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Heartworm Disease

Heartworm disease is a serious and potentially fatal disease of dogs, cats and ferrets. It is transmitted to our pets by mosquitoes which are prevalent most of the year in the southern United States. There are several FDA approved heartworm preventative medications on the market which makes this a completely preventable disease.

Dogs are the most common reservoir of heartworm disease. Mosquitoes bite a heartworm positive dog and pick up baby heartworms from the dog. In the mosquito the baby heartworms transform into an infective larva. When this mosquito bites another animal (dog, cat or ferret) it injects the larva into the animal. It will take about 6 months for these larvae to mature into adult heartworms which will take up residence in the pulmonary artery and the heart. If a male and female heartworm is present, then they will produce more microfilaria or baby heartworms and the cycle begins again.

Heartworm Life Cycle

Heartworm life cycle in cats and dogs

The most common symptom of heartworm disease in dogs is coughing. If the dog has a lot of adult worms present they may show signs of respiratory distress (difficulty breathing), decreased activity, or stop eating. As the disease progresses the dog may go into heart failure making treatment much riskier. Ferrets will usually have the same symptoms as dogs. Cats tend to have more problems from the immature stages of the heartworm and are much more difficult to diagnose. Cats may show signs of coughing, respiratory distress or vomiting. Some cats may just acutely die without ever showing any symptoms.

There are several tests available to test for heartworms in dogs which are very sensitive and accurate. These tests can also be used in cats and ferrets but are less accurate due to the small number of worms that are present in these animals. In these pets other tests can be run to help the veterinarian determine if heartworms are present.

There are no current treatments for adult heartworms in cats or ferrets but symptoms can be controlled in some pets with steroids. For dogs, the adult heartworms are treated with a drug called Immiticideā„¢. It is given as 2 or more injections. The treatment can be expensive but is very effective. As part of the heartworm treatment animals will be given heartworm preventatives and must stay on them for the rest of their life to prevent them from being reinfected. It is crucial that dogs are kept calm and are confined throughout heartworm treatment (up to 8 weeks) or severe even fatal complications can arise.


Alex "Steve" Steverson, DVM

April 1, 2016

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