Characterization of human infection by <i>Leishmania</i> spp. in the Northwest of Argentina: immune response, double infection with <i>Trypanosoma cruzi</i> and species of <i>Leishmania</i> involved

<jats:p>The aims of this study were to characterize human American tegumentary leishmaniasis, which includes cutaneous, mucocutaneous and mucosal leishmaniasis, in Northwest Argentina, to determine the prevalence of double infection with <jats:italic>Trypanosoma cruzi</jats:italic> and to identify the species of <jats:italic>Leishmania</jats:italic> in this area. Most of the 330 leishmaniasis patients presented cutaneous ulcers (96·1%), 2·4% mucocutaneous and 1·5% the mucosal form (‘espundia’). The aetiological agents, determined by isoenzyme electrophoresis, were identified as <jats:italic>Leishmania</jats:italic> (<jats:italic>Viannia</jats:italic>) <jats:italic>braziliensis</jats:italic> in 16 out of 20 isolates and in the remaining 4 as <jats:italic>Leishmania</jats:italic> (<jats:italic>Leishmania</jats:italic>) <jats:italic>amazonensis</jats:italic>, the first ever-documented in Argentina. Sera analysed by ELISA and IFA using complex antigen from both <jats:italic>T. cruzi</jats:italic> and <jats:italic>L. braziliensis</jats:italic> showed a very high percentage of positives (66·3–78·2%). When antigens for specific diagnosis of Chagas' disease were used, 40·9% of the leishmaniasis patients were also found to be infected by <jats:italic>T. cruzi</jats:italic>. These results indicate that the strong immune response against <jats:italic>T. cruzi</jats:italic> gave no protection to <jats:italic>Leishmania</jats:italic>, in spite of the serological cross-reaction between these parasites. In addition, we showed that more than 40% of the patients would be misdiagnosed as chagasic if complex antigens, as epimastigotes or soluble fraction from epimastigotes, were used in IFA or ELISA. This is of paramount importance not only because patients' treatment would be associated to misdiagnosis but the fact that in many countries in Central and South America, a positive test for Chagas' disease means a rejection for those seeking employment.</jats:p>