Schmallenberg virus – is it present in South Africa?

Abstract

In July 2006, a case of two out of three lambs born to one ewe in a flock of 45 had signs that, in retrospect, were possibly consistent with Schmallenberg virus infection. This occurred in the Onderstepoort area (Gauteng Province) but a definitive diagnosis was not made. Then, in May 2008, a farmer in the Delmas area (Mpumalanga Province) reported that deformed lambs had been born to several ewes in the flock. Six of the approximately 50 mated ewes gave birth to lambs showing varying degrees of arthrogryposis, torticollis, kyphosis, mandibular brachygnathia and hydrocephalus. Of these, only two were born alive but they died within a few hours. Blood was collected from the ewes with deformed lambs, a random sample of ewes that had given birth to normal lambs and a lamb that was normal but had a twin that was deformed. The samples were tested for Wesselsbron and Akabane antibodies using a complement fixation test and a haemagglutination/haemagglutination inhibition test that were available at that time. Bluetongue virus antibodies were also tested for using a commercial Enzyme-linked immunosorbent assay (ELISA) test. All samples showed negative results for all diseases tested. At the time Rift Valley fever virus had not been diagnosed in that region for many years and so it was not included in the testing. It is unlikely that this was the cause as no liver pathology was detected on postmortem examination of the lambs and no adult ewes had died. The farmer reported that another farm just a few kilometres away experienced the same deformities in some of their lambs but this farm was not investigated. During investigation it was thought that the cause was possibly a new strain of Akabane virus, although there was no way to confirm it. However, with the recent discovery of the Schmallenberg virus, it is possible that this virus has been present in South Africa for at least the last four years without being identified.