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10 Jul 2008
Did the blue tongue virus strain that is currently spreading through Northern Europe (BTV-8) escape from a laboratory? There are scientists who believe this. Molecular biologist Dr. Piet van Rijn of the Central Veterinary Institute (CVI), part of Wageningen UR, has arguments that refute this belief, 'although you never know for sure'.
The discussion about the origin of the virus has been raging since the first Northern European sheep and cattle became infected in 2006. Very quickly, a link was made with a virus that was circulating in South Africa, and there were suggestions that the Northern European virus originated from vaccinations made in the field. With a recent publication in the online edition of Virology, British, French, South African, Belgian and Dutch scientists refuted this suggestion.
The genome of the North European virus was compared with that of various other known strains of BTV-8. The conclusion was that the virus is a new introduction that did not originate from a known BTV-8 vaccine. However, the actual origin of the virus remains unclear.
The discussion about the origin of the virus has not ended with the above publication. Another remarkable finding in the Netherlands has fuelled new speculation. The CVI has shown that it is plausible that the virus is not only transmitted by a small fly or midge from one animal to another, but also via the placenta of the mother to the unborn calf. And calves can also be infected with the virus via the colostrum. Moreover, together with the Animal Health Service, it was ascertained this spring that healthy, virus-carrying calves are regularly born from infected cows. And healthy, uninfected adults can become infected with the virus if they eat the placenta following the birth of a calf. Cows do this by their nature.
The idea that a virus in the field can pass through the placenta has not been accepted by everyone. The American professor James MacLachlan, from the School of Veterinary Medicine of the University of California, stated that this can only occur with laboratory strains. And the blue tongue virus does not have to pass through the placenta at all in order to reproduce, asserted MacLachlan.
According to Van Rijn, this infection route was probably not observed previously because the virus primarily maintains itself in areas where the vectors do not become inactive in the winter, such as the midge in Northern Europe. ‘In these areas, the passage through the placenta has little epidemiological significance. This is not the case in the Netherlands.’ / Jan Braakman
This article has been produced by the editors of Resource, the weekly news magazine of Wageningen University and Research Centre. More information can be obtained by the press department of Wageningen UR, e-mail: pers.communicatie@wur.nl or the editorial board of Resource, e-mail: resource@wur.nl. See also the archive on http://www.resource-online.nl
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