Identification of a novel subtype of South River virus (family Bunyaviridae)

We previously reported the isolation of South River virus (SORV) from a pool of mosquitoes collected in the Yucatan Peninsula of Mexico (Farfan-Ale et al. in Vector Borne Zoonotic Dis 10:777-783, 5). The isolate (designated SORV-252) was identified as SORV after a 197-nucleotide region of its small RNA genome segment was sequenced. In the present study, the complete small and medium RNA genome segments and part of the large RNA genome segment of SORV-252 were sequenced and shown to have 92%, 85% and 90% nucleotide sequence identity, respectively, to the homologous regions of the prototype SORV isolate (NJO-94F). To determine the antigenic relationship between SORV-252 and NJO-94F, cross-plaque reduction neutralization tests (PRNTs) were performed using sera from mice inoculated with these viruses. SORV-252 and NJO-94F were distinguishable in the cross-neutralization assays; there was a twofold difference in the PRNT titers in one direction and a fourfold difference in the other direction, suggesting that SORV-252 represents a novel subtype of SORV. Additionally, SORV-252 and NJO-94F have distinct plaque morphologies in African green monkey kidney (Vero) cells. In conclusion, we provide evidence that a novel subtype of SORV is present in the Yucatan Peninsula of Mexico.