5 November 2008

Earlier this month the Central Veterinary Institute in the Netherlands reported that four outbreaks of bluetongue were not associated with bluetongue virus serotype 8 (BTV-8; widespread in northern Europe; the serotype that came to Great Britain in 2007) or serotype 1 (present in Spain and France; it has reached Brittany). Subsequent genetic analysis at the Institute for Animal Health's Pirbright Laboratory (an institute sponsored by the Biotechnology and Biological Sciences Research Council, BBSRC) revealed that the gene sequenced (gene 2, the one that determines the serotype of the virus) was typical of serotype 6 (BTV-6). This serotype had never previously been detected in Europe.

The sequence of gene 2 of the BTV-6 from the Netherlands was more than 99.9% the same as gene 2 of a live BTV-6 vaccine produced in the Republic of South Africa. This led to speculation that the source of the BTV-6 in the Netherlands might be illegally imported vaccine; only inactivated BTV vaccines are licensed in Europe.

 

In addition to genetic analysis, the blood sample from one of the Dutch farms (Heeten) affected by BTV-6 were tested for the presence of serotype-specific BTV antibodies at IAH Pirbright. If antibodies to any of the long-known 24 serotypes of BTV were present in the blood sample, the tests would identify the serotypes. On Friday 31 October, the Pirbright scientists reported* that the results of the antibody tests were "consistent with the cattle at Heeten having been infected with BTV-6 and either infection by or vaccination against BTV-8".

 

The vaccine made in South Africa, that contains live BTV-6, also contains four other serotypes of BTV. "However," reported the Pirbright scientists, "the absence of antibodies to multiple other serotypes in the blood samples from Heeten indicates that this animal at least had not received either of the multivalent vaccine preparations that are known to have been produced in South Africa."

 

Professor Peter Mertens of IAH said "We are currently sequencing all the genes of the Dutch BTV-6 to see if it is completely similar to the live vaccine strain." When an animal is simultaneously infected by two different serotypes of BTV, sometimes a virus is formed that has some genes from one serotype, and some genes from the other serotype. It is possible that the BTV-6 in the Netherlands is one such virus. The gene sequencing that is underway at IAH Pirbright will resolve the issue.

 

*ProMED Digest Saturday, November 1 2008 Volume 2008 : Number 471
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