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Further Strain in Belgium

12 February 2009

BELGIUM - The UK Institute for Animal Health (IAH), as the Bluetongue Reference Laboratory for the EU and OIE (World Organisation for Animal Health), has demonstrated that a cow in the Flanders region of Belgium had been infected with bluetongue virus serotype 11 (BTV-11).

"This is significant as it is the first evidence of the presence of serotype 11 anywhere in Europe", say the IAH. This is the fourth BTV serotype to be known to have been introduced into northern Europe since the first known introduction in 2006; the others are serotypes 1, 6 and 8.

"Whilst BTV-1 came from North Africa into southern Spain, then up Spain and into France, reaching as far as Brittany last year, we do not know how serotypes 6, 8 and 11 arrived. None of the latter three serotypes had previously been detected anywhere in Europe; they are normally resident on other continents. For example, the nearest known relative of the BTV-8 that arrived in northern Europe in 2006, and reached Britain in 2007, was in Nigeria", reported the IAH.

BTV is transmitted by biting midges of the genus Culicoides. Although these can be blown long distances e.g. across the English Channel from the Continent, or northwards over the Mediterranean Sea to southern Europe from North Africa, wind cannot be the mechanism of spread from sub-Saharan Africa; the distances are too great and the atmospheric conditions inappropriate for the survival of the midges.

The Belgian cow had been routinely sampled in November and analysed for evidence of bluetongue infection by CODA, the Belgian Reference Laboratory. Testing in CODA with a polymerase chain reaction (PCR) test able to detect all 25 serotypes of BTV (group-specific PCR test) indicated that the animal had been infected with BTV. However, the samples tested negative with serotype-specific PCR assays for serotypes 1, 8 and 6, the serotypes known to be present in northern Europe.

Samples were then sent to the Bluetongue Reference Laboratory at IAH Pirbright for further, comprehensive analysis. IAH first confirmed the presence of BTV with a group-specific test. Serotype-specific PCR tests for the seven serotypes of BTV known to be present in Europe, including southern Europe (1, 2, 4, 6, 8, 9 and 16) were negative, suggesting that the Belgian virus might a serotype new to Europe.

Further PCR tests were done using reagents specific to each of the 25 serotypes of BTV. These tests, and gene sequencing, showed that the Belgian virus was BTV-11. Another test showed that the Belgian serum contained antibodies against BTV-11, confirming the PCR tests; the animal had been infected with BTV-11.


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