Heartworm Disease in Dogs and Cats

As the weather becomes warmer and mosquitoes begin to appear, each and every dog and cat owner (yes I did say cat owner) should become concerned about a very easily transmissible, potentially fatal, blood born parasitic infestation known as heartworm disease.

I will begin by discussing canine heartworm disease and return to a discussion of information specific to the cat at the end of the article. Cat owners are advised not skip to the end of the article because most of what I say about heartworm disease in dogs also pertains to cats. When a dog gets bitten by a mosquito carrying heartworms, it usually takes a minimum of 5 months before there is evidence of the heartworm larvae in the dog’s blood, however, outward signs of the disease may take far longer to become obvious and, in fact, may never be outwardly detectable in those dogs with mild infestations. Dogs with just a few worms in their heart may live a normal life, however, dogs with a more abundant worm load may eventually develop a cough and then fatal respiratory distress. The point to be made here is that prevention and/or early detection is the answer to protecting your dog and your neighbor’s dog from heartworm disease. If you wait until your dog is showing signs of illness before you see your veterinarian you may have waited too long.

When a mosquito bites a heartworm infested dog it sucks blood which contains the microscopic heartworm larva. When the mosquito then bites another animal, these larva are regurgitated into the unsuspecting victim. These larva start growing in the new host animal and over the next 5-7 months may reach 14 inches in length and may number as high as 50 or 60 worms. Heartworms in dogs are most often found in the heart proper and in the large vessels entering and exiting the heart where they reduce blood flow through the lungs and liver. Because Heartworm disease is so easily transmitted, every dog , whether kept inside or out, should be blood tested yearly for the disease. Dogs which are confined to their backyard, with no dogs for blocks around, can still easily contract heartworm disease. Even dogs kept inside 95% of the time are at risk because mosquitoes readily enter houses. Dogs with thick hair coats, such as Samoyed and Malamutes, are in no way adequately protected from the bite of infected mosquitoes. Heartworm testing helps veterinarians to identify Heartworm infected dogs in the early stages of the disease before obvious symptoms appear and before the disease spreads to other neighborhood dogs. If the disease is detected early, the chance for successful treatment is greatly enhanced. With the exception of young pups, any dog that is to be put on Heartworm preventive should be blood tested yearly and found free of heartworms before preventive medicine can be dispensed by a veterinarian. Owners that elect not to give their pet heartworm preventive should have their unprotected dog heartworm tested semi-annually. By checking these pets every 6 months an infected animal will be detected at the earliest possible time.

Although the incidence of heartworm disease in cats is much less than dogs, if a cat contracts heartworm disease there is no safe medical treatment like there is in dogs, and the disease is much more likely to prove fatal. Furthermore, a single heartworm can produce a fatal vascular obstruction in a cat compared to the need for 25 or 30 worms in a dog. Consequently, a cat that contracts heartworms is much more likely to die from this disease than is a dog. For these 2 reasons Heartworm prevention becomes even more important for cats than dogs.

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