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Virus Infecting Dogs Hardier Than Thought

Owners urged to get pets vaccinated against parvo

TUESDAY, Dec. 28, 2004 (HealthDayNews) -- Canine parvovirus, an organism that can sicken and kill dogs, has undergone epidemic-like growth since its appearance more than 25 years ago and is capable of doubling its population size every few years.

That's the conclusion of a new study on the virus, which experts hope will motivate people to get their dogs -- especially puppies, which are often given as Christmas presents and are especially vulnerable -- vaccinated against the pathogen.

Parvo, as it's often called by veterinarians, was first identified in dogs in 1978 and has since become ubiquitous worldwide. Even with treatment, it can prove fatal.

The rapid growth of parvo was associated with a lineage of the virus that acquired a broad range of hosts and picked up infectivity. "We're trying to understand how the canine virus emerged," said Colin Parrish, a professor of virology at Cornell University's College of Veterinary Medicine and co-author of the study, which appears in this week's issue of the Proceedings of the National Academies of Sciences.

It's an example of a virus that jumped species after first infecting cats, he said. "Parvo was first seen [in dogs] in 1978, and that is when it went around the world," Parrish said. "It went around the world pretty fast, in about two or three months.

"We think it took about a dozen changes [or mutations] to change the cat virus into a dog virus," he continued. "We think it happened over a short period of time, and in two or three stages. The virus is well-established in dogs, and it is never going to go away."

Edwin Hahn, associate dean for research at the School of Veterinary Medicine at the University of Illinois at Champaign-Urbana, said the study is noteworthy because it finds that the rate of evolutionary change in parvo is quicker than what experts might speculate for the type of virus that it is.

Parvo is a DNA virus, he explained. "People thought RNA viruses are rapidly evolving, but that DNA viruses are slower," he said. "That's the dogma." But the research on parvo and its rapid evolution and mutation proves that dogma incorrect, Hahn said.

The behavior of parvo, Parrish and his co-authors said, is closer to that of RNA viruses. Parrish said it is likely that canine parvovirus will keep improving its capacity to spread among dog hosts.

The message carries extra weight during the holiday season, when many families get puppies for holiday presents. (This is a practice many animal-care experts frown upon, in part because the present is a surprise and the recipient is often unwilling or unable to make a commitment to a new pet.) Parrish and Hahn agreed that owners not slack off on pet vaccination.

"It's a virus capable of changing rapidly, and it's very important to get the proper vaccination for your animals, because these viruses are still with us," Hahn said.

Puppies are especially susceptible to parvo, Parrish said, adding that the peak infection period often occurs between the ages 2 and 4 months. Symptoms include lethargy and diarrhea. It can be fatal.

Parrish recommends that pet owners vaccinate puppies with the parvovirus immunization at age 2 months, 3 months, and again at 4 months, and then annually.

More information

To learn more about canine parvovirus, visit the American Veterinary Medical Association .

SOURCES: Edwin Hahn, Ph.D., associate dean of research, College of Veterinary Medicine, University of Illinois at Urbana-Champaign, Urbana, Ill.; Colin Parrish, Ph.D., professor of virology, College of Veterinary Medicine, Cornell University, Ithaca, N.Y.; Dec. 27-31, 2004, Proceedings of the National Academies of Sciences
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