Regional spikes in parvo cases don't signal a national trend, virologist says

NATIONAL REPORT — Parvovirus cases have spiked in some parts of the country, with veterinarians in New York and Arizona reporting increases of 75 percent and 330 percent, respectively.

Dr. Andrew Newmark, chief veterinarian at Lollypop Farm, the Humane Society of Greater Rochester, N.Y., says his shelter is seeing about 25 more cases than this time last year.

"This is probably the most I remember, and I've been here 12 years," he says.

In Arizona, Dr. Lorakate Snyder, an associate veterinarian at Chocise Animal Hospital in Bisbee says cases have gone from about three a week to 10 a week over the last month or so.

But parvovirus expert and internationally known virologist Dr. Ronald Schultz, professor and chair of the Department of Pathobiological Sciences at the University of Wisconsin-Madison School of Veterinary Medicine says a nationwide increase in cases is not happening.

"That's more perception than reality," Schultz says. "They're very much in pockets."

But some veterinarians believe a combination of factors—including the economic recession, weather conditions and vaccine frequency—is causing parvo cases to rise in parts of the country.

"I've heard some banter on our Association of Shelter Veterinarians list serve reporting they think they are seeing more cases this year," says Dr. Cynda Crawford, clinical assistant professor in the Department of Small Animal Clinical Sciences and the Maddie's Shelter Medicine Program at the University of Florida College of Veterinary Medicine. However, parvo is not a reportable disease, and there is no national tracking of cases, she says.

Newmark says several practices in his area of New York have reported seeing a spike in cases, too. While always a risk in shelters, he says the increase of 25 or so more cases over last year is unusual.

"It's just shocking how many more cases there are this year than we usually see. We're an open-admissions shelter, so we can get anybody," he says. "But 25 cases, for us, in this span, is certainly eye-opening."

Weather could have something to do with it, along with the economy, Newmark suggests.

"When the economy is bad, people don't take dogs and puppies to get vaccinated as (frequently) as they should," he says.

Curiously, while he normally sees Rottweiler and pit bull puppies with parvo, this spike does not discriminate by breed or age.

"This is the first year we're seeing more adult dogs with parvo," he says. "And we're seeing it in all kinds of breeds we don't usually see."

In Arizona, the virus is targeting younger dogs, but is more virulent than in the past, Snyder says.

"I'm losing a lot more than I'm saving, which is very unusual," she says. "We've been hearing that someone in the area may be giving people the recommendation to start vaccinating at 6 months of age."

So client education could factor into the pockets where parvo is spiking, too. But overall, Crawford says she believes veterinarians are doing a good job of talking to clients about the importance of vaccination. She does, however, agree that the economy may be playing a role in the increased cases.

"I think, overall, veterinarians do a good job of educating pet owners about the importance of vaccinating against parvo. So I don't know if it's a lack of education. I suspect not," Crawford says. "But it also could be, as the veterinarian in New York states, a reflection of the economic recession and the fact that owners are not choosing to spend their disposable income on following through with (their) veterinarian's recommendations on vaccinations."

Even in the veterinary community, though, there is debate about parvo vaccination protocols, Crawford says.

"There are dissenting opinions and practitioners who believe that relaxing the recommendation from every year to every three years will lead to breakthroughs in population immunity. Should we go back to vaccinating dogs every year?" she asks. "There certainly is a lot of evidence that the immunity induced by proper vaccination does last many years, even to the point that several vaccine manufacturers have demonstrated through clinical trials that dogs retain immunity and have even put labels on their parvo vaccines stating that it could be administered every three years.

"There's a lot of evidence on one hand to support every three years, but a lot of opinions on the other side saying it could lead to trouble," she adds.

Weather may be affecting the number of cases, Schultz says, since a very wet spring or fall can cause cases to spike. The virus remains viable in soil for at least a year—or up to three. As the ground dries, the virus isn't readily available, but once the rain comes, the virus can be reactive and pose a threat to any unvaccinated dogs. Adult dogs that have never been vaccinated may not show clinical signs of the disease after infection, but will shed a large amount of the virus, he adds.

Schultz says a properly vaccinated dog will have immunity to the virus for life. Involved in the isolation of canine parvovirus 2A in 1978, Schultz says he has kept close watch on the newer strains (2B in the 1980s and 2C in 2005-06) and has found all the current vaccines provide the same protection against all three.

There is an exception for non-responders, which Schultz says are one in 1,000 dogs. When the virus first emerged, 50 - 75 percent of puppies in litters from Rottweilers and Dobermans were non-responders due to a genetic trait. But today, the idea that some breeds are more susceptible to infection than others is "an old wives' tale," he says. He has seen some outbreaks that affected some breeds more than others, but typically that has been because they were breeds used for dog fighting or similar uses and had never seen a veterinarian or been vaccinated.

"Because parvo was so prevalent in the late 1970s, today we don't have any more Rottweilers or Dobermans that are non-responders. The genetics were wiped out through Mother Nature, killing them all," he says. But for the random non-responders in the general population, the virus can be deadly.

"Those dogs that are non-responders, no matter what you do, you can't keep them alive," Schultz says. "They will die."

But any dog that survives infection or is properly vaccinated develops a life-long immunity to the virus, he says.

"What we're seeing right now, because of the economy, is more and more abuse of vaccines in vaccination clinics ... overuse of vaccines," he says. "When you have a vaccine that can provide a lifetime of immunity, what we recommend in our guidelines ... is that after you complete the puppy series at 14 to 16 weeks, revaccinate at a year and then not any more often than three or more years. And lots of veterinarians are still vaccinating annually."

Animals vaccinated too often can run the risk of developing adverse reactions, such as auto-immune disorders and hypersensitivity reactions, Schultz warns.

"Vaccines are, in general, fairly safe," he says. "But they are something you don't want to use if you don't need to."

A better solution to vaccinating annually would be to figure out a way to make sure all dogs get the vaccine at least once in their lifetime, he says.

"All they would have to do is get one dose at 16 weeks of age or older and it would make such a difference for the entire population of dogs, because you would have herd immunity," Schultz says. "We can really go a long way by getting more of the unvaccinated animals vaccinated at least once. But we can't figure out a way to get all those animals vaccinated.

"There's not a veterinary practice in the United States that would allow a dog or puppy to come in and not get core vaccines," Schultz says. "If the animal ever gets to see a veterinarian, they're going to have the core vaccines."