Detection of antibodies against Bluetongue virus among domestic ruminants in the highlands of Nepal.

Abstract

Bluetongue (BT) is one of the most economically important transboundary animal diseases. In recent years, it has been considered a disease related to climate change. A study was undertaken in 2013 in Nepal to measure the prevalence of Bluetongue virus (BTV) infection among domestic ruminants inhabiting the 3 agro-climatic zones with altitudes ranging from 150 to 2,400 metres above sea level. Twelve clusters representing the 3 altitudes were selected. The presence of antibodies against BTV was demonstrated in serum samples of sheep, goats, cattle, buffaloes, yaks/chauries, and chyangra goats (Himalayan goat) of Nepal. For this purpose, a total of 2,084 sera were collected from a population of 202 sheep, 739 goats, 590 cattle, 379 buffaloes, 105 yaks/chauries, and 69 chyangra goats between February 2013 and January 2014. The presence of antibodies against BTV was investigated using competitive enzyme-linked immunosorbent assay (c-ELISA). Of the 2,084 collected sera, 45.20% were positive for BTV antibodies. Species-wise prevalence was 17.82%, 47.50%, 53.05%, 58.05%, 7.62%, and 20.29% in sheep, goats, cattle, buffaloes, yak, and chyangra goats, respectively. Contrary to the general belief, maximum numbers of seropositive cases were recorded in buffaloes followed by cattle, goats, chyangra goats, sheep, and yak/chauries. The samples collected in the post-monsoon period (July-August is the monsoon period) show a seroprevalence higher than the pre-monsoon samples. This study shows the seroprevalence of BT in domestic ruminant population of Nepal at all altitudes. The highest prevalence has been reported in the plains of Terai followed by gradual decline in the mid-hills, and in the high mountains. Furthermore, detection of antibodies against BTV in both small and large ruminants (chyangra goats and yak/chauries) dwelling in high altitudes in the absence of BT vaccination is suggesting vector movement to the highlands as a consequence of warmer climate. These findings suggest that the climatic conditions, even at the higher elevation, are suitable for the survival of biting midges responsible for the transmission of BTV.