ITHACA, N.Y. -- A Cornell University virologist has isolateda highly contagious equine flu virus that is spreading asometimes-fatal respiratory flu among dogs, and is responsible for amajor dog-flu outbreak in New York state. There is no evidence that thevirus could infect people.
According to a paper published in theSept. 26 issue of Science Express (Vol. 309, No. 5743), the onlineversion of Science magazine, this is the first time an equine flu virushas been found to jump species.
The equine influenza virus, H3N8,was isolated at Cornell's College of Veterinary Medicine afterUniversity of Florida researchers sent fluid and tissue samples fromgreyhound race dogs that had died from a respiratory illness at aFlorida racetrack in January 2004.
"Of all animals, dogs have themost intimate contact with humans on a daily basis, so the potentialfor human infection has to be in the back of our minds," said EdDubovi, director of the virology center at Cornell's Animal HealthDiagnostic Laboratory, who isolated the virus from the University ofFlorida samples.
Still, he added, there is no evidence of thevirus jumping to humans, and there is no expectation of it doing so. Itis possible the equine virus has been infecting dogs for some time,although the symptoms are very similar and could be mistaken for common"kennel cough," a bacterial disease related to pertussis (whoopingcough) in children. Nevertheless, the paper cautions that the newlydiscovered flu virus must be closely monitored.
With close to 100percent of dogs exposed to the virus becoming infected and about 80percent of infected dogs showing symptoms, the flu could be spreadingthroughout the country. It was originally documented in greyhounds attracks and kennels but now is infecting all breeds of dogs. Ongoingtesting is being done to track the spread of the virus to differentregions of the country.
"Right now, we have a major outbreak ofthis disease in all breeds of dogs in New York state," said Dubovi,noting that symptoms can include high fever and a respiratory infectionthat lasts a few weeks, although 1 to 5 percent die from relatedhemorrhagic pneumonia. From January to May 2005, outbreaks occurred at20 racetracks in 10 states (Florida, Texas, Arkansas, Arizona, WestVirginia, Kansas, Iowa, Colorado, Rhode Island and Massachusetts),according to the paper.
"This infection will become a majorconcern for all dog owners, since 100 percent of dogs are susceptibleto infection by this virus ," said Dubovi. "With 50 million pet dogs inthis country, even if you have 1 percent mortality, this is going toresult in a number of dogs dying from it."
The Centers forDisease Control and Prevention (CDC) in Atlanta sequenced the virus'entire genome and found all the segments were from the equine virus.This is unusual, because flu viruses will often swap genetic materialwith other flu viruses when they jump species. For a new virus to enteranother species it must overcome a number of barriers, such as findinga cell receptor to bind to in order to enter the cell and to reproducesufficiently in the new host.
"There are probably many examplesof viruses jumping species, but then it becomes a dead-end issue," saidDubovi. Researchers have long known that equine flu was capable ofgrowing in dogs, since scientists experimenting with equine influenzause cell lines from canine kidney cells.
When Dubovi firstreceived the University of Florida samples, he and his colleaguesisolated a virus and determined that it was an influenza not typicallyfound in dogs. The next step was to test to see if it was an avian fluvirus, like the virulent H5N1 that has jumped from birds to humans overthe last few years. A highly sensitive test -- called a PCR (polymerasechain reaction) that amplifies and detects small amounts of DNA or RNAin a blood or tissue sample -- ruled out avian flu strains H5 and H7.
Theisolate was then sent to the CDC where Ruben Donis, Cornell Ph.D. '87,one of Dubovi's former graduate students and currently chief ofmolecular genetics for the influenza branch, found that it testedpositive for equine influenza virus. Donis also ruled out thepossibility that the sample had been contaminated with equine virusfrom another source.
The study by lead author, Cynda Crawford, animmunologist at the University of Florida's College of VeterinaryMedicine, was funded by the State of Florida's Division of ParimutuelWagering in response to ongoing respiratory problems in racinggreyhounds.
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