Congenital Toxoplasmosis and Reinfection during Pregnancy: Case Report, Strain Characterization, Experimental Model of Reinfection, and Review

Wepresentacaseofdisseminatedcongenitaltoxoplasmosisinanewbornborntoamotherwhohadbeenimmunized against toxoplasmosis before conception. The mother was reinfected, likely by ingestion of imported raw horse meat during pregnancy. This clinical presentation is exceptional in France and raised the possibility of infectionbyahighlyvirulentToxoplasmastrain.Thestrainresponsiblewasisolatedfromtheperipheralbloodof the newborn, and when genotyped with microsatellite markers, it exhibited an atypical genotype, one which is very uncommon in Europe but had been described in South America. We tested the hypothesis of a reinfection with a different genotype by using an experimental mouse model, which confirmed that acquired immunity against European Toxoplasma strains may not protect against reinfection by atypical strains acquired during travel outside Europe or by eating imported meat. After primary maternal infection by Toxoplasma gondii during gestation, the parasite may enter the fetal circulation by infection of the placenta. Placental transmission is less frequent when infection is acquired before the tenth week of pregnancy and is very rare when infection is acquired before conception. Without treatment, the incidence of fetal infection is 10%–15% for acquisition during the first trimester, 30% for the second trimester, and 60% for the third trimester [1]. Early maternal infection (during the first and second trimester) may result in severe congenital toxoplasmosis, including fetal death and spontaneous abortion. By contrast, late maternal infection (during the third trimester) usually results in subclinical toxoplasmosis in newborns. In these cases, infection initially goes unnoticed, but these babies can develop chorioretinitis during later life [2]. Acute infection is followed by the formation of cysts in chronic infection and is associated with an immune response that usually confers protection against reinfection. This chronic infection is characterized by stable titers of specific IgG. In immunocompetent mothers who have been immunized against toxoplasmosis before conception, immune mechanisms prevent transmission of the infection to their fetuses. We report a case of life-threatening, disseminated congenital toxoplasmosis in an infant born to an immunocompetent mother who had been immunized against toxoplasmosis before conception. We also isolated and characterized the strain that caused the infection.