Toxoplasma gondii
is a one-celled parasite (Phylum Protozoa) that causes toxoplasmosis in humans. Toxoplasma is usually acquired from cat feces or raw meat. Cats who harbor Toxoplasma may be asymptomatic but shed the organism in their feces. If Toxoplasma are ingested by humans, they reproduce in the brain, eye or skeletal muscle. Contact with the dried feces of cats, such as when cleaning a litter box, may lead to infection. In addition, a human who eats raw or undercooked meat of an infected animal (any mammal or bird) may become infected with the parasite. Particular concern arises when pregnant women acquire Toxoplasma because the parasite may cross the placenta, infecting the infant, and leading to congenital defects such as hydrocephaly ("water on the brain"). In recent years Toxoplasma has been identified as a relatively common opportunistic pathogen for AIDS patients.Because Toxoplasma has no means of locomotion, it is a member of the class Sporozoa.
Diagnosis depends on finding the crescent shape of Toxoplasma in biopsied tissue or body fluids, a positive serology test, or mouse inoculation. Toxoplasma is shown in these images at 100 X magnification.
Click on each image to see the enlarged version.
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