Sunday, February 26, 2006

Fido can get sick, too

What is it about the flu these days?

First it crosses from birds to humans, creating a panic that it will develop the ability to transmit person-to-person too.

Now, it has crossed species barriers again, this time from horses to dogs. Man’s best friend is at risk, and given how close we are to our dogs, we could be at risk again too.

This “dog flu” was first identified in racing greyhounds in Florida in 2004 and was found to closely resemble a horse flu strain. Although the virus initially infected dogs directly from horses, at some unknown point it developed the ability to transmit from dog-to-dog too, probably by modifying its genetic information slightly.

“The significance is that historically, the transmission of an influenza virus from one mammal to another is a rare event,” says Cynda Crawford, a veterinary immunologist from the University of Florida’s College of Veterinary Medicine and the lead researcher in the study. This is also the first evidence of a flu virus ever spreading between dogs, she says: “We don’t have much precedence for this.”

Since dogs are kept in close contact with people – and are so very generous with their saliva – dog flu strains could start infecting people and eventually develop the ability to transmit person-to-person, as is feared could occur with current strains of bird flu.

Animal flu strains are more dangerous to people than human strains because people’s immune systems are not used to fighting them, so if such a virus acquires the ability to transmit between people, it could potentially lead to a pandemic. The flu pandemics of 1957 and 1968, which are believed to have killed over 100,000 Americans, were bird flu strains that had acquired the ability to infect people and transmit easily between them. If the dog flu also evolved in this way, it could potentially cause a pandemic too.

Edward J. Dubovi, Director of virology at the Cornell University College of Veterinary Medicine, who first isolated the dog flu, says that the potential for a second species jump from dogs to humans is “a low probability event,” but adds that, since dogs and humans are so frequently in close contact, dogs would be “the perfect species” from which to jump.

However, Ruben Donis, Chief of the molecular genetics section at the Influenza Branch of the Centers for Disease Control and a collaborator in the study, explains that the horse flu has existed for at least 40 years and that there is no evidence that it has ever infected a person, via dogs or otherwise. While the virus has changed slightly since it began infecting dogs, the modifications have been small and are unlikely to significantly increase the risk for humans.

“We are going to monitor all cases of possible human exposure, but at this point, there is no reason to panic,” Donis said in a CDC Media Telebrief in September.

Over the course of the past few months, over 3,000 samples from potentially infected dogs around the country have been sent to Dubovi and other Cornell University scientists. However, all but five or six of the samples have been difficult to fully analyze because they were taken from dogs in late stages of infection.

“The samples we are getting are not appropriate for what we’re after,” he says.

Because of this, it has been difficult to determine how the virus has been changing as it spreads – information that is very important to ensure that it does not become more virulent or pose a danger to people. Dubovi explains that it will be crucial in the coming months to maintain surveillance and get better samples.

Analysis has, however, revealed that dogs in 18 states, including New York, have had the flu, says Crawford. And virtually all exposed dogs have become infected, according to the American Veterinary Medical Association website.

While no one knows how many dogs have been killed, only about one in every 20 infected dogs dies, and household pets have fewer complications than dogs in shelters, says Crawford. A number of infected dogs never experience any symptoms, although they can still make other dogs sick.

Crawford advises that there is no need for people to panic – they should still feel comfortable taking their dogs to parks and dog runs and allowing them to participate in community activities with other dogs.

Scientists have also been developing a dog flu vaccine, and Crawford estimates that it will be available by this summer. The vaccine should limit transmission and greatly reduce the risk posed to people.

If your dog is coughing or seems to be suffering from a respiratory infection, it is important to have it checked immediately by a veterinarian, says Dubovi, who explains that post-flu complications like bacterial infections are usually more dangerous than the flu itself.

“The critical thing is for the dogs to be treated quickly once they develop clinical signs,” he says.


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