meat of animals like pork, cow and sheep, which can be intermediate hosts too. Vertical transmission, from mother to offspring, may also occur.

In toxoplasmosis the cystic form of the parasite invades tissues of the body, including the brain and the retina. The infestation is potentially fatal. In congenital toxoplasmosis the child may present blindness and mental retardation. The disease is especially severe when occurring as an opportunistic disease in AIDS patients.

Image Diversity: Toxoplasma gondii

Know the Basics About Fungal Infection

1. What are the main human diseases caused by fungi?

The main human diseases caused by fungi in immunocompetent patients are coccidioidomycosis, histoplasmosis, blastomycosis, paracoccidioidomycosis, or South American blastomycosis, sporotrichosis and onychomycosis (nail mycosis).

In immuno-deficient patients, besides the diseases mentioned above, other fungal diseases like systemic candidiasis, aspergillosis, cryptococcosis and other opportunistic diseases can occur.

2. Moniliasis is one of the most common opportunistic diseases in AIDS. What is the etiological agent of moniliasis and what is the other name of the disease? Why is monilia also common in healthy newborns?

The etiological agent of moniliasis is Candida albicans, a fungus. Moniliasis is also known as mucocutaneous candidiasis. In AIDS moniliasis can complicate and turn into systemic candidiasis, affecting many organs.

Newborns do not yet have their immune system working with complete efficiency and thus they are more susceptible to candidiasis that generally appears in mouth and in the genital mucosae and disappears naturally.

Image Diversity: moniliasis

3. What are some fungal diseases transmitted by animal feces?

Bat and pigeon feces can carry Histoplasma capsulatum, the fungus agent of histoplasmosis. The infection is transmitted through inhalation of contaminated dust in places visited by these animals (caves, tunnels, squares, roofs, etc.). Cryptococcosis is another fungal disease transmitted by pigeon excrement.

4. What are some antibiotics used against fungi?

The topical or systemic azoles (like itraconazole, fluconazole and others), amphotericin B, the echinocandins (caspofungin, micafungin), terbinafine and griseofulvin are examples of antifungal drugs.

Learn the Main Viral Infections Here

1. What are some human diseases caused by virus and what are their respective modes of transmission?

The main viral diseases transmitted by respiratory secretions (sneezes, cough) and by saliva drops are flu, mumps, smallpox (variola, already considered eradicated), rubella, measles, SARS. Main viral diseases transmitted through blood or sexual contact are AIDS, hepatitis B, hepatitis C, HPV, ebola hemorrhagic fever. Main viral diseases transmitted by animal vectors are rabies, dengue fever, yellow fever. Some viral diseases transmitted by fecal-oral route, including contaminated food, are hepatitis A, poliomyelitis (disease almost eradicated in many parts of the world).

2. What is the virus that causes flu? Why doesn't the body produce permanent immunity against that virus? How does the vaccine against flu work?

Flu is a disease caused by the influenza virus, a highly mutant DNA virus. Due to the high mutation rate of the virus, that forms many different strains, flu always presents epidemic features in affected populations and people may have several flu episodes during life (the immune response made from previous infections is not efficient in future infections).

The vaccine against flu is a vaccine made of attenuated virus of three different strains. Each year the WHO (World Health Organization) researches and determines which are the strains that should compose the vaccine. This is a strategy to face the high mutation rate of the virus.

Viral Infection - Image Diversity: influenza virus virus mutation

3. Why is rubella during gestation a threat to the fetus?

If occurring during gestation rubella is a dangerous disease because the virus crosses the placenta and contaminates the fetus. The fetus then develops congenital rubella, a teratogenic (cause of malformations) disease.

Congenital rubella may be prevented by vaccination. Doctor must always be consulted before vaccination.

4. What are the main available vaccines against poliomyelitis?

The vaccines used against poliomyelitis are the Sabin vaccine and the Salk vaccine. The Sabin vaccine contains attenuated virus and is taken through oral drops. The Salk vaccine is made of dead virus and is administered by injection.

5. Is rabies caused by virus or by bacteria? How is it transmitted? Which organs and tissues are affected by the disease? How is it prevented and treated?

Rabies, also known as hydrophobia, is a viral disease. It is found in dogs, cats, bats and other wild mammals. The transmission to humans occurs through the saliva of contaminated animals, mainly through bites.

The rabies virus is neurotropic and attacks the central nervous system in a fast and lethal fashion. The prevention of the disease is done by prophylactic vaccination of animals and humans. The treatment is done by anti-rabies serum containing specific antibodies against the virus.

6. What is the difference between smallpox (variola) and measles?

Smallpox is a viral infection like measles. Smallpox is transmitted by respiratory secretions, saliva and objects in contact with contaminated patients. The disease is characterized by the appearance of numerous vesicles on the skin of the face, trunk and limbs, that can suppurate and form crusts; smallpox complications can lead to death. Measles is transmitted by saliva drops and respiratory secretions too. It is characterized by exanthems (red spots on the skin), fever, malaise and lymphadenomegaly (enlarged lymphnodes). If not treated measles complications can cause death.

Smallpox killed thousands of people around the world in the end of the 19th century and the beginning of the 20th century but today it is almost eradicated by vaccination. Nowadays however a great fear is the possibility of use of smallpox virus in biological weapons and by bioterrorists. Measles is not eradicated and affects millions of people each year. Both diseases can be prevented by vaccination.

7. What are the three main types of viral hepatitis?

There are many types of viral hepatitis. The most important epidemiologically are hepatitis A, hepatitis B and hepatitis C.

Viral Infection - Image Diversity: hepatitis virus

8. What are the modes of transmission, main signs and symptoms and treatments of hepatitis A?

Hepatitis A is an acute disease of low mortality caused by the hepatitis A virus (an RNA virus). It is transmitted by fecal-oral route often through contamination of foods like vegetables and sea-food. The virus attacks the liver and its incubation period varies between 15 and 45 days. After incubation the symptoms are fever, headache, abdominal pain, malaise, nausea and vomiting and the main signs are jaundice, hepatomegaly (enlargement of the liver) and darkened urine (due to excessive bile in blood). Blood tests show increased levels of hepatic enzymes caused by injuries to liver cells. Hepatitis A often heals naturally after 4 to 6 weeks.

9. What are the modes of transmission, main signs and symptoms and treatments of hepatitis B?

Hepatitis B is a disease caused by a DNA virus. The transmission is by blood (wounds, sexual relations, transfusions, accidents with contaminated material, etc.). The most common form of the disease is chronic, the infected patient carries the virus for life and the liver gradually suffers injuries that can lead to cirrhosis or even to hepatic cancer. Another form of the disease is acute, sometimes fulminating, with symptoms similar to those of hepatitis A but more severe and sometimes lethal. There are persons that are asymptomatic carriers of the virus. The level of hepatic injury is assessed by blood tests of hepatic enzymes and by hepatic biopsy (extraction of small samples of tissue to be examined under the microscope). Viral replication can be estimated through PCR (polymerase chain reaction).

10. What are the modes of transmission, main signs and symptoms and treatments of hepatitis C?

Hepatitis C is caused by an RNA virus and transmitted through blood (like hepatitis B, through wounds, sexual relations, transfusions, accidents with contaminated material, etc.). The usual manifestation is chronic and many people that have the virus are asymptomatic. The liver gradually undergoes injuries and some patients evolve to cirrhosis,hepatic cancer and death. Today interferon use is an attempt to control replication of the hepatitis C virus. The assessment of the disease is made periodically by hepatic biopsy and by blood tests of hepatic enzymes. Viral replication can be estimated through PCR (polymerase chain reaction).

11. Are there non viral hepatitides?

Hepatitis is a generic name for inflammation of the liver. There are bacterial hepatitides, for example, in lepstopirosis, and toxic hepatitides, for example by alcohol, medicines or inhaled chemical products.

12. What are the main human viral diseases transmitted by mosquitoes?

The main human viral infections transmitted by mosquitoes are dengue fever and yellow fever.

13. What is dengue?

Dengue, or dengue fever, is an epidemic disease in some countries (for example, in Brazil), and its most dangerous form is hemorrhagic dengue. It is caused by four different but related viruses, the reason that it is difficult for an already infected person to become immunized against the disease. Dengue is prevalent in tropical and subtropical regions of Asia, Africa and South America and it is transmitted by the bite of the Aedes aegypti mosquito, a diurnal mosquito. The viral infection causes varied symptoms similar to flu, like fever, malaise, myalgia (muscle pain); in hemorrhagic dengue high fever, with or without convulsions, and hemorrhages may occur leading to circulatory failure and death. There is no vaccine against dengue since there are four agent viruses and it is supposed that the severity of the disease is greater when the patient is already protected against one type of virus and is infected by another. The best prophylactic method is to eliminate the vector mosquito.

Viral Infection - Image Diversity: Aedes aegypti

14. What is yellow fever?

Yellow fever is a viral infection that occurs mainly in Central Africa and in the Amazon region of South America. It is prevented through vaccination and transmitted by many species of mosquitoes of the Aedes genus, including Aedes aegypti e Haemogogus. The infection causes clinical manifestations that range from asymptomatic cases to lethal fulminating cases. Generally the disease begins with fever, chills, malaise, headache, nausea and evolves to jaundice (increase of bilirubin in blood, after which the disease is named), mucosal and internal hemorrhages, hemorrhagic vomiting and renal failure.

Prevention is done by regular mass vaccination and vaccination of travelers to endemic areas. The combat against the vector mosquito is also an important prophylactic measure.

15. Why is it difficult to produce efficient vaccines against a viral infection like dengue and AIDS?

It is difficult to make vaccines against dengue because there are four different types of viruses that cause the disease (DEN1, DEN2, DEN3 and DEN4) and it is supposed that the protection against one of them aggravates the clinical manifestation when the person is later infected by the another dengue virus.

In the case of HIV, the production of a vaccine is difficult because the virus is highly mutant and evades the antibody action.

16. Is a viral infection treated with the same kind of drug that treats bacterial infections?

Antibacterial drugs, potent against a great variety of bacteria, are not effective against viruses, which are intracellular parasites. A viral infection is difficult to treat since anti-viral drugs are too specific and have limited efficiency. In general the anti-viral drugs reduce the viral load (number of virus) relieving symptoms.

The anti-virals (and anti-retrovirals, drugs that act against RNA virals) often inhibit the action of specific enzymes that participate in the virus life cycle.

AIDS - Q&A Review

1. How is HIV transmitted? What is the disease caused by this virus?

HIV (human immunodeficiency virus) is supposed to be transmitted through blood, semen, vaginal secretions and maternal milk.

HIV is the virus that causes AIDS (acquired immune deficiency syndrome), a disease characterized by destruction of cells of the immune system making the body susceptible to many opportunistic and severe diseases.

Image Diversity: HIV

2. Which type of virus is the HIV? What is the enzyme reverse transcriptase present in HIV?

HIV is a retrovirus, i.e., an RNA viral (its genetic material is RNA and not DNA).

Reverse transcriptase is a specific enzyme of the retrovirus responsible for the transcription of the viral RNA into DNA within the infected (host) cell. This DNA then commands the production of viral proteins and the viral replication.

Image Diversity: reverse transcriptase

3. What are CD4 lymphocytes? What is the relationship between these cells and HIV? How does HIV replicate?

CD4 lymphocytes are T helper lymphocytes that present in their plasma membrane receptor proteins called CD4.

CD4 lymphocytes are the cells that HIV infects and within which the virus replicates. HIV has proteins in its capsule that bind to the CD4 receptors of lymphocytes. Through that bond the virus fuses with the cell membrane and its content (RNA, reverse transcriptase, protease, etc.) penetrates into the cytoplasm and the viral replication process begins.

HIV RNA is then converted into DNA by the reverse transcriptase. The new DNA is inserted into the genetic material of the lymphocyte with the aid of enzymes called integrases. By transcription and translation this DNA commands the synthesis of proteins necessary for the assemblage of new viruses. Long polypeptides are thus produced and then fragmented into proteins and viral enzymes by the enzyme protease. So new HIV viruses are assembled and break the cell membrane to gain the circulation.

Image Diversity: CD4 lymphocytes HIV life cycle

4. Why is AIDS difficult to prevent by vaccination?

It is difficult to produce a vaccine against AIDS because the HIV is a highly mutant virus. In almost every replication the produced viruses have different proteins in their surface making difficult their recognition bythe immune system.

5. What is the cause of the immunodeficiency presented by AIDS patients?

The cause of the immunodeficiency presented by AIDS patients is the destruction of CD4 T helper lymphocytes by the HIV. With this destructionthe immune system becomes impaired and the body cannot defend itself against many diseases that normally do not develop in immunocompetent people.

6. What is the difference between carriers of HIV and AIDS patients?

A person can be a carrier of the HIV without necessarily being affected by the immunodeficiency syndrome at that time since the virus can remain in the body for many years without producing clinical manifestations. The AIDS condition is characterized when the patient actually becomes immunodeficient and begins to show signs and symptoms of opportunistic diseases.

7. How does the CD4 counting act to monitor the HIV infection? What is another laboratory method to follow up the disease?

The CD4 counting test is done from a blood sample of a person infected by the HIV. In this test the number of CD4 cells is counted. If that number (concentration) is abnormally low it means immunodeficiency and the patient usually must be treated with antiretroviral drugs. The other test used to follow up the infection is the viral load test. In this test the number of HIV virus is estimated from a blood sample indicating whether the treatment (control) of the disease has been successful or not.

8. What are the main opportunistic diseases that can affect AIDS patients?

Among the opportunistic diseases that affect HIV infected people during the AIDS stage some are: mucocutaneous and systemic candidiasis, Kaposi’s sarcoma (blood vessel tumors that result in darkened spots on the skin and internal organs), tuberculosis, cytomegalovirus infection, pneumonia by the fungus P. Carinii (pneumocystis pneumonia), toxoplamosis, herpes, etc. Some other opportunistic diseases are: salmonellosis, histoplasmosis, aspergillosis, cryptococcosis, isosporiasis, lymphomas.

9. How long is the incubation period of the HIV? What is meant by acute AIDS?

The incubation period of the HIV (the time interval between the infection and the beginning of the immunodeficiency symptoms) ranges in average from 10 to 15 years.

Acute AIDS is the clinical situation characterized by signs and symptoms that may appear in 5 to 30 days after the infection by the HIV, due to the high replication rate ofthe virus on this period. Acute AIDS does not always happen and many times it is mistaken for common diseases like the common cold. The patient can present fever, malaise, myalgia (muscle pain) and arthralgia (joint pain), lymphadenomegaly (enlargement of lymphnodes), sweating and diarrhea. The manifestation often lasts from 3 to 15 days.

10. What are the three phases into which the HIV infection is often divided?

The HIV infection is often divided into three phases: the acute phase, from the infection to 1 until 9 weeks after the infection, a phase in whichthe virus replicates and the number of CD4 lymphocytes is reduced; the asymptomatic phase, lasting from 9 weeks to often more than 10 years, in which the viral load remains stable and the CD4 count is not abnormally low; the AIDS stage, when the viral load is high, CD4 count is abnormally low and opportunistic diseases manifest.

11. How do antibody-based tests detect how HIV infection works?

After the infection by the HIV the immune system begins the production of antibodies (primary immune response) against the virus. The tests ELISA (enzyme-linked immunosorbent assay) and Western-blot search for the presence of specific antibodies against HIV antigens in blood samples. Since only one positive ELISA is not conclusive, as false positive tests may happen, the Western-blot test is often used after the positive ELISA.

12. What is the window phase of an infection? How is this concept important for the test of HIV infection in blood banks?

The primary immune response of the body facing any infection is not immediate. The window phase is the period from the infection until the formation of detectable specific antibodies against the infective agent. In this period, immunochemical tests that indirectly search infections, like the ELISA and the Western-blot for HIV, give a negative result even if the person is actually infected by the agent. In the case of HIV, the window phase can last about 2 weeks to 3 months.

The window phase is a big problem for blood banks that perform only immunochemical tests on the donated blood. This is the reason why in some countries the blood donors are submitted to a series of questions regarding their prior behavior, mainly sexual and drug use related, in the months preceding the donation and also to voluntary confidential self exclusion, in which they declare whether their blood may be used or should be excluded. Instead of facing this dangerous problem, modern blood banks nowadays use the PCR (polymerase chain reaction) for HIV, a test that is not distorted by the window phase since it is not antibody-based. Using specific primers, the PCR detects the presence of DNA generated by reverse transcription of the HIV RNA.

13. What are some strategies of the anti-retroviral drugs used in the AIDS treatment?

Anti-retroviral drugs used in AIDS treatment try to approach any of the several steps of the HIV life cycle. There are three main groups of drugs: thereverse transcriptase inhibitors, that attempt to disallow the formation of DNA from the viral RNA (zidovudine, or AZT, ddI, d4T, 3TC, nevirapine, efavirenz, etc.); the protease inhibitors, that block the enzyme protease necessary for the assemblage of new virus (saquinavir, ritonavir, nelfinavir, indinavir); and the group of entry inhibitors (includes fusion inhibitors), that try to block the entry of HIV into the host cell (enfuvirtide, a fusion inhibitor).

14. Why is the AIDS treatment often done with a drug cocktail?

The treatment of acquired immune deficiency syndrome is often done with one or more anti-retroviral drugs of different groups, for example, a protease inhibitor plus a reverse transcriptase inhibitor in an attempt to approach in one single time two or more stages of the HIV life cycle. Besides that, the high mutation rate of the virus may make the treatment ineffective and for this reason the use of the drug cocktail allows physicians to choose other different drug combinations to escape the viral resistance.

15. What are some prophylactic measures against HIV infection?

The main prophylactic measures against HIV infection are: the use of condoms in sexual relations, not to share syringes and needles, careful handling of contaminated medical and nosocomial material, up-to-date information about the virus and its mode of transmission.

Study Tapeworm and Other Worm Diseases

1. What are worm infections?

Worm infections are human diseases caused by platyhelminthes (flatworms) or nematodes (roundworms).

2. What are the most important worm infections?

The most important human worm infections are schistosomiasis, taeniasis, cysticercosis, ascariasis and ancylostomiasis (hookworm infection).

Other important worm infections caused by platyhelminthes are: fascioliasis, caused by Fasciola hepatica, which attacks the liver and the bile ducts; hydatid disease, also known as echinococcosis, caused by a taenia-like parasite and transmitted by feces of dogs in contact with sheep, with a clinical picture similar to cysticercosis. Other important infections caused by roundworms are: strongyloidiasis, agent Strongyloides stercoralis, a common opportunistic disease in AIDS; filariasis, also known as elephantiasis, transmitted by mosquitoes of the Culex genus, caused by Wuchereria bancrofti and other thread-like worms and manifested by obstruction and fibrosis of lymphatic vessels that cause swelling (lymphedema) of limbs; enterobiasis (pinworm infection), caused by Enterobius vermicularis, a worm that parasites the colon and the human perianal region; cutaneous larva migrans, an ancylostomiasis of the skin caused by Ancylostoma braziliensis.

3. What is schistosomiasis?

Schistosomiasis is a worm infection caused by schistosomes, a species of flatworms (platyhelminthes). The disease is prevalent in Latin America and in the Far East. The main species of schistosome found in Latin America is Schistosoma mansoni.

4. How do schistosomes differentiate regarding sex separation?

Schistosomes are dioecious, i.e., the species has separated sexes, male and female individuals.

5. What is the intermediate host of Schistosoma mansoni? Where does that host live?

The intermediate host of the schistosome is a gastropod mollusc, a snail of the Planorbidae family and Biomphalaria genus. The snail vector of schistosomiasis lives in freshwater, as in lagoons and creeks.

6. What is the life cycle of the schistosome?

Male and female adult schistosomes live within blood vessels of the human intestines. The females release eggs that trespass the vessel walls and enter the intestinal lumen being eliminated with the human feces. When in water the egg releases a larva called miracidium that then swims to reach the snail that is the intermediate host. Within the snail miracidia transform into cercariae, another kind of schistosome larva. The cercariae leave the snail and swim until penetrating through the human skin. In humans the cercaria gains the circulation infecting mainly the blood vessels of the intestines, liver or lungs and develops into the adult form of the parasite.

Image Diversity: schistosome life cycle

7. What are the main phases and clinical manifestations of schistosomiasis?

Schistosomiasis has acute and chronic phases. Days after the infection the cercarial dermatitis appears at the site where the worm penetrated the skin. In one or two months the acute phase begins and fever, cough, muscle pain and nausea occur but soon disappear; in some people this phase may not manifest. In the chronic phase of the disease the worm infestation can affect the bowels, causing diarrhea, bloody feces, tiredness and hepatosplenomegaly (enlargement of the liver and spleen). The excessive pressure upon the hepatic portal vein produces varix (collateral circulation) in the esophagus and the patient may have hemorrhages and bloody vomiting that may even cause death.

8. What are the main prophylactic measures against schistosomiasis?

The main measures to prevent schistosomiasis are: information for infected individuals to look for treatment and to not disseminate the disease; chemical and biological combat against the vector snail; basic sanitary conditions to avoid contamination of lakes, rivers and other water streams by infected feces; to avoid contact with fresh water suspected of contamination.

9. What are taenias? What are the diseases caused by them?

Taenias, also know as tapeworms, are platyhelminth animals (flatworms). The main diseases caused by taenias are taeniasis and cysticercosis.

10. How do taenias classify according to the division of sexes?

Taenias are monoecious (hermaphrodite), the same individual has female and male reproductive organs and undergoes self fecundation.

11. What are the two main species of taenias that cause human diseases?

The two mains species of taenias that cause disease in humans are Taenia solium, or the pork tapeworm, and Taenia saginata, or the beef tapeworm.

Besides these species there are still the fish tapeworm, or Diphyllobothrium latum, and a tapeworm, Echinococcus granulosus, which lives in dogs and cause in humans the severe disease known as hydatid disease, or echinococcosis.

Image Diversity: Taenia solium Taenia saginata

12. How do taenias obtain food and make gas exchange?

Tapeworms have hooks and sucking structures on their heads (scolex) that fixate the parasite in the gut wall; these structures often do not injure the host tissue. The parasite obtains food and makes gas exchange through absorption and diffusion across its skin; since it is a platyhelminth it does not have a digestive system or a circulatory system.

13. What are the segments that form the body of the tapeworm called? What is their function?

The body of the tapeworm is made of segments called proglottids. The proglottids are reproductive structures of the taenia and contain the organs that produce male and female gametes. As the proglottids become distant from the scolex (head) they mature. Mature proglottids can fecundate themselves or neighboring ones and the eggs formed are stored inside them. Proglottids called pregnant proglottids, full of eggs, detach from the body of the worm and are eliminated with the human feces.

14. Concerning their respective intermediate hosts how different are Taenia solium and Taenia saginata?

The intermediate hosts of Taenia solium are pigs and the intermediate hosts of Taenia saginata are cattle.

15. What is the life cycle of a tapeworm?

Pregnant proglottids with taenia eggs are released together with human feces. If ingested by the intermediate hosts, swine or bovine, the eggs break inside their intestines and the larva trespass the mucosa and gains the circulation to settle on muscles, heart, brain and other organs of these animals and then differentiate into cystic larvae called cysticerci. Humans become infected when eating raw or badly cooked swine or bovine meat contaminated by cysticerci. In the human intestines the cysticerci develop into adult worms and the cycle goes on.

Image Diversity: taenia life cycle

16. What is the difference between taeniasis and cysticercosis?

Taeniasis is the parasitic disease caused by the adult tapeworm installed within the human intestine.

Cysticercosis occurs when humans ingest eggs or pregnant proglottids of taenias, for example, through badly washed food or self infection. In cysticercosis humans assume the role of intermediate hosts of the parasite and the cysticerci develop within human organs like muscles, brain, eyes and subcutaneous tissue. The brain infestation by cysticerci, a condition known as neurocysticercosis, is extremely severe and may lead to death.

In the normal life cycle of taenias the humans are the definitive hosts and develop taeniasis, a less serious disease, and not cysticercosis.

Image Diversity: cysticercosis

17. If a person eats raw or badly cooked meat infected by Taenia solium or Taenia saginata will this person develop taeniasis or cysticercosis?

If a person eats raw or badly cooked meat infected by Taenia solium or Taenia saginata he or she will develop the disease taeniasis. The ingestion of contaminated raw or badly cooked infected meat means that cysticerci are being ingested. The human then will be affected by taeniases since in his or her gut the cysticerci may develop into an adult tapeworm.

18. How does self infection by tapeworms occur?

Taeniasis patients may develop the most severe form of the worm infection, cysticercosis, because their feces contain eggs and pregnant proglottids of the taenia and there is risk of self infection due to bad hygienic habits, like not washing the hands after defecation. If these individuals ingest the eggs of the parasite they can develop cysticercosis too.

19. What are some prophylactic measures for tapeworm infections?

The main prophylactic measures against taeniasis and cysticercosis are: not to ingest raw or badly cooked swine or bovine meat; sanitary education of the people; appropriate destination of feces; adequate treatment of infected people.

20. What is ascaris? What is the disease caused by this worm?

Ascaris, or Ascaris lumbricoides, is an animal of the nematode phylum, i.e., a roundworm. Ascaris causes ascariasis, a common worm infection of the intestine.

21. How do ascaris obtain food?

The ascaris live within the human gut and feed from the food ingested by the infected person.

22. Does Ascaris lumbricoides present an intermediate host?

Ascaris is a monoxenous parasite, its life cycle is dependent only on one host and so it does not have intermediate host.

23. What is the life cycle of ascaris?

Adult ascaris that live within the human intestine can release up to 200 thousand eggs a day. The eggs are eliminated with human feces and mature in the environment under some heat and moisture conditions. Humans may ingest mature eggs through food contaminated by human feces or through bad hygienic habits. The eggs again inside the human intestine release larvae that cross the enteric mucosa and gain the circulation reaching the lungs. In the lungs the larva mature and go to the airway and to the pharynx when they are then swallowed. Within the gut the larvae develop into adult worms.

Image Diversity: ascaris life cycle

24. What are the main symptoms of the pulmonary and of the intestinal phases of the ascaris infestation?

In the pulmonary phase the ascaris infestation causes cough, hemoptysis, dyspnea, fever, fatigue and may cause a special kind of pneumonia called eosinophilic pneumonia. In the intestinal phase the symptoms are due to spoliation of nutrients of the host and thus hunger and weight loss may appear. Masses of ascaris inside the bowels can cause severe intestinal obstruction.

25. What are some prophylactic measures against ascariasis?

The main prophylactic measures against ascariasis are: efficient washing of vegetables and other foods; basic sanitary conditions and appropriate destination of feces; hygiene education for people; combat against insects that can carry the eggs of the parasite, like flies and cockroaches.

26. What is ancylostomiasis?

Ancylostomiasis is a disease caused by Ancylostoma duodenale or Necator americanus, both hookworms belonging to the nematode phylum (roundworms). Ancylostomiasis caused by these worms is also called hookworm disease.

Since the parasites nourish themselves on human blood the infection causes anemia, hypoproteinemia and the patient often seems pale.

27. Which is the typical feature of the hookworms related to the way they obtain food and explore the host?

Both Ancylostoma duodenale and Necator americanus have mouthparts with hooks or “teeth” that help the fixation of the parasite in the human intestine wall and facilitate the tissue injury necessary to drain blood from the host. The structures are evolutionary adaptations for the parasitic way of life of these animals.

28. Are hookworms monoxenous or heteroxenous?

Hookworms are monoxenous, i.e., their life cycle depends only on one host.

29. What is the life cycle of the hookworms?

Adult hookworms within the human intestine release eggs that are eliminated with the human feces. Under adequate conditions of moisture and temperature the eggs mature in the soil and generate larvae. The larvae differentiate into thread-like infective larvae that can penetrate the human skin, generally through the feet. The larvae them gain the human circulation and reach the lungs from where they go to the airway and the pharynx. When the larvae are swallowed they enter the small intestine and develop into adult worms and the cycle restarts.

Image Diversity: hookworm life cycle

30. What are the main prophylactic measures against hookworm disease?

The main prophylactic measures against hookworm disease are: to avoid walking barefoot on soils suspected of contamination; basic sanitary conditions and appropriate destination of feces; treatment of infected people.

What is a Prion? Learn Below

1. What is a prion?

A prion is an infectious (transmissible) protein able to replicate by transforming other proteins into a copy of the prion. The mechanism of copying is not yet understood by science.

The hypothesis come out from research about a nervous system disease known as Creutzfeldt-Jacob disease, epidemiologically associated to a bovine disease called bovine spongiform encephalitis (the mad cow disease). Research discovered that the infectious agent that causes those diseases, suprisingly, was a protein capable of copying itself and of being transmitted by ingestion (the reason why meat from contaminated animals cannot be consumed), inoculation and even heredity.

Image Diversity: prion

2. What are the main human diseases caused by prions?

The main known human diseases of such type are the Creutzfeldt-Jacob disease (CJD), the kuru and the Gerstmann-Sträussle-Scheinken disease (GSS). The hypothesis that many other diseases of unknown etiological agents are actually caused by self-replicating infectious proteins is strong.

Image Diversity: mad cow disease

Learn Hypertension, Heart Diseases, CVA, Cancer, Alzheimer's and Parkinson's

1. What are degenerative diseases?

Degenerative diseases are non infectious prevalent diseases whose incidences increase with aging.

2. What are risk factors for diseases?

Risk factors for a disease are everything that contributes to increase the risk of the disease to appear. For example, for most cardiovascular diseases, tobacco smoking and diabetes mellitus are both important risk factors; for some cancers having a genetic component a positive family history is a risk factor, etc.

3. What are the main human degenerative diseases?

The main human degenerative diseases are divided into three groups: cardiovascular diseases, neoplastic diseases and degenerative diseases of the nervous system. The main cardiovascular diseases are hypertension, the cardiopathies, including coronary disease and myocardial infarction, and the cerebrovascular accidents (CVAs, or strokes). Neoplasias are benign tumors and cancers. The main degenerative diseases of the nervous system are Alzheimer's disease and Parkinson's disease.

4. What is hypertension?

Hypertension is a disease in which the arterial blood pressure, during systole or during diastole, is abnormally high.

Hypertension, or high blood pressure, is a condition that must be diagnosed and treated since it produces irreversible injuries in arteries and, later, it causes other severe diseases in organs like the heart, brain, kidneys, retina, etc.

Image Diversity: blood pressure

5. What are the main risk factors for hypertension?

The main risks factors for hypertension are tobacco smoking, stress, obesity, sedentary lifestyle and alcoholism.

6. What is the relation between the maximum and the minimum blood pressure with the phenomena of systole and diastole?

The maximum blood pressure is the pressure on the wall of the systemic arteries during systole, i.e., when the heart is pumping blood to arterial vessels. The minimum blood pressure is the pressure on the wall of the systemic arteries during diastole, i.e., when the heart ventricles are relaxing and getting blood.

7. What are the main degenerative diseases of the heart?

The main degenerative diseases of the heart are heart failure, arrhythmias, valvular heart diseases, coronary insufficiency and myocardial infarction.

Image Diversity: heart failure arrhythmias valvular heart disease

8. What is coronary disease?

Coronary disease, or coronary insufficiency, is a disease in which there is total or partial obstruction of one or more of the arteries that irrigate the heart musculature, i.e., obstruction of the coronary arteries. The disease is formed by slow and gradual formation of atheroma plaques inside the coronaries. The fatty plaques grow and block the flow of blood, a process known as atherosclerosis (do not confuse with arteriosclerosis which is the hardening of the arteries generally cause by chronic high blood pressure).

The main risk factors for coronary disease are tobacco smoking, diabetes mellitus, hypertension, hypercholesterolemia (high level of bad cholesterol and low level of good cholesterol), stress, alcoholism and sedentary lifestyle.

Coronary disease may present in two manners, as angina pectoris or as myocardial infarction. If the arterial obstruction is not complete and extensive the patient often feels chest pain (angina pectoris), mainly when performing physical exercise or in any situation when the heart needs more oxygen. If the obstruction of one or more coronaries is complete or blood cannot irrigate some regions of the heart muscle (myocardium) the infarction occurs and the muscle cells of the affected area die.

Image Diversity: coronary disease coronary circulation atheroma plaque

9. What is myocardial infarction?

Myocardial infarction is the condition in which an area of this tissue or the entire heart muscle dies by hypoxia due to lack of blood irrigation. Myocardial infarction is a severe disease since on the dependence of its extension the heart can fail, i.e., it can no longer pump blood to the lungs or to the body or it can even stop beating (causing death).

The main cause of myocardial infarction is coronary obstruction, blocking of the arteries that carry arterial blood to the heart muscle. Other events like hemodynamic shock (circulation stoppage due to large hemorrhages, for example) can also causemyocardial infarction.

Image Diversity: myocardial infarction

10. What is coronary bypass graft?

Coronary artery bypass graft is a kind of surgical myocardial revascularization, i.e., a way to provide blood to a myocardium whose blood supply is impaired or blocked due tocoronary disease. In this surgical treatment of coronary disease one or more blood vessel grafts taken from other parts of the body are used to join the obstructed artery (in a region after the obstruction) with the aorta or other healthy coronary artery thus reestablishing the blood flow to the myocardium. Often the blood vessel grafts are part of the saphenous vein from the leg or of the mammary artery from the chest or even of the radial artery from the forearm.

Image Diversity: coronary bypass graft

11. What are cerebrovascular accidents?

Cerebrovascular accident (CVA), also known as stroke, is the generic name given to infarction (tissue and cellular death by hypoxia) of areas of the brain due to vascular obstruction or hemorrhages. CVAs are divided into ischemic and hemorrhagic. In the ischemic CVA blocking of arteries that carry blood to the brain occurs; its cause is generally atherosclerosis (atheroma formation) of these vessels. In the hemorrhagic CVA there is rupture of one or more blood vessels of the brain with blood leakage, increasing intracranial pressure and thus interruption of blood flow in some areas of the brain. The severity of the stroke depends on the function performed by the affected area of the brain, for example, motor function, visual function, vegetative function, etc., and on the size of the involved area.

The main risk factors for cerebrovascular accidents are hypertension, hypercholesterolemia, tobacco smoking and old age.

Image Diversity: cerebrovascular accidents

12. What are neoplasias?

Neoplasia is any abnormal and uncontrolled proliferation of cells of an organism. Neoplasias can be benign or malign. Benign neoplasias are those in which the cell proliferation is limited to a given site of the body and so neoplastic cells do not spread to other close regions or at distance through the circulation. Malign neoplasias are those in which the neoplastic cells disseminate at distance to other sites and organs of the body, a process called metastasis, where they continue to proliferate. Malign neoplasias injure tissues and if not eradicated they are fatal. Benign neoplasia can also be deadly when it forms a tumor that grows and compresses vital organs.

Image Diversity: neoplastic cells

13. How different are the concepts of neoplasia, tumor and cancer?

Not every tumor is neoplastic and not every neoplasia creates tumor. Tumor is the generic name given to the abnormal increase in mass or volume of any area of the body (for example, the enlarged tonsils during throat infection are a kind of tumor, any inflammation creating a swelled area characterize a tumor, etc.). Neoplasias can form tumors, some of them very large, by aggregation of neoplastic cells in the region where the neoplasia began or in distant implantations. Cancer is a synonym for malign neoplasia.

14. What is cancer?

Cancers are malign neoplasias, i.e., abnormal and uncontrolled proliferation of cells that can disseminate to other sites of the body. Cancer dissemination at distance usually occurs through blood or lymphatic vessels.

15. How do malign neoplasias appear?

Neoplasias appear due to DNA mutations in genes that regulate the cellular proliferation thus making the cell lose its capacity to control and limit its division by mitosis. The cell then divides continuously and uncontrollably and this defect is transmitted to its daughter cells.

16. What are carcinogens?

Carcinogens are factors capable of producing neoplasias. Any mutagen, a substance that can induce DNA mutation, is a potential carcinogen. Examples of carcinogens are radiation, nitrous acid, many substances inhaled through tobacco smoking and the human papilloma virus (HPV).

17. How do cells of neoplastic tumors obtain oxygen and nutrients and release wastes?

In neoplastic tumors a phenomenon called angiogenesis occurs. Angiogenesis is the formation of new blood vessels. Neoplastic cells induce the formation of new blood vessels to irrigate and drain the neoplastic tissue.

Angiogenesis is important because the tumor growth depends on it. A lot of research on cancer has tried to discover natural and synthetic substances to inhibit angiogenesis.

Image Diversity: angiogenesis

18. What are the main types of cancer that affect humans?

Excluding skin cancer, that are the more easily detected and so cases are registered in larger number, the main types of cancer in men are prostate cancer, lung cancer, stomach cancer; in women, breast cancer, colon and rectal cancer and lung cancer are of great incidence. Other common cancers are ovarian cancer, pancreatic cancer, liver cancer, esophageal cancer, brain cancer and the leukemias and lymphomas (blood cancers).

Epithelial cancers, of the skin as well as of the internal organs, are more common because epithelial tissues are more exposed to carcinogens.

The proportional incidence of the many types of cancers varies according to the considered population.

19. What is the main risk factor for lung cancer?

The main risk factor for lung cancer is tobacco smoking. The large number of cases of this type of cancer is due to the increased number of smokers worldwide.

Image Diversity: lung cancer

20. What is the main risk factor for skin cancer?

The main risk factor for skin cancer is solar exposition of the skin without protection against ultraviolet radiation (a potential carcinogen).

The most lethal skin cancer is melanoma.

Image Diversity: skin cancer

21. How is cancer usually treated?

If the cancer is in its initial stage treatment is often done by surgical removal of the neoplastic tissue. Cancers already disseminated are often treated with radiation (radiotherapy) and anti-mitotic drugs (chemotherapy).

22. What are the main degenerative diseases of the nervous system?

The main degenerative diseases of the nervous system are Alzheimer’s disease and Parkinson’s disease.

Degenerative diseases of the nervous system are caused by progressive tissue degradation or loss of neurons in some regions of the nervous system.

23. What is Alzheimer’s disease?

Alzheimer’s disease is a degenerative disease of the central nervous system in which the patient has progressive dementia and alteration of mental functions.

The disease generally appears after 40 years of age and it is more frequent in the elderly. Image studies of the brain show broad loss of brain tissue. (The Alzheimer’s disease should not be confused with other mental deteriorations common in the elderly.)

Image Diversity: Alzheimer's disease

24. What is Parkinson’s disease?

Parkinson’s disease is a degenerative disease of the nervous system in which the main manifestations are progressive motor disturbances, like tremors of feet, hands and mandibles (jaws) and walking and balance impairments. Parkinson’s disease is due to the degeneration of dopaminergic motor neurons, i.e., motor neurons that use dopamine as a neurotransmitter, located in a specific region of the brain, the mesencephalon. Such degeneration creates deficiency of dopamine in the nervous system. (Parkinson’s disease should not be confused with other causes of tremors, like the use of some medicines.)

Image Diversity: Parkinson's disease