When farmers in Switzerland and southern Germany noticed in June that their cows were getting sluggish, suffering from diarrhea and producing less milk than normal, many initially assumed it was an effect of the scorching heat wave gripping Europe. But as more farms fell ill — including some in eastern France — researchers began hunting for another cause.
After standard tests ruled out the likely suspects, teams from the Friedrich Loeffler Institute (FLI) in Germany and France's National Research Institute for Agriculture, Food and Environment independently found the real culprit: a virus never seen in Europe before, and one almost certainly transmitted by biting midges. The pathogen belongs to the orthobunyavirus family, the same large group that causes diseases in livestock and a few human illnesses, including Oropouche fever. It shares more than 90% of its genome with Shamonda virus, a midge-spread pathogen first isolated from cattle in Nigeria in 1965 and since found across Africa and in Japan. Because it matches no strain in international genomic databases, researchers are calling it "Shamonda-like" for now; it may eventually be classified as a variant of Shamonda.
For many scientists involved, it feels like déjà vu. The preprint the teams posted last week even opens with the words "It happened again." In 2011, some of the same FLI researchers discovered another Shamonda relative — Schmallenberg virus — causing fever, diarrhea and milk loss in German cows. It then tore through herds across Europe, triggering massive numbers of stillbirths and malformed offspring in animals infected early in pregnancy, and it has never left. "This virus is racing through herds," says Martin Beer, a veterinary virologist at FLI. "And once you get a virus like this spreading locally, you don't get rid of it again."
Switzerland's Institute of Virology and Immunology, which confirmed the finding in Swiss samples, reports that outbreaks on affected farms ran about 14 to 21 days, with fever above 40°C, a sharp drop in milk production, loss of appetite and diarrhea. The disease is not classified as highly contagious under animal disease rules, and Simbu serogroup viruses — this group — are not generally considered zoonotic, so the risk to humans is judged low for now.
Key questions remain: whether past Schmallenberg infection offers protection, which species beyond cattle can be infected, whether the virus will cause malformations and stillbirths, and where it came from. The most likely route, Beer says, is an infected midge carried on a plane — after a blood meal, heat can help viruses break out of the midge's gut and reach its salivary glands, from where they infect the next animal. Several midge-transmitted ruminant viruses have reached Europe in recent years, including new bluetongue strains and epizootic hemorrhagic disease virus. "Globalization is helping them spread and the higher temperatures may then help them establish themselves here," Beer notes.
