Full-length genome sequence analysis of enzootic nasal tumor virus isolated from goats in China

BACKGROUND: Enzootic nasal tumor virus (ENTV) is a betaretrovirus of sheep (ENTV-1) and goats (ENTV-2) associated with neoplastic transformation of epithelial cells of the ethmoid turbinate. Confirmation of the role of ENTV in the pathogenesis of enzootic nasal adenocarcinoma (ENA) has yet to be resolved due to the inability to culture the virus. Very little is known about the prevalence of this disease, particularly in China. METHODS: To evaluate the genetic diversity of ENTV-2 from Shaanxi province of China, the complete genome sequence of four isolates from Shaanxi province was determined by RT-PCR. These sequences were analyzed to evaluate their genetic relatedness with other small ruminant betaretroviruses. Phylogenetic analyses based on the gag gene and env gene were performed. RESULTS: The ENTV-2-Shaanxi1 genome shared 97.0% sequence identity with ENTV-2-SC (accession number HM104174.1), and 89.6% sequence identity with the ENTV-2 sequences (accession number AY197548.1). ENTV-2 is closely related to the ENTV-1 and jaagsiekte retrovirus (JSRV). The main sequence differences between these viruses reside in LTR, two small regions of Gag, Orf-x, and the transmembrane (TM) region of Env. A stretch of 6 consecutive proline residues exists in VR1 of the ENTV-2-Shaanxi1 ~ 4 isolates. All the ENTV-2-Shaanxi isolates have the YXXM motif in the cytoplasmic tail of the Env. Phylogenetic analysis by nucleotide sequences showed that ENTV-2-Shaanxi1 ~ 4 isolates were closest related to two ENTV-2 isolates published in NCBI, especially with ENTV-2-SC strain. CONCLUSIONS: This finding indicates that ENA most likely was introduced to Shaanxi province by the movement of contaminated goats from other areas in China. This study adds to understand the circulation, variation and distribution of ENTV-2, and may prove beneficial in future control or eradication programmes.