Infection with the obligate intracellular parasite Toxoplasma gondii causes toxoplasmosis. Most healthy individuals will likely only experience some mild flu-like symptoms. However, immunosuppressed people such as those with HIV/AIDS, those undergoing chemotherapy or those who received an organ transplant are susceptible to acute toxoplasmosis or to reactivation of latent Toxoplasma. When a pregnant woman is infected for the first time Toxoplasma can transverse the placenta, infect the fetus and cause severe birth defects. Severity of symptoms in children born with toxoplasmosis depend on during what month of pregnancy a woman was infected and likely also the exact genotype of the infecting strain. Toxoplasma can also cause ocular disease and is a leading cause of blindness in South America. There is good evidence that certain Toxoplasma strains are associated with ocular disease in otherwise healthy individuals. My lab is interested in determining the mechanism explaining why Toxoplasma strains differ in pathogenesis.
To determine if a person has acute or chronic toxoplasmosis a test for antibodies against Toxoplasma is performed. High levels of IgM indicate acute infection while absence of IgM but presence of Toxoplasma-specific IgG indicates chronic infection. Because IgM can stay high for quite a long time the avidity of IgG is also often used to determine the time of infection as longer infections are associated with higher affinity IgG. For more info visit the Toxoplasma Serology Laboratory.
The current therapy (pyrimethamine, sulfadiazine and folinic acid) against Toxoplasma can only treat the acute disease and does not remove the latent chronic phase.