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Year in Review: Heartworm Disease

To follow up on the recent review of tick diseases, I would like to take a minute to discuss heartworm disease. Heartworm is exactly what is sounds like - a parasitic worm that lives in the heart. The worms can grow up to 16 inches long and one dog can host as many as 250 worms (with heavy infections). The worms take about 6 months to reach maturity from transmission to reproduction.



This disease is transmitted by mosquitoes who pick up juvenile worms from one dog/cat and transmit it to another. It is most prevalent therefore, where there are many mosquitoes. I remember being a veterinary assistant (before vet school) and telling people that they didn't need to worry about heartworm disease unless they were taking their dogs to the mountains. Guess what? That is not the case any more. Mosquito populations are on the rise, and our local coyote population is acting as a reservoir.


According to the companion animal parasite council "For the fourth year in a row, cases of heartworm infections are forecasted to be above normal across virtually the entire United States....Nationally, prevalence rates have risen each of the last five years and are now up 20% from 2013 levels."


In 2012, San Diego county had 107 cases of canine heartworm. This year, that number is up to 204. How do we compare to other areas around the country? Anchorage, Alaska had only 5 cases of heartworm disease. Dallas, Texas had 2,151 cases. Obviously we have more dogs than Alaska, and not as many mosquitos as Texas. But it is here. These are considerations to take into account if you plan on traveling or moving with your pets.


How is heartworm disease treated? If you adopt a dog with heartworm disease, or find that your dog has contracted it, it can be scary. Heartworm disease can be fatal if left untreated, but thankfully the American Heartworm society has put together an excellent treatment protocol to rid dogs of the parasite. It is a lengthy process that involves preparation, antibiotic treatment, arsenic based anti-parasitic injections, and months of rest. Unfortunately for cats there is no treatment, and often the first sign of disease is sudden death.


Prevention of this disease is much better than treatment. Prevention is a low dose of medication that will kill any larval worms that a pet contracted in the last month. The medication needed to kill the "juvenile" worms is much more safe than the medication needed to kill mature worms. The monthly pill or topical medications are in the body for one day and then are metabolized and leave.


Annual testing is recommended to make sure that your pet is clear of disease, even when on a preventative. Testing in dogs checks for mature pregnant worms, which take time to develop. This year's test picks up last year's infection. In cats, we test for antibodies against the worms. This still takes time to develop in the body.


In San Diego, it is recommended to be on prevention throughout the year. We do not have seasons and have mosquitoes year round (just like fleas).


Have any questions about heartworm disease? Just send an email.



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