Equine infectious anemia (EIA), a deadly equine virus carried by horseflies and mosquitoes, has forced veterinarians to destroy more than 120 horses in Alberta, Canada, this year, a federal agency says.

An incurable disease, EIA is commonly known as swamp fever. The disease is caused by a virus which infects red blood cells in horses, donkeys, and mules. When the animal’s immune system destroys the infected blood cells, its reduced blood count causes anemia.

“They begin losing fluids, their legs swell up, and they get sick, lethargic and weak… You catch it, you die. It’s kind of a dreaded disease,” said Ardrossan veterinarian and equine specialist Bob Jones.

Doug Scott, a veterinarian with the Canadian Food Inspection Agency, said about 125 horses have been diagnosed with swamp fever in Alberta in 1999. “To my knowledge, they have all been destroyed,” he said. Although Scott could not say how many Alberta horses died due to the virus last year, the Saskatchewan Horse Federation said 63 infected horses were found in 1992 across Canada