Toxoplasma gondii cosmopolitan distribution seropositive prevalence rates vary generally 20-75% generally causes very benign disease in immunocompetent adults tissue cyst forming coccidia predator-prey life cycle felines are definitive host infects wide range of birds and mammals (intermediate hosts) Definitive Host adult forms sexual reproduction Intermediate Host immature forms asexual reproduction

Typical Isospora Life Cycle in Felines

Typical Isospora Life Cycle in Felines fertilization within infected host cells immature oocysts in feces sporulation in environment (1-4 d)

Tachyzoite Stage sporozoites  merogony rapid replication dissemination via macrophages reticuloendothelial cells acute stage infection

Endodyogony

Tachyzoite Stage sporozoites  merogony rapid replication dissemination via macrophages reticuloendothelial cells acute stage infection

Tachyzoite Stage sporozoites  merogony rapid replication dissemination via macrophages reticuloendothelial cells acute stage infection

Bradyzoite Stage dormant, slowly replicating due to host immune response chronic or latent infection tissue cysts in brain and muscle

Bradyzoite Stage dormant, slowly replicating due to host immune response chronic or latent infection tissue cysts in brain and muscle

“Fatal Attraction in Rats Infected with Toxoplasma gondii” non-infected rats (n=32) infected rats (n=23) visits to scented areas own neutral rabbit cat From Berdoy et al (2000) Proc. R. Soc. (Biol.) 267:1591

Human Transmission ingestion of sporulated oocysts (cat feces + incubation) ingestion of zoites (undercooked meat) congenital infection (only during acute stage) organ transplants chronic infection in donor immunosuppression blood transfusions (only during acute stage)

Acquired Postnatal Toxoplasmosis 1-2 week incubation period acute parasitemia persists for several weeks until development of tissue cysts often asymptomatic (>80%) a common symptom is lymphadenopathy without fever occasionally mononucleosis-like (fever, headache, fatigue, myalgia) likely persists for life of patient immunosuppression can lead to reactivation (eg., organ transplants)

Toxoplasmic Encephalitis common complication associated with AIDS during the 1980's recrudescence of latent infection multifocal disease associated with immunosuppression lesions detectable with CT or MRI little spread to other organs symptoms include: lethargy, apathy, incoordination, dementia progressive disease  convulsions

Congenital Toxoplasmosis 1o infection must occur during pregnancy can only occur once 1/3 will pass infection to fetus incidence ~1 per 1000 births severity varies with age of fetus move severe early in pregnancy more frequent later in pregnancy infection can result in: spontaneous abortion, still birth, premature birth, or full-term ± overt disease

typical disease manifestations include: retinochoroiditis, psychomotor disturbances, intracerebral calcification, hydrocephaly, microcephaly

Ocular Toxoplasmosis retinochoroiditis: likely due to both active parasite proliferation and immune hypersensitivity generally a recrudescence--rarely from primary infection congenital infection 20% exhibit ocular symptoms at birth 82% by adolescence most lesions are focal and self-limiting rapidly destructive in AIDS patients

Ocular Toxoplasmosis retinochoroiditis: likely due to both active parasite proliferation and immune hypersensitivity generally a recrudescence--rarely from primary infection congenital infection 20% exhibit ocular symptoms at birth 82% by adolescence most lesions are focal and self-limiting rapidly destructive in AIDS patients

Diagnosis seldom by direct parasite demonstration biopsy inoculation into mice or cell culture (only acute stage) various serological tests active (acute) vs chronic infection compare samples at 2 week intervals IgM > IgG;  Ab titers

Prevention

Frenkel et al (1995) AJTMH 53:458 But dog contact is highly correlated with Toxoplasma transmission. Several studies show no correlation between cat contact and Toxoplasma. An Enigma