ORIGINAL PAPER Molecular and virulence characterization of Toxoplasma gondii strains isolated from humans in Portugal Anabela Vilares 1 & Maria João Gargaté 1 & Idalina Ferreira 1 & Susana Martins 1 & João Paulo Gomes 2,3 Received: 5 December 2016 /Accepted: 10 January 2017 # Springer-Verlag Berlin Heidelberg 2017 Abstract Toxoplasma gondii is an apicomplexan parasite re- sponsible for toxoplasmosis which infects all warm-blooded vertebrates, including mammals and birds. The majority of studies conducted in Europe have revealed that more than 80 % of strains isolated from human infections belong to genotype II, whereas genotypes I and III are responsible for a small number of cases. Atypical and recombinant strains are generally associated with more severe infections. In Portugal, there is a lack of data concerning genetic diversity as the classical typing studies in humans have never been performed. We aimed to determine the Sag2 and microsatellite-based (TUB2, TgM-A, W35, B17, B18) genotypes of T. gondii iso- lated from humans in Portugal, as well as to study their viru- lence in mice. We analyzed 48 strains from congenital and acquired toxoplasmosis collected during the last two decades. Sag2-based genotyping of T. gondii was achieved in all 48 strains where 35 (73 %) were classified as type II and 13 (27 %) were type I. The multilocus PCR of five microsatellites allowed the classification of 10 strains (21 %) as recombinant strains that had been previously identified as type II or I by Sag2 typing. Seven out of the 48 strains, including three type I, three recombinant, and one type I, were virulent in mice. This study constitutes the first evidence of recombinant strains circulating in Portugal in humans from congenital infection, highlighting the need for a better evaluation of these strains as their phenotype is still barely understood. Keywords Toxoplasma gondii . Genotype . Recombinant . Strain . Congenital Introduction Toxoplasma gondii is an obligate intracellular protozoan par- asite which is responsible for toxoplasmosis in different spe- cies of birds and mammals, including humans (Dubey 2010). Infections in healthy adults are generally benign, although toxoplasmic retinitis is a frequent cause of serious eye disease in otherwise healthy adults (Gilbert et al. 1999). More pro- found disease occurs in immunocompromised hosts (Luft and Remington 1992) or as the result of congenital infections (Hohlfeld et al. 1989). The primary infection during pregnan- cy is asymptomatic to mother and sometimes to the fetus; however, a new born deprived of treatment may develop later symptomatology with recurrent ocular toxoplasmosis, which may lead to blindness and neurological problems during child- hood and adolescence (Dubey 2010; Groër et al. 2011; Horacek et al. 2012; Montoya and Liesenfeld 2004; Tedla et al. 2011; Zhou et al. 2011). The determinants of disease severity are not well understood, although a variety of factors including host genotype, nutrition, immune status, infection load, and parasite genotype have been suggested to influence the outcome of infection (Sibley et al. 2002). Electronic supplementary material The online version of this article (doi:10.1007/s00436-017-5374-5) contains supplementary material, which is available to authorized users. * Anabela Vilares anabela.vilares@gmail.pt 1 National Reference Laboratory of Parasitic and Fungal Infections, Department of Infectious Diseases, National Institute of Health Dr. Ricardo Jorge, Av. Padre Cruz, 1649-016 Lisbon, Portugal 2 Research and Development Unit, Infectious Diseases Department, National Institute of Health Dr. Ricardo Jorge, Av. Padre Cruz, 1649-016 Lisbon, Portugal 3 Bioinformatics Unit, Infectious Diseases Department, National Institute of Health Dr. Ricardo Jorge, Av. Padre Cruz, 1649-016 Lisbon, Portugal Parasitol Res DOI 10.1007/s00436-017-5374-5