Two horses have been euthanized and dozens more placed in quarantine in a rare outbreak of West Nile virus (WNV) in southern France.

A 3-year-old Anglo-Arab mare was euthanized after developing neurologic signs and fever, according to the French surveillance center for equine pathologies (RESPE) in Caen. The mare was the first horse to test positive in the outbreak. Of the 18 other horses at the farm in the Gard (in southeast France), two were found to be carriers of the virus, indicating recent infection. However, neither horse exhibited any clinical signs, RESPE reported.

Additionally, a 3-year-old Lusitano stallion in a farm in the nearby Bouches du Rhône also fell ill with the disease, showing signs of fever and ataxia (incoordination). His clinical signs and health progressively worsened and, after seven days, he was also euthanized, RESPE reported. On this farm, only one of the other 60 horses tested positive for WNV. That horse’s clinical signs—muscle twitching, lip trembling, refusal to move, general weakness, and hyperesthesia (hypersensitivity to touch and sound)—began nearly two weeks after the young stallion was euthanized.

A total of 20 horses at 16 different sites, all centralized in three departments along the French Riviera, have been found positive for WNV. Two of the horses tested positive for infection but showed no signs of disease