Dogs and Heartworms

0 Comments Posted by tcahvet in News on Friday, June 7th, 2013.



Mosquito season is starting so it is time to talk about heartworms. Canine heartworms (Dirofilaria immitis) are spread by larvae in the saliva of mosquitos. A mosquito takes a blood meal from an infected dog then spreads those larvae to the next dog it bites. Unfortunately, it is impossible to prevent all mosquito bites or to know which mosquito will be the one to infect your dog. That means we need to keep all dogs on preventatives year round in a humid, warm climate like it is here.

Let me explain a little bit more about the preventatives. There are several forms of preventatives: oral (Heartgard, Sentinel, Trifexis and others), topical (Revolution and Advantage) and injectable (Proheart 6 which has limited availability). These preventatives send a drug into the blood system which kills any larvae that the mosquitos have already injected. That means a preventative treats for last month’s mosquito bites, not against future bites. This is why it is so important to give the preventative every single month.

Heartworm tests are recommended yearly to check for any lapses in preventative. The test will not give a positive until there are adult worms, which takes about 6 months. The test involves placing 3-5 drops of blood on a test and waiting approximately 10 minutes for results. We do these tests in house so the results are in before your visit is over. Even if a dog is always kept on preventative we do a yearly blood test because the earlier heartworms are found and treated the easier it is on the dog.

After a dog is injected with larvae by the mosquito, those larvae circulate in the bloodstream and tissues as they grow. Once grown, the heartworms lodge in the heart and lungs. The dog won’t show any signs of illness until the worms cause damage to the heart and lungs. Those signs start as a cough and continue to inactivity and difficulty exercising. Once those signs are present the damage is usually permanent.

There is a treatment for dogs who already have heartworms. It is a drug, Immiticide, that when injected slowly kills the worms. This treatment can be very risky depending on the number of worms and how severe the damage is. This treatment has many steps and the dog has to be fully evaluated for any damage before the treatment begins. While it is recommended for most dogs with heartworms, we do treat each dog as an individual.

Several other species of mammals can get heartworms as well. Cats and humans can both get them. In cats, because they are not the worms “favorite” host they usually only get a couple of worms but the inflammation from them can be deadly. For this reason, cats should be on preventative as well. Cats will usually show signs of respiratory distress or fever when infected.

Heartworm prevention is much easier than heartworm treatment. For more information please call us at 305-238-2222. You can also learn more at

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