Leishmania (Viannia) braziliensis is the main cause of highly disfiguring mucocutaneous leishmaniasis (MCL) in South America. The related species L. (V.) peruviana has only been identified in simple cutaneous lesions (CL). Hybrids between L. braziliensis and L. peruviana have been reported although genetic exchange in Leishmania is considered to be rare. Here we compared growth in vitro, adaptive capacity under thermal and oxidative stress and behaviour in a hamster model, of L. braziliensis, L. peruviana, and their putative hybrids. At 24°C, the optimal temperature for in vitro growth, L. braziliensis had the highest growth rate. In in vitro studies hybrid clones presented heterogeneous phenotypes, from slower growth rates, similar to L. peruviana, to higher growth rates, as observed in L. braziliensis. Hamsters infected with hybrid strains, presented the highest parasite densities and aggressive relapses at a later stage of infection. Hybrids generally presented higher plasticity and phenotypic diversity than the putative parental species, with potential eco-epidemiological implications, including an impact on the success of disease control.

A panel of microsatellites mapped to the Leishmania genome might make it possible to find associations between specific loci and phenotypic traits. To identify such loci, a Perl programme was written that scans the sequence of a genome and writes all loci containing microsatellites to a MySQL database. The programme was applied to the sequences of the L. braziliensis, L. infantum and L. major genomes. The database is publicly available over the internet: http://www.genomics.liv.ac.uk/tryps/resources.html ‘Microsatellite Locus Extractor’, and allows the selection of mapped microsatellites that meet user-defined criteria from a specified region of the selected genome. The website also incorporates a primer design pipeline that will design primers to amplify the selected loci. Using this pipeline 12 out of 17 primer sets designed against the L. infantum genome generated polymorphic PCR products. A tailed primer protocol was used to label all microsatellite primers with a single set of labelled primers. To avoid the culture of parasites prior to genotyping, sets of nested PCR primers were developed to amplify parasite DNA eluted from microscope slides. The limit of detection was approximately 1·6 parasite equivalents. However, only 6/56 DNA from slides stored at ambient temperature for over 6 months gave positive PCR results.