Heartworm risk tiny, experts say
State veterinary experts say heartworm in dogs and cats is rare in Washington, and there doesn’t appear to be an outbreak here.
The Washington State Veterinary Medical Association wants to alleviate pet owners’ concerns after receiving several dozen phone calls following a July 1 Spokesman-Review article that reported that heartworm, a parasite that can kill dogs and cats, may have found its way to the Inland Northwest.
They’re not questioning the fact that three animals treated at a Liberty Lake animal clinic tested positive for heartworm.
“People frequently see a report about diseases advancing or parasites advancing and often react or overreact,” said Charlie Powell, public information director for the association.
“They need to keep it in perspective. It certainly doesn’t mean that you’re on the verge of becoming an area that has the disease all the time, every year.”
Heartworm may occur in cats and dogs – including coyotes and wolves – and some other animals. It is spread when mosquitoes feed on an infected animal, ingest the baby worms from that animal’s bloodstream, and then feed on other dogs or cats. Adult worms settle in the right side of the heart, causing heart failure.
Mark Fosberg, a veterinarian at Animal Clinic at Liberty Lake, recently sent a letter to area veterinarians alerting them that two cats and a dog treated at his clinic tested positive for heartworm, which is rare in this area.
“All I know is that I have three positive tests. It’s a little more complicated with the cats, but at the very least, it indicates heartworm exposure, and the dog definitely tested positive,” said Marni Quist, another veterinarian at the Liberty Lake clinic.
Quist said that the dog and cats have never been out of the Liberty Lake area. They felt it was prudent to let other veterinarians know what they found.
“Veterinarians are taught to look for clusters of cases, and when clusters of cases of a disease that are not normal in an area occur, they realize that we could be – and I emphasize ‘could be’ – on the verge of seeing more of the disease. But they also realize that may not be the case,” Powell said.
Bob Lobingier, veterinary pathologist at ANTECH Diagnostics in Portland, where the Liberty Lake clinic’s tests were processed, said the heartworm antigen test is 99 percent accurate and is the best available screening test for heartworm infection in dogs.
Lobingier also said there is no indication of an increase in confirmed heartworm cases in the region.
“We do somewhere between 2,000 to 3,000 heartworm tests a year in the Pacific Northwest, and we probably get between 20 and 25 positives. Of those, the great majority are infected outside the area. Occasionally, rarely, we see a dog that tests positive that appears to have never left the area,” Lobingier said.
The cats’ diagnosis is more difficult. Lobingier said a heartworm antigen test wasn’t used with the two cats tested from Liberty Lake. Cats can be screened with heartworm antibody tests, but those tests only indicate exposure, not infection.
“Cats more rarely get heartworm, and the probability for infection is very low, especially in areas where heartworm does not exist or is very rare, like what has been the experience in Washington,” Powell said.
According to a 2004 Gallup Poll, more than 250,000 cases of heartworm disease were reported in the United States with most cases in Texas, Florida, North Carolina, Georgia and Louisiana.
“It’s difficult to transmit heartworm in the Northwest,” Lobingier said. “We have the right mosquitoes, but we don’t have a large mosquito population and we don’t have the right climate to help that along. Heartworm presence in the Northwest isn’t zero, but very close to zero. I’ve seen nothing that indicates a heartworm outbreak.”
Powell said pet owners should discuss their pets’ care with their veterinarians, who can make recommendations about testing and preventative care based on individual circumstances.