An increase of Hantavirus Pulmonary Syndrome (HPS) cases around a southwestern Argentina town and in persons living 1400 km away but in contact with those cases was detected during the spring of 1996. In order to evaluate person-to-person transmission we compared the homology of PCR-amplified viral sequences of 26 Argentine and Chilean cases. Sixteen of them were epidemiologically linked cases and had the same sequence (Epilink/96) in the S segment 3' noncoding region and in the M segment partial G1 and G2 region (a total of 1075 nucleotides). Contrarily, two geographical and contemporary but nonepidemiologically related cases differed from Epilink/96 in the compared regions. No significant differences, such as glycosylation or hydrophilic pattern, were found between Epilink/96 and the other sequences. Nucleotide and deduced amino acid sequence homologies between samples from southern Argentina and Chile ranged from 90.9 to 100% and 96.4 to 100%, respectively. Phylogenetic analysis revealed that all the analyzed southwestern viruses belong to the Andes lineage. Although human infection principally occurs via inhalation of contaminated rodent excreta, our results with Andes virus show the first direct genetic evidence of person-to-person transmission of a hantavirus.

Epidemiologic and genetic data show that person-to-person spread likely took place during the prodromal phase or shortly after it ended.

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A fatal case of serologically confirmed hantavirus pulmonary syndrome (HPS) was recently reported in southwestern Argentina. Nucleotide sequence analysis of PCR fragments from conserved regions of the S and M genomic segments of the virus, amplified from RNA extracted from autopsy lung and liver tissues, showed the virus (referred as Andes virus) to be novel. Comparisons between Andes virus genome sequences with the corresponding sequences of the more closely related hantaviruses revealed differences at the amino acid level from 13.6 to 23.9% for G2 protein regions and from 8.5 to 12.5% for the amino terminal region of the nucleocapsid protein. Phylogenetic analysis using the maximum parsimony and maximum likelihood methods showed that Andes virus maps within the clade containing the HPS-associated viruses from North America. Within this group, Andes virus represents a unique lineage. This is, to our knowledge, the first report on the genetic characterization of a hantavirus from South America.