Pets in mosquito-prone areas need protection from heartworm

On an X-ray, if your dog’s heart looks as if it’s clogged with cooked spaghetti, the diagnosis is likely to be heartworm. Heartworm is transmitted by mosquitoes and can be prevented by a prescription pill.

his image courtesy of Henry Moore Jr. BCU/WSU shows heartworm in a dog heart preserved in formalin at Washington State University. The heart was lit from the bottom to show the surface texture of the heart and to outline the heartworm.

his image courtesy of Henry Moore Jr. BCU/WSU shows heartworm in a dog heart preserved in formalin at Washington State University. The heart was lit from the bottom to show the surface texture of the heart and to outline the heartworm.

On an X-ray, if your dog’s heart looks as if it’s clogged with cooked spaghetti, the diagnosis is likely to be heartworm.

Heartworm is transmitted by mosquitoes and can be prevented by a prescription pill.

It’s endemic warm regions and veterinarians agree that pet owners in this region must give their animals preventive medicine year-round or face a strong risk that their pets will contract a disease that’s fatal if untreated.

But there is debate over whether heartworm prevention treatment is necessary everywhere, and whether prevention is necessary year-round.

Heartworm is also present in Canada and it is on the increase.

A 2010 study published by the Ontario Veterinary College’s Department of Pathobiology at the University of Guelph shows a 60 per cent increase in the number of pets in Ontario carrying the potentially fatal heartworm parasite.

The 2010 report showed that 564 dogs tested positive for heartworm in Canada in 2010. Of those dogs, 431 were located in Ontario, a significant increase in cases compared to the last study conducted in 2002, when there were 268 reported cases in the province.

Also of concern is that 80 per cent of the dogs that were diagnosed with heartworm had not been on heartworm preventive medication.

Dr. Ted Kilpatrick, president of the Ontario Veterinary Medical Association, said in a release Tuesday that he believes the results of this study support the importance of preventive veterinary treatments.

Dr. Shelly Rubin of Chicago, a retired veterinarian and past president of the American Heartworm Society, advocates treatment for every dog, every cat, everywhere, every month. The Society, founded in 1974, is sponsored by manufacturers of heartworm pills but run by veterinarians.

On the other side of the debate, Dr. Marty Goldstein, a holistic veterinarian from South Salem, N.Y., said the treatment should be used as sparingly as possible depending on your location.

He believes toxicity from preventive drugs and even some vaccines are causing immune systems to fail in animals trying to fight threats like liver disease and cancer.

Goldstein said he might see three heartworm cases a year, but he is seeing five to 10 new cases of cancer a week at his Smith Ridge Veterinary Center.

Dr. Mark D. Kittleson, a veterinarian and professor in the Department of Medicine and Epidemiology at the University of California, Davis School of Veterinary Medicine, doesn’t give his dog Max a preventive because heartworm in Davis is so rare. But if Max travelled even 100 km east to Grass Valley, Kittleson would want the dog to have the pill, Kittleson said.

Pets in areas where heartworm is endemic not only need preventive medicine, but they should also be tested annually to make sure they don’t have the disease, Kittleson said. The test is done using a blood sample.

Mosquitoes pick up heartworm larvae when they bite infected dogs. The mosquitoes then retransmit the larvae to other dogs. Eventually the worms get into the animal’s blood vessels and lungs, where they can grow 25 to 30 centimetres long.

The infection takes six months to develop, and during that time there are few clinical symptoms beyond a cough, Kittleson said.

Most treatments involve arsenic-based drugs that slowly kill the worms, Kittleson said. Treatment involves three painful injections and six weeks of confinement for the pet, he said. Seventy to 80 per cent of dogs that undergo the treatment survive, Kittleson said. Treatment can cost $1,000.

The preventive pills work for cats as well as for dogs, but the arsenic treatment is toxic to cats. Some cats work the worms out of their systems.

People rarely get heartworm. If a worm does try to develop in human lungs, it’s likely to do little more than leave a scar, Kittleson said.

Because mosquitoes carry many diseases besides heartworm (West Nile virus, for example, which is harmful to humans), abatement programs are priorities in many regions. Homeowners can help by eliminating standing water and adding mosquito-eating fish to ponds.

William Foreyt, a professor of parasitology for 35 years at Washington State University, conducted a heartworm study from 2005 to 2007, looking at 556 coyote hearts from animals trapped in central and eastern Washington.

“None of those coyotes was infected,” Foreyt said.

He does not give his dogs preventive medicine.

On the other hand, he noted, Washington state received two shipments of Katrina animals and 50 per cent of them were infected with heartworm.

But even if you live in a place where heartworm is uncommon, your dog may encounter the disease elsewhere. For that reason, Foreyt recommends pet owners give preventive medicine if they’re vacationing with pets in heavy mosquito country.

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