Equine Influenza Virus Jumps to Dogs in Florida

The first known case of equine influenza virus in dogs was identified in Florida when 80 racing greyhounds in Jacksonville were diagnosed with the virus or antibodies to the virus in January 2004. It is the first time that the equine virus has infected a mammalian species other than the horse, according to research by veterinarians at the University of Florida and Cornell University who are investigating the cause and spread of the disease with the Centers for Disease Control. The “species jumping” incident, as it has been called, may be attributed to a change in the hemagglutination protein, said Cynda Crawford, DVM, PhD, assistant scientist for the University of Florida, College of Veterinary Medicine, who is researching the outbreak.

In January, 22 of 80 greyhounds from a Florida racing kennel presented with symptoms of kennel cough. Eight of the dogs died from hemorrhagic pneumonia, and six weeks after initial testing, nearly all of the surviving dogs at the kennel – even those that initially showed no signs of disease – had developed antibodies to the virus, Crawford said.

Researchers caution that the canine variant of equine influenza occuring in greyhounds at the Florida kennel may be an isolated incident, but Crawford advises  general practitioners to watch for dogs that present with a chronic cough, fever and signs of pneumonia. She recommends a chest radiograph, chemistry panel and possibly tracheal washes for bacterial and viral culture.

At this time, there are no recommendations for prevention of exposure since researchers do not know either the source of the virus, how it is transmitted to dogs or how prevalent it is in some communities. Two vaccines are available to prevent equine influenza in horses, but Crawford strongly discourages their use in dogs. These vaccines are tested and licensed for use in horses, only, so the safety and efficacy in dogs is unknown.  “I would not use those vaccines on my own greyhounds at this time,” she said.

Although the January outbreak was the first incident of equine influenza jumping species from horses to dogs, some researchers suspect that the virus may have made the leap earlier. National outbreaks of kennel cough in greyhounds occurred in 1992, 1999 and 2003, and during those years a large percentage of greyhounds presented with kennel cough symptoms but died of hemorrhagic pneumonia, which is “totally uncharacteristic of kennel cough,” Crawford said.

Researchers are studying samples from the greyhounds that died during 1999 and 2003 to determine whether they died of equine influenza. Necropsies on five of the eight dogs that died in 2004 showed pathologic similarities to the greyhounds that died during 1999 and 2003, according to the researchers. “We are looking at the fact that this could’ve started years ago,” Crawford added.

"I think kennel cough is a misnomer because the term classically refers to a defined syndrome caused by Bordetella bacteria and/or parainfluenza virus," said Crawford. "We are still trying to determine causes for respiratory disease outbreaks in racing greyhounds."

For more information about the canine variant of the equine influenza virus, email the University of Florida.