Natural infection by simian retrovirus-6 (SRV-6) in Hanuman langurs (Semnopithecus entellus) from two different geographical regions of India.

We have previously reported natural infection of Hanuman langurs (Semnopithecus entellus) from Lucknow, India by a novel simian retrovirus, SRV-6, a beta-retrovirus (type D retrovirus). Here we describe infection by a closely related SRV-6 in an isolated feral population of Hanuman langurs from Jodhpur in the Northwestern desert region of India. Serological analyses, using in-house ELISA and WB, genomic amplification, and sequencing of env region (gp70 and gp20) of the viral genome were carried out. SRV-6-infected langurs from the two regions were serologically cross-reactive. The env gene was used for phylogenetic analyses, being the most variable part of a retroviral genome. The surface glycoproteins (gp70) were almost identical between the two SRV-6 isolates and related to but distinct from equivalent regions from other exogenous SRVs. We could sequence the transmembrane glycoprotein gp20 from SRV-6 infecting the Jodhpur langurs, which was again shown to be related to but unique compared to the other known SRVs. The study suggests that natural infection by related strains of SRV-6 occurs in wild langurs from different parts of India.