Parasite Alleles Linked to Severe Illness in Newborns

Strains of the Toxoplasma gondii parasite have been identified that are most strongly associated with premature births and severe birth defects.

A new blood test has been developed detect the presence of strain-specific antibodies to pinpoint T. gondii strains that children acquire from their acutely infected mothers while in the womb.

Scientists at the US National Institute of Allergy and Infectious Diseases (NIAID; Bethesda, MD, USA) applied the test to blood samples collected between 1981 and 2009 as part of the National Collaborative Chicago-Based Congenital Toxoplasmosis Study. Sera were obtained from 183 mothers who transmitted T. gondii to their fetuses and 151 infants, most diagnosed with substantial disease as newborns.

Studies performed included the Sabin-Feldman Dye test; immunoglobulin G (IgG) and immunoglobulin M (IgM) enzyme linked immunosorbent assays (ELISA) on maternal serum; IgM immunosorbent agglutination assay on newborn samples; immunoglobulin A (IgA) ELISA on mother and child sera; differential agglutination tests and avidity assays on maternal samples. Presence of strain-specific antibodies in people infected by parasites with type II or non-II alleles was determined in an ELISA using polymorphic peptides derived from two T. gondii dense granule proteins (GRA6 and GRA7) and two control peptides coupled to keyhole limpet hemocyanin (Biosource; Camarillo, CA, USA).

The scientists found evidence of either type II or not exclusively type II strains (NE-II) infections in 183 of the mother-child pairs in the national congenital toxoplasmosis study. The NE-II parasites were more likely to be associated with premature birth, and infants infected with these strains were more likely to have severe manifestations of disease than infants infected by type II parasites. Severe eye damage was seen in 59 out of 88 (67%) of NE-II cases, while such eye damage was present in only 18 out of 46 (39%) of type II cases.

Rima McLeod, MD, from the University of Chicago (IL, USA) and principal author of the study, said, "In the United States, obstetrical screening for Toxoplasma infection is rarely practiced. This new study underscores the value of identifying all patients who will benefit from treatment and suggests that widespread screening and treatment of pregnant women who are infected could prevent infants from suffering eye and brain damage due to congenital toxoplasmosis." The study was published on April 11, 2012, in the journal Clinical Infectious Diseases.

Related Links:
US National Institute of Allergy and Infectious Diseases
Biosource
University of Chicago