Chagas' disease is an emerging and neglected disease in the Brazilian Amazon region, where T. cruzi I predominates among the acute cases of the disease; and T. cruzi III/Z3, a population cluster from sylvatic areas of the Amazon basin, is rarely associated with human infections. On 23rd April 2007, the Foundation for Health Surveillance of the State of Amazonas, Brazil reported an outbreak of acute Chagas disease in the municipality of Coari on the Solimões River banks. Fresh blood examination confirmed the infection in 25 patients. Parasite culture in LIT medium was successful for 18 isolates. Molecular characterization was performed by PCR of the non-transcribed spacer of the mini-exon and by sequencing of the mitochondrial cytochrome c oxidase subunit II (COII) gene. The T. cruzi isolates were all from genotype Z3, and sequencing revealed that all isolates had equal COII sequences compatible with TcIII type, suggesting a single source of infection. To our knowledge, this is the first outbreak of acute cases caused uniquely by the genotype TcIII/Z3. Wild vectors harbouring TcIII stocks contribute to transmission when the triatomine species reaches human food chain or when humans invade the forest environment, where sylvatic cycle constitutes a reservoir of parasites that might be associated with specific epidemiological and clinical traits of the emergent Chagas disease in the Amazon.
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