Evidence for transplacental and contact transmission of bluetongue virus in cattle

Abstract

This paper presents evidence that a field strain of bluetongue virus serotype 8 (BTV-8) was transmitted transplacentally and that it was also spread by a direct contact route. Twenty pregnant heifers were imported from the Netherlands into Northern Ireland during the midge-free season. Tests before and after the animals were imported showed that eight of them had antibodies to bluetongue virus, but no viral RNA was detected in any of them by reverse transcriptase-PCR (RT-PCR). Two of the seropositive heifers gave birth to three calves that showed evidence of bluetongue virus infection (RT-PCR-positive), and one of the calves was viraemic. Two further viraemic animals (one newly calved Dutch heifer, and one milking cow originally from Scotland) were also found to have been infected with BTV-8 and evidence is presented that these two animals may have been infected by direct contact, possibly through the ingestion of placentas infected with BTV-8.

Bluetongue in Europe: past, present and future

“…Four of the heifers then calved, and retesting a few days later showed that three calves and two antibodynegative heifers now tested positive by PCR, indicating recent infection. These results indicated that BTV transmission had been able to occur despite the apparent absence of an infection source and the lack of Culicoides vectors, as confirmed by a light trap operated throughout the period in the same building, and was the first indication that vertical and horizontal (oral) transmission of this strain might be possible (Menzies et al 2008), a finding that was supported by several subsequent studies (e.g. De Clerq et al…”

“…Although the secondary routes described above are likely to be of minor significance during normal transmission, they may become disproportionately important for the survival of the virus when normal transmission is interrupted by cold weather , and one or more of these mechanisms is likely to be responsible for the handful of BTV transmission events confirmed to have occurred during the winter in NW Europe (e.g. De Hoffmann et al 2008;Menzies et al 2008).…”

Transplacental infection in goats experimentally infected with a European strain of bluetongue virus serotype 8

“…Documented transplacental infection and associated defects vary widely in sheep and cattle and is therefore unpredictable (Osburn, 1994;Maclachlan et al, 2000). Furthermore, in not all cases where animals were born either viraemic and/or PCR positive during the European outbreak of BTV-8 were nervous system lesions observed (De Clercq et al, 2008;Menzies et al, 2008;SantmanBerends et al, 2010;Saegerman et al, 2010). It is possible that neurological lesions may have become apparent if the infected foetuses were allowed to have developed to term.…”

“…The high frequency with which the BTV-8 strain was able to cross the placenta may have been a contributing factor that allowed the virus to persist during the adult vector free/low European winters. Several studies conducted in northwestern Europe have demonstrated the birth of seemingly healthy PCR positive and/or viraemic lambs or calves, some of which tested positive for viral RNA for several months (De Clercq et al, 2008;Menzies et al, 2008;Santman-Berends et al, 2010;Saegerman et al, 2010). These animals may have served as a source of virus for newly emerged adult midges in subsequent vector seasons.…”

Evaluation of commercial ELISA kits for the detection of antibodies against bluetongue virus

“…The virus is transmitted by specific species of Culicoides midges, family Ceratopogonidae (MacLachlan 1994). An evidence for transplacental and contact transmission of BTV was also described (Menzies et al 2008).…”