As flu season begins and doctors promote flu shots and await patients coming in with the familiar symptoms, veterinarians are anticipating visits from their own patients.
Although their viruses rarely spread to humans, a variety of animals suffer from their own strains of influenza.
"Several animal species are susceptible to influenza or flu viruses -- birds, ferrets, pigs, marine mammals and horses," said Kathy Connell, a veterinarian with Foxglove Consulting in Olympia, Wash.
Although there have only been a small number of canine cases, dogs were added in the last few years to the list of animals that have contracted influenza.
Bird flu has garnered the most attention in recent years because of its transmission to humans in Asia. While many have feared that avian influenza could become the next pandemic, it has not yet mutated into a form that can spread from human to human.
However, progress has been slow on creating a vaccine for it. One problem has been that current vaccines are grown in fertilized chicken eggs, and as Columbia University epidemiologist Stephen Morse noted in an interview with ABC News last month, "A virus that is lethal to chickens is very hard to grow in eggs."
But despite the fears, an avian flu pandemic has not arisen, and the virus has been monitored by the World Health Organization for more than a decade.
At present, perhaps the most widespread vaccination for flu in animals has been done for horses.
Equine influenza, while it cannot spread to humans, can be devastating to a herd of horses, as almost all horses that are exposed to it become infected. The American Veterinary Medical Association estimates that up to 90 percent of horses in a herd that has not previously been exposed to the virus can die.
Horse flu has been a problem almost everywhere in the world. As of November 2006, the medical association had noted that only Iceland, New Zealand and Australia were "considered to be free of the virus."
But that changed in 2007, when equine influenza hit Australia.
Influenza Danger to Livestock"Australia's prior freedom from influenza made the recent incursion especially devastating, but our own industry in the United States also suffers," said James Maclachlan, a professor of microbiology and immunology at the University of California at Davis School of Veterinary Medicine.
A primary problem for industry, whose value is placed at $100 billion and includes racing, showing and recreational use of horses, according to Maclachlan, is that so-called shuttle stallions -- breeding males who go between the United States and Australia and New Zealand at the varying mating seasons -- are kept out over fears of infection.
A primary problem is that so-called shuttle stallions -- breeding males who go between the United States and Australia and New Zealand at the varying mating seasons -- are kept out because of fears of infection.
The economic impact is felt in the horse racing industry, as equine flu forces the cancellation of races.
The outbreak in Australia had both its own populace and that of nearby New Zealand worried.
After an investigation in New Zealand in April that revealed test results were contaminated and incorrectly showed that equine influenza had reached the island nation's shores, the New Zealand Herald wrote, "The test results were crucial because an equine influenza outbreak would put at risk New Zealand's place as the only significant horse-racing nation free of equine flu."
Bark of Some Flus Worse Than Bite
Equine influenza may have reached even further a few years back, when it is believed to have spawned canine influenza. The first documented cases of dog flu, according to the medical association, occurred in racing greyhounds in Florida in January of 2004.
But fears of widespread infection to family pets were never realized.
"When that outbreak went out into the general population ... actually it was very rare for us to see dogs get very ill with influenza," said Sarah Sheafor, medical director of SouthPaws Veterinary Specialists and Emergency Center in Fairfax, Va.
While her clinic treats a number of dogs with cancer, Sheafor notes that even the canines with weakened immune systems didn't come down with the virus.
"Everyone was worried just because it was a new influenza and we had never really seen influenza in dogs before," she said. "Since that summer, I would have to say we've seen fewer than three or four where we even worried about it."
Spread of Disease: Fear of Virus from Animal and Human"There was a lot more worry and a lot more flash in the pan than it needed," Sheafor said.
The same could be said for swine flu, which affects pigs.
As Dr. Jeffrey Greene, a professor of clinical medicine at NYU, notes in his book "The Bird Flu Pandemic: Can It Happen? Will It Happen?" a widespread panic occurred in 1976 when a soldier at Fort Dix, N.J., died of the disease. Overall five recruits were infected.
Ultimately, Greene noted, 40 million people were vaccinated against a pandemic that never came about.
But the medical association notes that pigs present a unique opportunity for flu viruses. Avian, swine and even human influenza can bind to the cell receptors in a pig, which allows the strains to mix together and form new viruses.
While pigs and birds may have passed their infections to humans, for ferrets the transfer goes in the other direction. They can contract human flu.
"Ferrets can get a few different respiratory elements from other species," Sheafor said.
Unlike other pet owners, ferret owners may need to take extra precautions when they are sick.
"People with flu who might be shedding the influenza virus should wear gloves and face masks when handling ferrets. There is no protective vaccine available for ferrets," Connell said.
While stories of animal flus come up from time to time, few of the strains are a hazard to humans, and some haven't even presented a major risk to the animals.
"It's not a disease that we worry about a great deal in dogs," Sheafor said, explaining that while a kennel with many dogs packed in might pose a problem, the home environment doesn't tend to do so.
"Dogs with the flu sure look a lot like people," she said, "but we didn't see a big epidemic."