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)

•sporozoites merogony• rapid replication•dissemination via macrophages

• reticuloendothelial cells•acute stage infection

Tachyzoite Stage

Endodyogony

•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

Tachyzoite Stage

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”

From Berdoy et al (2000) Proc. R. Soc. (Biol.) 267:1591

non-infected rats (n=32)infected rats (n=23)

visits to scented

areas

own neutral rabbit cat

• 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)

Human Transmission

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

Prevalences of Outcomes5-10% death8-10% severe brain and eye damage

10-13% moderate-severe visualimpairment

58-72% asymptomatic at birth, manydeveloping retino-choroiditisor mental impairment

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

Treatment recommended: anti-folates (pyrimethamine + sulfadiazine) clindamycin for children spiramycin for prophylatic use during pregnancy

Condition Duration Commentssymptomaticdisease

until symptoms subsideand evidence of immunity

active retino-choroiditis

until symptoms subsideand evidence of immunity

+ corticosteriod (anti-inflammatory)

asymptomaticchildren (<5)

3-6 weekspreventsretinochoroiditis

immuno-compromised

4-6 weeks after symptomssubside + continuedprophylaxis

+ folinic acid in AIDS

Raw Meat Cat Feces• cook meat thoroughly

(66oC, 150oF)• wear gloves when

handling• wash hands after

• no cats in home• clean litter box

promptly (<24 hr)• wear gloves• keep cat in house• cover sand box• control strays

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