The deadly livestock virus that has taken the Netherlands, Belgium, and Germany by surprise this month did not come from southern Europe, as researchers had suspected. A genetic analysis, announced yesterday, has shown that the Bluetongue virus almost certainly originated in Africa, deepening the mystery of how it reached northern Europe.
First seen in the Netherlands on 14 August, the virus, which infects ruminants and is transmitted by Culicoides biting midges, has spread to more than 70 farms in Belgium, the Netherlands, and Germany (ScienceNOW, 25 August). Bluetongue sickens primarily sheep and goats and is not harmful to humans. There are 24 known "serotypes" of the virus, and over the past 8 years, a handful of them had made dramatic incursions from Turkey and the Middle East into southern European countries such as Greece, Italy, Spain, and the Balkan nations. Hence, scientists had assumed that the disease's arrival in northern Europe marked another leap north from one of these areas.
The leap is much bigger than they thought. Frantic days of genetic testing, completed very early Saturday morning at the Institute for Animal Health (IAH) in Pirbright, United Kingdom, has revealed the virus to be of serotype 8, previously known to occur only in sub-Saharan Africa, South America, and the Indian subcontinent, says Peter Mertens, who heads IAH's arthropod-borne virus research group. Its genetic fingerprint is closest to that of a virus isolated in Nigeria in 1982, which means it almost certainly came from Africa, Mertens says.
But how? There's almost no traffic of ruminants between Africa and Europe, says epidemiologist Aline de Koeijer of the Central Institute for Animal Disease Control (CIDC) in Lelystad, the Netherlands. Perhaps an imported zoo animal was infected, she suggests; veterinary authorities in the affected countries are trying to track down possible culprits. An infected midge may also have hitched a ride on an airplane, as happens occasionally with malaria-infected mosquitoes. Yet it would then have to find its way to a farm. The current outbreak is unusual in that some cows have gotten sick--normally, they are infected without clinical symptoms--but it's unclear whether this is typical of serotype 8, which has been studied very little, says CIDC virologist Eugène van Rooij.
Once introduced, the virus may have benefited from the warm weather, which speeds up its life cycle, says medical and veterinary entomologist Willem Takken of Wageningen University in the Netherlands; July was the hottest month on record in the affected areas. Scientists are certain that the outbreak will subside as temperatures drop; they can only hope that the northern European winter will kill off all infected midges and prevent a 2007 sequel.