What Is Bluetongue? Denmark Reports Cases of Insect-Borne Viral Disease

Denmark on Tuesday confirmed several cases of bluetongue disease, a non-contagious, insect-borne viral disease, in the eastern regions of the country.

The virus—known as the bluetongue serotype 3 or BTV-3—is transmitted by midges, a type of small fly that thrives in warmer weather. The viral infection, while harmless to humans, poses a serious threat to livestock such as sheep, cows and goats. While sheep are worst affected by the virus, cows are considered the main mammal reservoir.

Experts warn that the virus could rapidly spread across Denmark, posing a significant risk to livestock. Symptoms in infected animals include high fever, mouth ulcers, swelling of the face and tongue and a distinctive blue discoloration of the tongue—known as cyanosis—due to oxygen deprivation.

In addition to these symptoms, infected animals may also suffer from respiratory difficulties and reduced milk production, though the milk remains safe for human consumption.

Newsweek reached out to the Danish Veterinary and Food Administration via online form on Tuesday for comment.

In recent weeks, the virus steadily moved northward through Europe before reaching Denmark. According to Danish authorities, the virus was detected on the island where Copenhagen is located, while cases have also been reported in neighboring Germany, the Netherlands and France.

Denmark’s first case surfaced in early August on a farm near the German border, where both sheep and cows were infected.

In response, Danish officials quickly informed the European Commission and initiated a vaccination campaign to curb the virus’ spread. The Danish Veterinary and Food Administration also highlighted concerns about potential cases on the island of Funen in central Denmark, where tests are currently underway.

“The probability of the virus spreading via mites to the whole country is therefore considered to be high,” the administration said in a statement.

News of the cases of bluetongue in Denmark comes after a 2006 outbreak eventually spread to most of Europe by 2009. It had a major economic impact with large numbers of livestock lost. In Germany, the outbreak was estimated to have cost up to 203 million Euros ($217 million). Across Europe in total, it is believed to have cost billions, researchers said, before a mass vaccination program eventually got it under control.

However, the virus re-emerged in France in 2015. Cases were later detected in Germany, Switzerland and Belgium. How and why the virus had reappeared was unknown, but it is thought the virus had continued to circulate at low levels in wild animals.