Bluetongue: strategy and success
2007 saw the disease caused by bluetongue virus (BTV) arrive in the UK. Whereas other diseases, such as rinderpest, have long been eradicated from Europe and others like foot-and-mouth remain unwelcome but infrequent visitors, this was the first time that bluetongue, an entirely new condition, was seen in British sheep and cattle.
Working with the Met Office, scientists at the Institute for Animal Health (IAH, an institute of BBSRC) had forecast correctly that easterly winds on the night of August 4-5 could have brought bluetongue virus-infected midges to East Anglia from Belgium. Surveillance was intensified in the area. Subsequently BTV-infected cattle were discovered and control measures taken to limit the spread of the disease.
IAH bluetongue experts advised Defra and the EU that vaccination was the only sustainable way of controlling the disease. A new vaccine was gradually made available by vaccine manufacturers during 2008. IAH scientists, including entomologists and mathematical modellers, identified the most at-risk areas in Britain, and advised Defra accordingly so that the limited quantities of vaccine could be utilised to best effect.
This strategy worked; there were no cases of bluetongue in the UK during 2008, saving an estimated £460M and 10,000 jobs in Britain’s livestock sectors, even though some bluetongue virus-infected animals had been imported. In contrast, France and Germany had reported 24,000 and 2,500 new outbreaks, respectively, by November 2008. The disease had spread faster than the vaccination programme, which emphasised the need for a timely and extensive vaccination strategy.
Bluetongue virus can cause mortality in excess of 10%. Image: IAH
Research in Northern Ireland and at IAH revealed that the BTV in question (type 8) could be transmitted from pregnant cattle (which had recovered from an earlier infection) to their unborn calves. Moreover, these calves were born healthy but with the virus in their blood stream. These calves were a risk factor; if Culicoides midges fed on them they would transmit the virus to other animals. As many cattle are pregnant over the winter, this was a way in which the virus could survive through the winter period, when midges are not active.
This knowledge led IAH scientists to advise farmers not to import sheep and cattle from bluetongue-affected areas on the continent, where the incidence of disease was high. Research had previously shown that infected sheep can also transmit the virus to their unborn young.
Extensive vaccination of animals in France in the winter of 2008-09, supported by vaccination in Britain, care over imports, and post-import testing by IAH, resulted in there being no cases of the disease in the UK in 2009.
Computer generated image of the bluetongue virus. Image: IAH
IAH is the Reference Laboratory (a major expert diagnostic facility) for Defra and the World Organisation for Animal Health (OIE) on bluetongue; it isolates and analyses the different strains of BTV that circulate around Europe.
There are 25 serotypes of BTV and each one needs a different vaccine. Efforts are being made to develop bivalent vaccines that will work against more than one strain, BTV-1 and BTV-8, for example.