Border disease without nervous signs or fleece changes
Bonniwell, M.A.; Nettleton, P.F.; Gardiner, A.C.; Barlow, R.M.; Gilmour, J.S.
Veterinary Record 120(11): 246-249
1987
ISSN/ISBN: 0042-4900 PMID: 3576934 Document Number: 299447
A natural infection with border disease virus occurred in a flock on low ground in Argyll in the spring of 1984. The outbreak was unusual in that the typical clinical signs of border disease, i.e. tremor and, or, fleece changes were not present; manifestations of disease were restricted to abortion and the birth of small weak lambs. The disease was shown to have been introduced to the flock by four ewes persistently infected with border disease virus among a group of 39 purchased in October, 1983. Further investigations in late August 1984 detected viraemia in six of seven lambs that were not thriving and four of 24 apparently healthy lambs. Attempted 'natural vaccination' of susceptible sheep by mixing them at grass for three months with groups of ewes and lambs known to contain virus excretors was largely unsuccessful as only four of 22 'sentinel' sheep seroconverted. In October 1984 the persistently infected purchased animals and all that year's lamb crop were removed from the farm. No disease occurred in 1985 when the lambing percentage was 129% compared with 100% in 1984. Two of the four persistently infected purchased ewes were mated at Moredun Research Institute in December 1984 and both produced healthy but persistently infected lambs.