Toxoplasma Gondii
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Contents |
Introduction
- A obligate intracellular parasite with worldwide distribution in hosts: human; domestic & wild birds & mammals, especially carnivores. The sexual stage in the life cycle occurs within intestinal epithelium of felines ( cats) which are exclusive & definitive hosts. Asexual & sexual reproduction ( schizogony & gametogony) lead to development of immature oocysts which are passed in the feces. Maturation into infective oocysts containing 2 sporocysts each with 4 sporozoites occurs over 2-21 days. Ingestion of infective oocysts in susceptible hosts leads to disruption of cysts with release of sporozoites which then transform into tachyzoites ( trophozoites). Tachyzoites may infect any nucleated cell. Proliferation of tachyzoites leads to cell death & host injury during the acute phase of infection. After immunity develops, cysts are formed in tissues which may contain thousands of slowly growing bradyzoites. Tissue cysts are characteristic of chronic infection. All stages of the life cycle occur in felines, but only trophozoites occur in humans & other intermediate hosts. Tachyzoites are crescent or oval shaped 3 x 7 um. Cysts are generally spherical measuring up to 30 um in diameter. In muscle, cysts may appear elongated.
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References
- Clinical Diagnosis & Management by Laboratory Methods, 19th edition, J.B. Henry (ed), W.B. Saunders Co., Philadelphia, PA. 1996, pg 1268-69
- Harrison's Principles of Internal Medicine, 14th ed. Fauci et al (eds), McGraw-Hill Inc. NY, 1998, pg 1197-1201
