Specific Antibody Indicates Route of Parasitic Infection

A protein that elicits an antibody to the parasite Toxoplasma gondii may help scientists determine the mode of transmission.

The T. gondii embryogenesis-related protein (TgERP) can be detected in the sera of humans and animals by difference gel electrophoresis, in combination with tandem mass spectroscopy and Western blot analysis.

A team of scientists, led by those at the Animal and Natural Resources Institute (Beltsville, MD, USA), selected a recombinant protein from a complementary DNA (cDNA) library constructed from T. gondii sporozoites and it was used for Western blots and probed with sera from T. gondii-infected humans. The investigators 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.

Serum antibody to the antigen TgERP was detected in humans within 6-8 months of initial oocyst-acquired infection. Of 163 individuals in the acute stage of infection, where anti–T. gondii immunoglobulin M (IgM) was detected in sera, or where the IgG avidity test was less than 30%, 103 (63.2%) had detectable antibodies that reacted with TgERP. Of 176 individuals with unknown infection route and in the chronic stage of infection, where no anti–T. gondii IgM was detected in sera, or with greater than 30% result in the IgG avidity test, antibody to TgERP was detected in 31(17.6%) samples.

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. Congenital infection can bring about a range of outcomes for the child, including chronic infection, blindness, mental retardation, and stillbirth. Until now, no tests were able to differentiate between oocyst ingestion and tissue cyst ingestion as the infection source.

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. 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." The study was published in April 2011, in the Journal of Parasitology.

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