The Importance of Giving Heartworm Prevention All Year in Oklahoma

posted October 15th, 2010 by
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BY MARK SHACKELFORD, DVM

Mosquitoes transmit heartworm disease, which affects both dogs and cats. Due to our temperate climate in Oklahoma, mosquitoes can be seen at various times all year long. I have swatted mosquitoes in my home in January and February, which shows how resilient these insects can be. We can have one or two days of above freezing temperatures that will cause otherwise dormant mosquito eggs and pupae to hatch and become active.

When a mosquito bites an animal, the larva, or immature form of the heartworm is deposited on the skin, and from there makes a journey to the bloodstream, which takes 30 days, eventually taking it to the heart, where it will mature to an adult heartworm. This is the reason that heartworm preventatives can be given once per month…they kill the immature heartworm that is migrating through the skin. But, once the larva reaches the bloodstream, the preventative is ineffective. Therefore, it is very important to give the heartworm medication on a strict monthly schedule.

Heartworm disease can be hidden for a long time, sometimes taking years before symptoms appear. One of the first things that dog owners will notice is a decrease in exercise tolerance, which means there is a shorter period before the dog gets tired and stops playing or running. As the disease progresses, a chronic cough may be heard and an even greater exercise intolerance may be noticed. Other symptoms may include weight loss, lethargy due to pneumonia, and signs associated with congestive heart disease. Cats will have episodes of sneezing and coughing, and may eat less and become more isolated from their owners.

Annual heartworm testing for dogs is very important, even if you are giving heartworm preventative every month of the year. Sometimes the preventative will be given late or incorrectly applied to the skin, as in the case of topical products. This is why a heartworm test should be performed yearly in conjunction with a check up and vaccinations.

Treatment for active heartworm infection in dogs consists of a series of injections given in the muscle of the back. This is usually a painful procedure but the pain can be controlled with analgesics and other medications that are given at the time of treatment and at home for several days afterwards. In our hospital, we will pre-treat with an antibiotic for a month and will have the client start pain medication 2-3 days before the injections start. We will give injections on one day, then wait one month and give injections for 2 days in a row. This makes a total treatment time of 2 months, which is uncomfortable for the dog and can be expensive for the owner. Unfortunately, there is no treatment for heartworms for the cat, simply because the drugs are too toxic.

There are many types of heartworm preventatives available for both the dog and the cat. When I first started practicing veterinary medicine, the only available heartworm preventatives were pills that were given on a daily basis. Now we have medications that are given or applied monthly, and even an injection that is administered every six months. We have monthly oral heartworm preventatives in combination with intestinal wormers, and we have oral preventatives in combination with intestinal wormers that also can inhibit the hatching of flea eggs. There are also products available, that, when applied to the skin, will prevent heartworms, intestinal worms, and will kill fleas, their larvae, and their eggs. Your veterinarian will be able to advise you on what is the best product for your pet.

Giving heartworm preventative all year is very important for the health of your pet due to the prevalence of mosquitoes and other parasites in Oklahoma. Yearly testing for dogs is also necessary to ensure that treatment will never have to be a necessity for these important companions and family members.

Mark Shackelford
Mark Shackelford is a co-owner and veterinarian at the 15th Street Vet Group, Tulsa.

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