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From issue 2646 of New Scientist magazine, 08 March 2008, page 12-13

 EU puts farmers in a bluetongue catch-22

  • 08 March 2008
  • From New Scientist Print Edition.
  • Debora Mackenzie

 

TINY biting flies are emerging across Europe this week as spring returns. At 15 C, any bluetongue virus they are carrying will start replicating, and the disease will spread. Unless sheep and cattle in its path are vaccinated it could ravage Europe's sheep flocks.

But it seems unlikely there will be enough vaccine to stop the virus spreading. What's more, European Union regulations mean what vaccine there is cannot be used to stop it invading new areas.

Cold winters used to keep the disease out of temperate countries, but an African strain of bluetongue called BTV8 appeared in Belgium in 2006 and moved into all of Benelux and part of Germany and France (see Map). In the second half of 2007 it spread so far that even the north coast of Spain was affected. Animal health experts expect it to spread even further this year.

That will happen if we don't vaccinate enough cattle, says Philip Mellor of the Institute for Animal Health at Pirbright in the UK. "It replicates massively in cattle and spreads to many more midges, amplifying the infection." BTV8 doesn't kill cattle, though it slows their growth and saps milk production and fertility.

It does kill European breeds of sheep, however. At last year's rate of spread it will soon invade northern England, Wales and Scotland, which have far higher densities of sheep than any part of northern Europe hit so far.

Five companies hope they can start delivering doses of BTV8 vaccine by May, when rising temperatures and elapsed incubation times mean spread of the infection will accelerate. But plant closures have delayed vaccine production, says Declan O'Brien of the International Federation for Animal Health in Brussels, Belgium, which represents vaccine makers, and countries have been slow to place orders. In May, England and Wales will get only the first 2 million of the 22.5 million doses they ordered for this year. Other European countries are in similar or worse positions.

Vaccines will be used only in "protection zones" (PZs) - sites within 100 kilometres of previous outbreaks - effectively where the virus is already present and where animals are most at risk. Under EU rules vaccine cannot be used in uninfected areas to keep the virus out.

The reasoning is that if the virus invades a new area sick animals will betray its presence. But as nothing can be done to keep midges out, the virus is virtually certain to spread, so such sentinels serve little purpose. "Vaccination should cover susceptible animals in the infected and adjacent, receptive areas," says Arnon Shimshony, a former chief vet for Israel, where bluetongue is endemic. "It is plainly ridiculous not to vaccinate outside the PZs," says Ruth Watkins, a clinical virology specialist and livestock farmer.

Mellor hopes that if most of the virus is in the middle of the PZs it may be enough to "keep rolling out the vaccinated area so animals just beyond the infected zone will be protected". With midges moving unpredictably, and limited disease tracking, that could be difficult. Besides, warns Watkins, "many farmers in the PZs are not ordering vaccine," as the programme is voluntary in England and farmers must pay.

"It would be nice to vaccinate all the animals in an uninfected area, and keep infected animals out until you do," says Mellor. But EU rules create a catch-22. "If you [start to] vaccinate you immediately become a PZ. So animals can be shipped to you from another PZ," meaning virus will likely be brought to your area.

This seems to be one reason sheep-intensive Scotland - which is independent from England for animal health - resisted ordering vaccine until this week, so it is unlikely to get any until autumn. If it vaccinates, it becomes a PZ and gets infected animals. If it doesn't, it can exclude infected animals but risks getting bluetongue if infected midges arrive. "It would make sense to wait and vaccinate quickly if it gets close," says Mellor.

Scotland may not have vaccine in time if the virus moves fast. Mellor and O'Brien say the European Commission may consider changing the rules.

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