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
ingestion of oocysts sporozoites penetrate intestinal epithelium rapid intracellular replication (any cell) dissemination via macrophages
Tachyzoite Stage
merogony 'merozoites' typical apicomplexan
motile invasive stages intracellular replication
Endodyogony
'binary fission' = endodyogony
Tachyzoite Stage
repeated rounds of merogony acute stage infection primarily in reticuloendothelial cells
Bradyzoite Stage
dormant, slowly replicating due to host immune response chronic or latent infection tissue cysts primarily in brain and muscle
Bradyzoite Stage
dormant, slowly replicating due to host immune response chronic or latent infection tissue cysts primarily 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)
Recent Expansion of Toxoplasma
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 or shortly before pregnancy
can only occur once 1/3 will pass infection to fetus
typical disease manifestations include: retinochoroiditis, psychomotor disturbances, intracerebral calcification, hydrocephaly, microcephaly
incidence ~1 per 1000 births severity varies with age of fetus
move severe early in pregnancy more frequent later in pregnancy
Prevalences of Outcomes
5-10% death 8-10% severe brain and eye damage 10-13% moderate-severe visual impairment 58-72% asymptomatic at birth, many developing retino-choroiditis or mental impairment
infection can result in: spontaneous abortion, still birth, premature birth, or full-term overt disease
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
various serological tests active (acute) vs chronic infection
compare samples at 2 week intervals IgM > IgG; Ab titers
Treatment
recommended: anti-folates (pyrimethamine + sulfadiazine) clindamycin for children spiramycin for prophylatic use during pregnancy Condition Duration Comments
symptomatic disease active retinochoroiditis asymptomatic children (<5) immunocompromised until symptoms subside and evidence of immunity until symptoms subside + corticosteriod (antiand evidence of immunity inflammatory) prevents 3-6 weeks retinochoroiditis 4-6 weeks after symptoms subside + continued + folinic acid in AIDS prophylaxis
seldom by direct parasite demonstration
biopsy inoculation into mice or cell culture (only acute stage)
Prevention
Raw Meat
cook meat thoroughly
An Enigma
Several studies show no correlation between cat contact and Toxoplasma. But dog contact is highly correlated with Toxoplasma transmission. Frenkel et al (1995) AJTMH 53:458
Cat Feces
clean litter box
(66 C, 150 F)
wear gloves when
handling
wash hands after
promptly (<24 hr) wear gloves keep cat in house cover sand box no cats in home control strays
