Toxoplasma Infection (PUBH 4104) PDF

PUBH 4104 Foodborne Disease Protozoan Infections Toxoplasma 1 Toxoplasma o Toxoplasma gondii is an obligate, intracellular coccidian protozoan, the illness is called toxoplasmosis o Common routes of infection are: o Oral ingestion of the parasite...

PUBH 4104 Foodborne Disease Protozoan Infections Toxoplasma 1 Toxoplasma o Toxoplasma gondii is an obligate, intracellular coccidian protozoan, the illness is called toxoplasmosis o Common routes of infection are: o Oral ingestion of the parasite o Through raw or undercooked meat containing tissue cysts o Through water or food contaminated with oocysts o Transplacental (congenital) transmission to the fetus o Transmission through transplanted organs or blood transfusions 2 Toxoplasma o There are three forms of the parasite that concern us: o Oocysts, are products of the sexual cycle, shed only from the definitive host, the common cat. o When oocysts sporulate, they form bradyzoites which are released by enzymes in the host digestive tract. The bradyzoites invade the intestinal cells and form tachyzoites which can travel through the blood and/or lymph. o Tissue cysts are packed full of bradyzoites, formed when tachyzoites are exposed to the host immune response, and change back to the bradyzoite form. (inactive, but can reactivate) 3 Toxoplasma o Oocysts are formed in the small intestine of the cat and are shed in the feces for 10-14 days: o They are resistant to external environmental conditions o 10 million per day may be shed o Must sporulate before becoming infectious, takes 2-21 days depending on temperature and oxygen availability o May remain infectious up to 12 months under favorable conditions 4 Toxoplasma o Humans become infected by ingesting tissue cysts or oocysts. Infectious dose is unknown. o Outer wall of either are degraded by digestive enzymes and the parasite is liberated into the intestinal lumen o The tachyzoites spread to various cells and tissues of the body, commonly those of the brain and striated muscles (skeletal and cardiac) o Bradyzoites form in tissue cysts, as described earlier. 5 6 Toxoplasma o Primary infection in any host often goes unrecognized (asymptomatic) o About 10% - 20% of individuals will see a self-limited and nonspecific illness o Lymph node swelling and soreness o Muscle pains o Fatigue o May last days to months o Tissue cysts will remain viable for the life of the host. 7 Toxoplasma o Toxoplasmosis in pregnant women is usually symptomatic, but tachyozoites can cross the placenta o Damage to the fetus may be: o Miscarriage or stillbirth o Head deformities o Brain or eye damage o Infants may also be infected at birth, not show any symptoms, but see effects later in life. 8 Toxoplasma o In immunocompromised patient's toxoplasmosis is almost always the result of reactivation of previously acquired infection o Often a life-threatening disease in this population o The brain is often targeted (encephalitis) o Confusion, nausea, poor coordination and seizures may occur. 9 Toxoplasma o Prevention and Control o Most susceptible groups are pregnant women and the immunocompromised who are seronegative o Tissue cysts in meats are rendered noninfectious by proper cooking, smoking, curing or freezing to -20°C o Hands should be washed properly after handling raw meat or vegetables o Eggs should not be eaten raw o Unpasteurized milk should be avoided o Cat litter boxes and sandboxes should be treated effectively o If cleaned daily the oocysts have no chance of sporulating 10 11