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Keeping Pets Safe From Heartworm

By Brian J. Lowney
Contributing Writer

June 14, 2012

Veterinarians are urging owners to have their cats and dogs checked for heartworm and to take precautions to prevent the disease from infecting the family pet.

Many different species of mosquitoes transmit heartworm, and over the years the disease has become a more prevalent problem in northern latitudes. Mosquitoes are starting to emerge as a result of the unusually warm spring and recent warm weather, so small animal practitioners advise pet owners — even those who own indoor cats — to take the necessary steps to safeguard their four-footed companions against heartworm or to treat the disease in the aftermath of infection.

According to veterinarian Nandini Jayaram, of Capeway Veterinary Hospital in Fairhaven, the parasite or "worm" carried by the mosquito migrates through the tissues of the animal's body, and then settles in the blood vessels of the lungs and the right side of the heart.

"Heartworm is a very preventable disease," says Dr. Thomas Burns, hospital director at Veterinary Associates of Cape Cod in South Yarmouth.

"Obviously, it is much better for a dog never to get heartworm; the damage to the heart, lungs and other organs such as the liver can be permanent."

Burns says it's important that dogs and cats be placed on a regimen of preventative medication. While dogs have been traditionally treated with a monthly pill, the Burns says that all too often the treatment plan becomes ineffective when owners forget to administer the medication.

One alternative is an injection that lasts six months and costs about the same as the monthly oral medication. Burns says that there are also reminder emails sent by the veterinary clinics and mobile apps that help owners remember to give the medication.

Jayaram says that heartworm disease usually occurs when there has been a gap in prevention, such as when an owner skips treatment during the winter months because he thinks it's too cold for mosquitoes.

Burns says that while there is no heartworm treatment for cats, it's important that felines — especially those allowed outdoors — also receive preventative medication. Cats can be treated with a monthly topical application instead of a pill — something that most fussy felines and their owners appreciate.

Burns says that many cases of heartworm are diagnosed during routine blood tests, which often also screen dogs for diseases transmitted by ticks, such as Lyme disease. Cats, he adds, are rarely screened for these illnesses.

"Testing is critical because it allows us to find the heartworm before it becomes advanced, allowing us to treat the animal while it is still healthy and giving the patient a much better prognosis," Burns says, adding that it can take several years before heartworm is clinically noticeable.

Unfortunately, by the time an owner notices signs of the disease, it is often already in an advanced and critical stage and the canine is very sick.

Dogs with advanced heartworm display symptoms such as coughing, shortness of breath and fatigue. If the disease is not promptly treated, it can cause organ failure and death.

"Severely infected dogs can die suddenly during exercise or exertion," Burns says.

While heartworm disease is much more common in dogs than cats, he says, the disease rate in felines is much higher than most experts recognize.

"Clinical signs of heartworm in cats are often much more subtle, or misinterpreted as other conditions such as asthma or heart failure," Burns says, adding that the disease is much more difficult to diagnose in felines, partly because the testing is more extensive and less reliable. One study, he says, found that upwards of 15 percent of indoor cats have been exposed to heartworm disease in certain regions.

According to Jayaram, signs of advanced heartworm disease include coughing, vomiting and weight loss.

"Unfortunately, sudden death does occur in a fair number of cats, thought to be due to blood clots caused by the disease," she says. "Owners of both dogs and cats should be vigilant for any signs of respiratory disease."

Jayaram thinks that recent climatic trends toward warmer, wetter, "mosquito friendly" weather and milder winters will lead to an increase in heartworm disease in Southern New England, if owners fail to take prevention measures.

She says that compounding the problem is the fact that the availability of the most effective drug used to treat the disease is currently limited because of a scarcity of the raw materials required to manufacture the pharmaceutical.

"There has also been data showing that cross-state movement of dogs for adoption purposes has led to the spread of disease in areas where heartworm was previously very low. This was found to be true especially after Hurricane Katrina, when many dogs from the Gulf, where heartworm is endemic due to the weather conditions, were sent to shelters up north."

Michael Patnaude, a senior research biologist at Smithers Viscient Laboratories in Wareham, urges pet owners to remove standing water from birdbaths and containers where rainwater can collect. These areas become prime breeding grounds for mosquitoes.

Noting that there are 26 species of the pesky insects that carry heartworm, Patnaude, like both veterinarians, urges pet owners to remain vigilant throughout the year.

"They are all out at different times," he says.