An Investigation into the Prevention of and Transmission of Pestivirus in Sheep in Australia

Prell, Madeleine
Charles Sturt University


Border disease virus is a member of the pestivirus genus that primarily affects sheep, causing
reproductive losses through abortion, still births and the birth of weak lambs. The key characteristic of
this disease is the birth of persistently infected (PI) lambs which, after surviving transplacental
infection, are born antibody negative, yet antigen positive, and thus shed the virus for their entire life
and are the primary source of spread within a flock. The cornerstones of BDV control are, detection
and elimination of PI calves or lambs, biosecurity measures to prevent re-infection and surveillance
programs. Recommendations for control of BDV in sheep are greatly centred around the approach to
bovine viral diarrhoea virus (BVDV), the highly prominent cattle pestivirus species, due to a lack of
specific research into BDV control and elimination. In this study two aspects of a BDV control program
were investigated; the cross effectiveness of the BVDV-1c vaccine, Pestigard®, and the rate of
seroconversion in a flock deliberately exposed to known PI lambs. The vaccine appeared to be safe,
and the optimal dose was the full cattle dose (2 mL). While vaccination induced markedly high virus
neutralising titres to BVDV when administered a quarter, half and full dose registered for cattle, the
BDV titres achieved were low and unlikely to prevent transplacental infection. After a maximum of 15
days exposure to two PI lambs in confined conditions, only 3 of 74 previously naïve sheep
demonstrated seroconversion. This demonstrated a very low rate of transmission and suggested that
deliberate exposure to PI lambs at low-risk times was not likely to be an effective means of achieving
seroconversion throughout a flock and thus provide protection against BDV challenge during gestation.