Toxoplasmosis update and public health implications.

Toxoplasma gondii has a coccidian life cycle in the intestine of domestic and wild felids that includes a series of asexual and sexual stages and an oocyst stage that is shed in the feces. Oocysts complete their development outside the body, eventually becoming infective for about 350 species of vertebrates including cats and man. The effects of climate on oocyst survival and the physical and biological means of oocyst dispersal are discussed. Infectivity and pathogenicity for livestock species vary. Acute disease results from rapidly multiplying tachyzoites that may be transmitted by carnivorism, transfusion, vertical transmission and other routes. Patent infections may persist for the life of a host as bradyzoites within tissue cysts. Bradyzoites initiate acute infection in other hosts after carnivorism or organ transplantation or in the same host after immunosuppression. Also discussed are: (a) prevalence of T. gondii in livestock as determined by digestion and serological techniques, (b) identification in humans as accomplished by isolation, serological and skin test techniques and (c) identification in cats as accomplished primarily by fecal examinations for oocysts infective for mice. Source of human infections, major outbreaks, treatment, effects on mental health and methods for preventing toxoplasmosis in man and livestock are listed.