Glanders, a fatal infectious disease, has been detected in a horse previously stabled at the 2016 Olympic equestrian facilities in Rio de Janeiro, Brazil. However, officials say the diagnosis isn’t necessarily cause for concern.

At least one horse housed at the Deodoro National Cavalry Complex tested positive for glanders via a blood serum sample in April, the Brazilian Ministry of Agriculture (MAPA) stated. The horse, belonging to the Brazilian military, was immediately euthanized.

However, the horse could have had a false positive result, said Bernard Vallat, DVM, director general of the World Organization for Animal Health (OIE) in Paris, France. Blood testing for glanders can result in false positives, and more advanced diagnostic testing must be carried out in order to have a reliable result, he said.

The Olympic venue housed military horses until less than five months ago, when the animals were removed under the request of the OIE and the Fédération Equestre Internationale (FEI), Vallat said. “We had been urging them to get the horses out of there (in preparation for the Olympic Games) … and they finally moved them out in April,” he told The Horse