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Infection is often asymptomatic. Immunocompetent individuals may present with fever, lymphadenopathy, muscle aches, and headache. Congenitally infected children may suffer impaired vision and mental retardation. Immunosuppressed patients may have central nervous system disease (encephalitis).
Members of the cat family (Felidae) are the definitive hosts; many mammals and birds serve as intermediate hosts. Infection is contracted by ingesting either oocysts or meat containing live organisms. Organisms enter the intestinal epithelium and can spread to many host tissues. Individual organisms are lunate, about 6 × 2 μm, and multiply within host cells. Tissue cysts containing hundreds of quiescent organisms may form as infection wanes. Toxoplasma reproduces sexually only in cats. Organisms infecting the intestinal epithelium produce oocysts which are shed in the feces. Mature oocysts are approximately 12 μm in diameter and contain eight infective sporozoites.
Toxoplasma gondii, a member of the Apicomplexa, is the sole species.
A sexual multiplication by cell division can occur in virtually any host cell.
Host cells are destroyed by active multiplication of T gondii. Necrotic foci may result. Congenital infection often involves the retina and brain; focal chorioretinitis may result in impaired vision. Brain involvement in immunosuppressed patients may lead to large necrotic abscesses. Disease reactivation in immunosuppressed patients may result from the rupture of a tissue cyst.
Immunocompetent individuals mount an effective cell mediated immune response that eradicates active infection within weeks or months and results in immunity against reinfection. Tissue cysts are unreactive and may persist for the life of the host.
Toxoplasmosis shows a nonseasonal worldwide distribution. Most natural infections are acquired by ingesting undercooked meat containing tissue cysts or food contaminated by cat feces.
Diagnosis is based on serology and on histologic examination of tissues.
Infection may be prevented by thorough cooking of meat and by proper management of cats. Acute cases are treated with sulfadiazine and pyrimethamine.
