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With the first cases recently reported in Germany, global warming could be one reason for the increasing spread of so-called West Nile virus in Central Europe. The virus, which originated in Africa, mainly infects birds, which can introduce it locally during their annual migration. It is transmitted by mosquitoes and can trigger the tropical disease West Nile fever in humans and horses. While infections are usually harmless in humans and can only cause fever, headaches and, in extreme cases, meningitis in the elderly and those with a compromised immune system, the disease is often fatal in horses and birds. Last year, birds that had died of West Nile virus were found for the first time in Germany. This is one of the current topics at this year’s Leipzig Veterinary Congress: the programme includes a lecture on 18 January by Dr Michael Sieg from Leipzig University’s Institute of Virology.

“In recent months, infections have been concentrated in Central Germany,” said Professor Thomas Vahlenkamp, Director of the Institute of Virology and Dean of the Faculty of Veterinary Medicine at Leipzig University. Several horses from this region were admitted to the University’s Department for Horses, where they were diagnosed with West Nile virus. Vahlenkamp pointed out that the virus, which is a notifiable animal disease, has already claimed the lives of numerous horses in Germany. “Humans are not a source of infection. Birds fall ill with it, and mosquitoes usually transmit the virus to horses and humans,” explained the veterinary virologist. He added that birds in the crow family are particularly at risk, and that eagle owls, flamingos and other species of owl had also been affected at the zoos in Leipzig and Halle.

Climate change may be contributing to the spread of the virus, even in Germany. If temperatures are only slightly higher, mosquitoes reproduce more rapidly, thus increasing the risk of infection with West Nile virus. “It is conceivable that infected mosquitoes hibernate here in rooms or stables before resuming their transmission of the virus in the spring,” said Vahlenkamp. At present there is no prophylactic treatment or vaccination available for humans to prevent infection with West Nile virus. Preventing mosquito bites wherever possible is the only way to avoid infection. Following a major outbreak in the US, several thousand people have died there of West Nile fever in recent years.
In addition to West Nile virus, Usutu virus is also gaining ground in Central Germany. Usutu virus was first detected in mosquitoes in Germany a number of years ago. This caused the deaths of many birds, affecting blackbirds and various species of true owl particularly badly. Humans can also be infected by Usutu virus, but the disease is only serious in rare cases.