France has detected the Shamonda virus, which usually affects livestock, in a human for the first time in a patient who died early October.
French health authorities said that until now the virus was considered non-transmissible to humans.
Shamonda virus is an insect-borne Orthobunyavirus primarily affecting livestock, particularly cattle, and transmitted by biting midges.
First identified in Nigeria in the mid-1960s, it has since been detected sporadically in animals in Africa and Japan.
It has been spreading among several European countries this year.
France's weekly animal health surveillance bulletin said the virus had also been detected in Austria, Belgium, Ireland, Italy, Liechtenstein, Luxembourg, the Netherlands, Portugal, Slovenia, Spain, and the UK's Jersey.
The European Centre for Disease Prevention and Control (ECDC) said it was investigating how the virus had spread to a human.
The French authorities said the patient was being treated for a serious illness in a Lyon hospital and experienced neurological complications thought to be linked to the virus.
The leading hypothesis is that the patient may have been infected in eastern France, where the virus had been circulating among animals during spring and summer 2026.
Cattle are considered its main animal hosts, although sporadic infections in smaller livestock and horses have also been identified in France this summer.
The virus has several effects on animals, including fall in milk production, diarrhoea, weakness, loss of appetite and fever.
Unlikely to spread: WHO
The World Health Organization said on Thursday (22) it was unlikely that the first documented human case of the Shamonda virus disease would spread further, adding that it was monitoring the situation.
"Based on current information and knowledge of the transmission of closely related viruses, this is an isolated human case and it is unlikely to lead to wider spread at this time," the WHO told Reuters in a statement.
It is suspected that the victim was bitten by a midge carrying the virus.
