Author
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Fayer, Ronald |
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Submitted to: American Society of Tropical Medicine and Hygiene
Publication Type: Abstract Only Publication Acceptance Date: 11/1/2002 Publication Date: 12/1/2002 Citation: FAYER, R. ANIMAL RESERVOIRS, VECTORS, AND TRANSMISSION OF PATHOGENIC PROTOZOA. AMERICAN SOCIETY OF TROPICAL MEDICINE AND HYGIENE. 2002. Interpretive Summary: Technical Abstract: Cryptosporidium Cryptosporidiosis in humans and ruminants presents primarily as a diarrheal disease. Although some highly virulent isolates have caused mortality in cattle, other less virulent isolates can cause morbidity and mortality in immunosuppressed humans and animals. Of 12 named species of Cryptosporidium only Cryptosporidium parvum is widespread in humans and an estimated 150 or more other species mammals but 4 other species have now been identified in human infections. Cryptosporidia develop intracellularly in the gastrointestinal tract and form oocysts that are excreted in the feces. Fecal-oral transmission of the oocyst stage results in infection from ingesting contaminated drinking water, food, and recreational water. Species and isolates are nearly identical and therefore difficult or impossible to identify by microscopy. Molecular methods identify genotypes of Cryptosporidium by RAPD, RFLP, and sequence analysis. Because most reports of cryptosporidiosis have not been characterized by methods other than microscopy, infections may actually result from several species. Most Cryptosporidium isolated from immunocompromised persons have been the human and cattle genotypes, but a few persons have been found infected with genotypes originally associated with cat, dog, and turkey hosts. Two healthy persons have passed oocysts resembling C. muris, originally a parasite of rodents. These findings indicate that a variety of animals might be sources of Cryptosporidium for humans. Filth flies, birds, and shellfish have been identified as mechanical vectors of oocysts. These findings indicate the need for molecular characterization of specimens so the epidemiology can be better understood (Fayer et al., 2001) Toxoplasma Toxoplasma gondii is an obligate intracellular parasite with a coccidian life cycle. It develops in the intestine of members of the cat family, forming oocysts that are excreted in the feces. To become infectious, oocysts require several days exposure to moisture and air. In vertebrates other than felids they parasites develop in extra-intestinal sites causing tissue damage, inflammation, and disease. In immunocompetent hosts that survive the acute infection, cysts develop around slowly multiplying bradyzoites. Oocysts can be transmitted by ingestion of contaminated food or water, or by direct exposure to cat feces. Tachyzoites can be transmitted via the placenta to a fetus, or by blood transfusion causing asymptomatic infection, clinical illness, or death. When meat or organs containing cysts are eaten by carnivores, including humans, they initiate parenteral infection. When persons that harbor cysts become immune compromised, tachyzoites develop, often in the central nervous system, causing lesions, illness, and possibly mortality. Transplantation of organs harboring cysts can result in the same sequence of events. All stages (oocysts containing sporozoites, tachyzoites, and bradyzoites) are infectious for felids. Flies and worms have been shown to mechanically transport oocysts. Over 350 vertebrates are reported to have been infected with T. gondii. Domesticated and wild felids are the only final hosts; i.e., only felids excrete oocysts. The prevalence of T. gondii in felids, based on seroepidemiological studies, is high. Antibodies to T. gondii in trapped lynx and bobcats from Quebec, Canada using the modified agglutination test (Labelle et al., 2001) was 44 and 40%, respectively. These findings suggest that T. gondii is widespread in the wild and that exposure to wild felids and game animals may represent a potential source of infection for humans. Seroprevalence data for T. gondii in 865 captive neotropical felids in Brazil, indicated antibodies to T. gondii in 54.6% of cats, 45.9% of jaguarundis 57.7% of ocelots, 51.9% of oncillas, 55.5% of margays, 12.5% of Pampas-cats, 75% of Geoffroys-cats, 63 |
