Toxoplasma strain type and human disease: risk of bias during parasite isolation?

A recent publication has described for the first time the use of restriction analysis directly on biological samples to show the high frequency of multiple Toxoplasma gondii infection in individual patients. However, no mixed infection has been reported in other studies, and no cases have yet been identified either by inoculation of mice or in vitro culture. Here, we discuss the possibility that the parasite isolation process could represent a risk of bias in the type determination of the Toxoplasma strain responsible for infection.