First discovered in the United States in 1955, epizootic haemorrhagic disease virus mainly affects white-tailed deer and domestic cattle. The virus has since spread to Asia, Australia and Africa, but until last year no cases had been detected in Europe. In cattle, this potentially fatal disease causes fever, anorexia, lameness and respiratory distress. Small ruminants can also carry the virus but no symptomatic cases have been detected so far. It cannot be transmitted to humans.
A consequence of climate change
The virus is transmitted by biting midges of the genus Culicoides. "Fifteen years ago, we never imagined that the disease would one day arrive in Europe," said Stéphan Zientara, director of the Virology joint research unit, which brings together scientists from ANSES, INRAE and the Alfort National Veterinary School. "Its spread is a direct consequence of climate change, which enables the midge vectors to survive in our regions."
The first cases in Europe were detected in Sardinia on 25 October 2022. A few days later, cases were reported in Sicily, followed by two outbreaks in Andalusia in mid-November. "Although it is possible that the virus was introduced through the transport of infected cattle, the most likely hypothesis is that midges were carried across the Mediterranean by the wind," the scientist continued. “This would explain the simultaneous occurrence of the disease in several places in southern Europe." The virus is identical to one detected in Tunisia in 2021.
A strain that had not been detected since 1982 in Australia
As the World Organisation for Animal Health (WOAH) reference laboratory for epizootic haemorrhagic disease, ANSES helped identify the serotype circulating in Tunisia. EHD virus has seven different serotypes. The one that was circulating in Tunisia and then arrived in Europe belongs to serotype 8. This serotype had not been detected since its appearance in Australia in 1982.
No vaccine available against this serotype. The vaccines used in Japan and the United States were developed for other serotypes and will not be effective against this one. Manufacturers are therefore considering developing a suitable vaccine against this serotype. In the meantime, the only way to curb the spread of the virus is to test animals and ban the transport of ruminants from infected areas, but this measure is still relatively ineffective.
Another threat comes from the fact that it is unknown whether European deer are susceptible to the disease. One infected deer was detected in Sardinia but it is still too early to tell whether it was an isolated case. In order to detect the arrival of the virus in France, a surveillance system has been set up with the aim of analysing any suspect animal, particularly among wildlife.