Malaria, Chagas' Disease and Other Protozoan Infections Easy Q&A Review 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 for the 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 the Trypanosoma 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