European farmers battling bluetongue, a viral disease infecting cattle, sheep, and goats, have something new to worry about. Four cows in the Netherlands have contracted a strain of the virus never before seen in Europe that was most likely introduced via the illegal use of a live vaccine, the Dutch ministry of agriculture announced on Tuesday. Experts worry that the virus might spread, which would complicate the fight against bluetongue.
Bluetongue, spread by tiny insects called biting midges, comes in 24 so-called serotypes, several of which are on the rise in Europe. A serotype called BTV1 is rapidly moving northward across France; another called BTV8, which probably originated in Africa, appeared on Dutch farms out of the blue in 2006 and has since spread as far as Sweden, Spain, the United Kingdom, and Hungary.
Last month, the Central Veterinary Institute (CVI) of Wageningen University in Lelystad, the Netherlands, discovered four animals from four farms that had come down with yet another bluetongue virus. A detailed genetic analysis at the Institute for Animal Health (IAH) in Pirbright, U.K., has now revealed that the outbreak is caused by serotype BTV6 and almost certainly caused by a live bluetongue vaccine produced by Onderstepoort Biological Products, a company in South Africa. The vaccine is used in Africa and the Middle East but is not registered in Europe. Most European countries are loath to use live bluetongue vaccines because of the risk that it may cause disease or mutate to become more virulent.
The Dutch agriculture ministry has ordered an investigation into the origin of the outbreak. Three of the farmers had vaccinated their cattle using a killed vaccine against BTV8. They most likely did not use the Onderstepoort vaccine themselves, CVI molecular virologist Piet van Rijn says, but their cattle could have become infected if other farmers in the region used it. There are possible routes, however, van Rijn adds; it may have been imported through infected or vaccinated animals, for instance.
The Onderstepoort vaccine--which the company sells for only goats and sheep--comprises three shots that together offer protection against 15 serotypes, including BTV6. How it might have ended up in Europe is unclear. "We have never, ever, ever shipped this vaccine to Europe," says the company's international sales manager, Jacob Modumo.
The question now is whether BTV6 is in Europe to stay. Because it was introduced late in the biting midge season and few animals appear to have become infected, van Rijn hopes that the virus won't survive the coming winter. If it does, and if it starts spreading, European farmers may have to vaccinate against BTV6 as well--not with the live vaccine but with a killed one.
Meanwhile, a Swiss research team has announced that it has discovered what looks like a new bluetongue serotype--the 25th. In a paper published online by Emerging Infectious Diseases, Martin Hofmann and his colleagues at the Institute of Virology and Immunoprophylaxis in Mittelhaeusern, Switzerland, report a genetic analysis showing that a virus discovered accidentally during routine BTV8 testing--and christened the Toggenburg Orbivirus--is probably a novel bluetongue serotype. To prove it, the team will have to verify that antibodies against the virus don't neutralize the 24 known serotypes and vice versa, Hofmann says; that has been impossible so far because the virus won't grow in cultured cells.
"To discover a new BTV is interesting, but to discover it in central Europe is most surprising," IAH virologist Peter Mertens said in a statement issued by his institute today. "This new BTV is so different from other ones that we cannot even guess where it came from." The good news is that the new serotype does not seem to cause any symptoms in goats and sheep, Hofmann says. Whether that's true for cattle is unclear.
The European Commission yesterday proposed to spend an extra €100 million on fighting bluetongue in 2009, on top of the €60 million already pledged. The measure has yet to be approved by the European Parliament and the member states.