Serological diagnosis of Chagas disease with purified and defined Trypanosoma cruzi antigens.

Chagas disease is caused by the protozoan parasite Trypanosoma cruzi, widespread in the American Continent. A recent report of the World Health Organization estimated that 16-18 million people are currently infected and that about 90 million individuals living in endemic areas are at risk of contracting T. cruzi infection. The high prevalence and continental extension of Chagas disease in Latin America, as well as the constant migration of T. cruzi infected individuals to non-endemic areas, require efficient and practical diagnostic procedures (Schmunis 1991,Wendel & Gonzaga 1993). Chagas disease is characterized by the chronological appearance of specific classes of antibodies during the development of the infection. Antibodies from IgM class first appears as a typical sign of the acute phase of the disease, and there are some reports of an increase of total and specific IgA antibody class at this early phase (Lorca et al. 1995, Umezawa et al. 1996a). Antibodies of the IgG class, already present in the acute phase, accompanies the infection until the chronic phase. Detection of antibodies against T. cruzi antigens by serological methods is still the main support for diagnosis of Chagas disease. The commercial available diagnostic tests are based on the whole or semi-purified antigenic fractions from T. cruzi epimastigote (the non-infective forms of the parasite). Considerable variation in the reproducibility and reliability of these tests have been reported by different laboratories, mainly to crossreactivity with other pathogens and standardization of the reagents (Camargo et al. 1986). Diagnostic tests employing epimastigote antigenic extract have a limited specificity, associated to the fact of they do not possess highly reactive epitopes for IgG/IgM antibodies present in patients with acute or congenital Chagas disease (Umezawa et al. 1996a-c). The epimastigote antigenic fraction is constituted by complex molecules, that favors the appearance of false positive reactions and cross reaction with sera from patients with another infections, mainly visceral leishmaniasis (Chiller et al. 1990). This antigenic heterogeneity does not allow the differential diagnosis between the acute and chronic phases, and also among the clinical manifestations of Chagas disease.