There is a new flu virus going around. It initially looked quite lethal, and caused panic. Now it is clear that it has killed relatively few victims — and many of those have underlying conditions. It is particularly dangerous to be the possessor of a pushed-in nose — that is, to be a Pekingese, a pug or a Shi-Tzu.
It is the H3N8 dog flu. The virus, scientists believe, jumped from horses to dogs at least five years ago, but it has never infected a human.
Last week, the United States Department of Agriculture announced that it had approved the first vaccine for it.
While fears of a flu pandemic among humans have shifted from the lethal H5N1 avian flu to the relatively mild H1N1 swine flu, the H3N8 canine flu has been a quiet undercurrent in the United States, rarely discussed except among veterinarians and dog owners in the few areas where it has struck hard: Florida, New York City’s northern suburbs, Philadelphia and Denver.
In line with the virologists’ adage that the only predictable thing about flu viruses is that they are unpredictable, the dog flu has baffled those following it.
“I don’t think we know what this virus is going to do yet,” said one of its discoverers, Dr. Cynda Crawford of the University of Florida veterinary school.
When Dr. Crawford began studying it in January 2004, it had come to her notice as a mysterious cough and pneumonia that killed a third of the greyhounds at a Florida dog track. By the next year, she had found it in seven states and had shown that it could be passed by dogs who just rubbed noses on the street or shared a water dish, and that humans could carry it on their clothes. There was a brief flurry of fear that it would kill 1 percent to 10 percent of the country’s 70 million dogs.
It has proved about as deadly as Dr. Crawford predicted. She estimates that by itself, it kills 5 percent of the dogs that catch it. Add the deaths at shelters that eliminate the virus by killing all their dogs and disinfecting their cages, and the total mortality rate is 8 percent.
(By contrast, the mortality rate of the 1918 Spanish flu in humans was about 2 percent.)
But it has not spread nearly as vigorously as she expected. It has now been found in 30 states, but almost exclusively in settings where dogs live closely together: shelters, pet stores, kennels and dog schools. Because the owners of these establishments have learned to turn away sick dogs just as school principals facing swine flu send home sick children, the disease’s progress has been slowed.
“Probably over 10,000 dogs have been infected,” Dr. Crawford said, “but I can’t say whether it’s 20,000 or 30,000. In a population of 70 million, that’s a drop in the bucket.”
Dr. Edward J. Dubovi of the veterinary school at Cornell University, another discoverer of the virus, said it is “probably not as well adapted to dogs as it could be.” It took five mutations to let it jump to dogs from horses, where it had circulated for 40 years.
Another mutation or two “could make it a very serious issue,” he said, but at the moment, “it takes a certain density of dogs to keep it going.”
Some veterinarians have found that the dogs that tend to die from it are the “brachycephalics” — dogs with short snub noses.
Just as obesity has proved dangerous to human flu victims because of the weight on their chests, being bred to have a short, bent respiratory tract is dangerous for dogs.
“It really puts a strain on their ability to breathe,” Dr. Crawford said. “They can’t move air in and out of their lungs.”
Do you have a question about dog flu? Dr. Cynda Crawford answers readers’ questions about canine influenza and the first vaccine approved for it.
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