Scientists have identified which strains of the Toxoplasma gondii parasite, the cause of toxoplasmosis, are most strongly associated with premature births and severe birth defects in the US. The researchers used a new blood test developed by scientists at the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health, to pinpoint T. gondii strains that children acquire from their acutely infected mothers while in the womb.
Pregnant women can become infected with T. gondii through contact with cat feces that contain infectious forms of the parasite or by eating undercooked meat. Women who become infected while pregnant may miscarry, give birth prematurely, or have babies with eye or brain damage.
“If undetected or untreated, congenital toxoplasmosis can have serious consequences for a child’s quality of life,” noted NIAID Director Anthony S. Fauci, MD. “The findings from this study support the value of screening for toxoplasmosis to identify patients who could benefit from treatment.”
Currently available blood tests can determine whether a person has ever been infected with any strain of Toxoplasma parasite. The experimental test developed at NIAID improves upon the older tests because it can detect the presence of strain-specific antibodies that distinguish infecting strains from one another. The test was developed by Michael Grigg, PhD, of NIAID’s Laboratory of Parasitic Diseases, and his colleagues. It was applied to blood samples collected between 1981 and 2009 as part of the National Collaborative Chicago-Based Congenital Toxoplasmosis Study. The study of congenitally infected children was initiated by NIAID grantee Rima McLeod, MD, of the University of Chicago, who is the first author of the new study, published online in Clinical Infectious Diseases.
At least 15 distinct T. gondii strain types have been found throughout the world. In France, where research has been done to establish which strains are most common, a strain called type II predominates. Type II parasites can be distinguished from all other strains, which are collectively termed not exclusively type II strains (or NE-II).
Using the new test, the researchers found evidence of either type II or NE-II infections in 183 of the mother-child pairs in the national congenital toxoplasmosis study. Statistical analysis revealed that 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. For example, severe eye damage was seen in 67% of NE-II cases (59 out of 88), while such eye damage was present in only 39% of type II cases (18 out of 46). The researchers noted, however, that the association is not absolute, and that mild, moderate or severe disease can result regardless of the infecting strain.
Source: The National Institutes of Health
