Canine flu is traced to 1999

Gainesville, Fla.— Canine flu has been circulating in the United States canine population since at least 1999, according to a recent University of Florida (UFL) College of Veterinary Medicine (CVM) study.

Though first identified in the canine population in 2004, antibodies to influenza A H3N8 found in dogs show it began circulating in 1999, and possibly earlier, says Tara Anderson, DVM, a graduate student and study leader.

Through a partnership with the Centers for Disease Control (CDC), Anderson and other researchers conducted a retrospective survey of serum samples collected from retired racing Greyhounds, looking for antibodies to H3N8 equine and canine influenza viruses. The samples were collected from 549 dogs that had retired from the track in 1999 through 2004 and entered a blood donor program at Hemopet/Pet Life-Line, a canine blood bank in Garden Grove, Calif.

"We are trying to identify when the influenza A H3N8 virus was first introduced into the canine population. Since canine influenza virus is most closely related to equine viruses, we believe there was an introduction of equine influenza into the canine population, but we don't know when, where or why that occurred," Anderson says. "(Canine flu) was first identified in racing Greyhounds in early 2004, and in 2004 we also started to see the virus in the pet dog population and in shelters. So we know the first time it was isolated, but we don't know when it was introduced, or how," she says.

Researchers tested the Greyhound serum samples for antibodies to a 1999 H3N8 equine influenza virus and the 2004 H3N8 canine influenza virus. The results: in 1999, 33 percent of dogs tested positive for antibodies to one or both of the influenza viruses. Thirty-eight percent followed in 2000, 19 percent in 2001, 1 percent in 2002, 40 percent in 2003 and 28 percent in 2004.

"We think it is possible that the virus was introduced before 1999, but we haven't been able to identify any archived Greyhound samples prior to 1999 for additional testing," Anderson says.

As canine influenza remains a problem, researchers continue to study the virus and the changes and adaptations it has made over time.

"Canine influenza has infected dogs in 25 states and in Washington D.C., and there are still ongoing outbreaks that occur, certainly in hot spots like Florida, Colorado and New York," Anderson says.