Figuring out how we contracted an illness can help us determine what steps to take next. In the case of infectious disease, epidemiological studies can offer insight into treatment and prevention.
Toxoplasmosis, a common parasitic infection, has provided scientists with a particular challenge because several routes of infection are possible and current tests are unable to differentiate between them.
A study in the April issue of the Journal of Parasitology reports the first identification of a sporozoite-specific protein, TgERP, that is leading to the isolation of forms of toxoplasmosis infection. This protein elicits an antibody in Toxoplasma gondii, the species of parasitic protozoa that causes toxoplasmosis. The research was conducted by a team of scientists from several institutions, led by Dolores Hill and J.P. Dubey of the United States Department of Agriculture-Agricultural Research Service, Animal and Natural Resources Institute, Animal Parasitic Diseases Laboratory in Beltsville, Maryland.
Toxoplasmosis is a common parasitic infection found in humans and warm-blooded animals worldwide. Nearly one-third of humanity has been exposed to this parasite. While adults rarely are severely affected by toxoplasmosis, it poses a significant threat to pregnant women, who transmit the pathogen to the fetus, and to those with suppressed immune systems, such as organ transplant patients and people with acquired immunodeficiency syndrome (AIDS). Congenital infection can bring about a range of outcomes for the child, including chronic infection, blindness, mental retardation, and stillbirth.
Other than congenital, the routes of infection include ingestion of food or water contaminated with oocysts from infected cat feces and ingestion of tissue cysts in undercooked or raw meat. Food animals, such as pigs, can also become infected, resulting in people consuming meat products containing tissue cysts. No tests are able to differentiate between oocyst ingestion and tissue cyst ingestion as the infection source.
However, this study shows that the presence of the antibody elicited by the TgERP protein can identify people infected through ingestion of oocysts within six to eight months of their initial exposure. Researchers used blood sera from laboratory tests performed with pigs and mice, as well as human blood sera from six events of known occurrences of toxoplasmosis.
In these tests, antibody to TgERP was effectively identified in all pigs exposed to oocyte infection and 90% of people known or suspected to have been exposed to oocysts. Overall, 63% of 163 individuals in the acute stage of infection had detectable antibodies that reacted with TgERP. The authors conclude that "TgERP may be useful in detecting exposure to sporozoites in early Toxoplasma infection and implicates oocysts as the agent of infection."