Parasitol Res (2006) 99: 7–13 DOI 10.1007/s00436-005-0122-7 ORIGINAL PAPER Marta Bértoli . Miriam Hitomi Andó . Max Jean De Ornelas Toledo . Silvana Marques De Araújo . Mônica Lúcia Gomes Infectivity for mice of Trypanosoma cruzi I and II strains isolated from different hosts Received: 22 March 2005 / Accepted: 18 November 2005 / Published online: 31 January 2006 # Springer-Verlag 2006 Abstract In this paper, the infectivity for mice of Trypanosoma cruzi I and II strains isolated from sylvatic animals, triatomines, and humans is determined using fresh blood examination, hemoculture, culture of macerated or- gans, and polymerase chain reaction (PCR). Six strains were considered to have low infectivity (9.1–18.2%), five medium (27.3–45.4%), and one high (100.0%). Infectivity of T. cruzi strains isolated from sylvatic animals was sig- nificantly higher than that of strains isolated from humans and triatomines (p=0.0141). No significant difference was observed between the infectivity of T. cruzi I and II strains. The parasite was detected by fresh blood examination in one strain, by hemoculture and culture of macerated organs in four strains, and by PCR in all strains. We conclude that the infectivity is related to the host from which the strains were isolated, but the infectivity is not related to the genetic group of the parasite. We also conclude that the majority of the strains studied have low and medium infectivity for mice, and that PCR is an important tool to detect T. cruzi in strains with this biological characteristic. Introduction American trypanosomiasis is one of the most important endemic infections in Brazil and Latin America. It is estimated that 16–18 million people are infected, and that 120 million people on the continent are at risk of becoming infected (Moncayo 1999). Approximately 3.5 million peo- ple in Brazil are infected (Dias 1997), and in the southern region of the country, infection by Trypanosoma cruzi in humans has been proven to be endemic in the states of Rio Grande do Sul and Paraná. The latter is considered to be the state with the fourth-highest rate of the disease in the country, with a prevalence of 4% (Camargo et al. 1984; Silveira and Resende 1994). Studies have shown that T. cruzi strains consist of a variety of subpopulations, each with different character- istics, and that natural populations of T. cruzi show a large degree of biological, biochemical, immunological, and genetic heterogeneity (Araújo and Chiari 1988; Carneiro et al. 1991; Brener 1992; Oliveira et al. 1997; Gomes et al. 1998a). Infectivity for mice is one of the parameters used to study the biological behavior of T. cruzi strains. This can be demonstrated by fresh blood examination, hemoculture, and inoculation of macerated organs from infected animals, among other methods (Luquetti and Rassi 2000). One molecular method that has been used to confirm infection by T. cruzi in different hosts is polymerase chain reaction (PCR). There is agreement between various authors that this method is more sensitive than those usually used, such as hemoculture and xenodiagnosis (Ávila et al. 1993; Wincker et al. 1994, 1997; Britto et al. 1995; Gomes et al. 1998b; Castro et al. 2002; Meira et al. 2002). Trypanosoma cruzi strains are currently classified in separate phylogenetic lineages: T. cruzi I and T. cruzi II (Recommendations from a Satellite Meeting 1999). The T. cruzi I group is found more often in the sylvatic trans- mission cycle, whereas the T. cruzi II group is more commonly associated with the domestic transmission cycle and the chronic human disease (Toledo et al. 2004). A number of studies have shown differences between the two phylogenetic lineages in terms of virulence for mice, transmissibility by triatomines, infectivity for cell cultures, and drug sensibility in vitro (Laurent et al. 1997; Lana et al. 1998; Revollo et al. 1998; Toledo et al. 2002). The heterogeneity of each of these lineages, both in geo- M. Bértoli . M. H. Andó . M. J. De Ornelas Toledo . S. M. De Araújo . M. L. Gomes Departamento de Análises Clínicas, Parasitologia Básica, Universidade Estadual De Maringá, Maringá, Paraná, Brazil M. L. Gomes (*) Laboratório de Doença de Chagas, Departamento de Análises Clínicas-Universidade Estadual de Maringá, Avenida Colombo, 5790, 87020-900, Maringá, Paraná, Brazil e-mail: mlgomes@uem.br Tel.: +55-44-32614877 Fax: +55-44-32614490