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Heartworm Facts

    • Has been diagnosed in all 50 states
    • Transmitted by mosquitoes, requires ideal temperature and humidity
    • Adults travel to the pulmonary arteries and the heart
    • Adults produce small larvae (microfilaria), which circulate in the blood and are consumed by mosquitoes during a blood meal
    • Microfilaria develops into stage 3 larvae within the mosquito, which is the larvae that is infectious upon a blood meal on a new host.
    • From exposure, to development of an adult worm takes 6 months.
    • Cough
    • Exercise intolerance
    • Abnormal lung sounds
    • Enlarged liver
    • Fluid accumulation on the abdomen
    Human Health Concern: None
    Monthly Preventative:
    • A monthly oral heartworm preventative (Heartgard = ivermectin, interceptor/sentinel = milbemycin oximine, revolution = selamectin, advantage multi = moxidectin, etc) is recommended to kill any possible heartworm larvae that a dog/cat is exposed to within the last 4 weeks.
    • The preventative is effective at killing larvae within 5-6 weeks of exposure, any other heartworms that the dog may have been exposed to will NOT be treated, and will also NOT display a positive when testing for heartworm.
    • Therefore, if any doses are missed at any time of year, it is recommended to switch to a preventative that is safe (heartgard, revolution, advantage multi) in the event that a dog acquires an adult heartworm infection
    Routine Annual Testing: Even if a dog is on a monthly preventative year round, it is strongly recommended to test annually for adult heartworms. Cats only require an initial Ab/Ag test, and then can remain on preventative. 
      If any adult dog becomes positive for heartworm, it is very important for this dog to be evaluated by a veterinarian. Depending on the severity of disease, x-rays or an echocardiogram may be required to evaluate the extent of the changes to the heart
      The American Heartworm Society recommends that dog be placed on a macrolytic lactone (Heartgard = Ivermectin) for 2-3 months prior to giving adulticide treatment. Because the adulticide treatment (Melarsomine) only kills heartworms greater than 4 months old, there is the potential for migrating 2-4 month old heartworm larvae to escape treatment and inhabit the patient’s heart.
      Melarsomine: Deep intramuscular injections into epaxial (back) muscles is the ONLY treatment approved by the FDA for adult heartworms. This is often a very painful injection, and mild swelling and soreness can persist for days afterward
        3 dose protocol: One injection, followed by a pair of injections 24 hours apart at least 30 days later. This protocol will effectively treat 98% percent of adult dogs.During this entire period of adult worm treatment, keep patient on a macrolytic lactone to minimize worm burden and effectively treat circulating microfilaria.    
        It’s very important to restrict the activity of a heartworm positive dog during and after his heartworm treatment. Many adult worms take 4-6 weeks after treatment to die. It’s possible for the adult worms to die suddenly, and travel to the lungs (or rarely, other parts of the body) where they can cause severe inflammatory conditions. Therefore, heartworm positive dogs must have strict exercise restriction (ideally in a crate while not under direct supervision, and only short leash walks 2-3 times daily) for at least 4-6 weeks after treatment, but ideally until they become heartworm negative.
      Retesting: While some dogs may become heartworm negative (no more adult worm antigen) as soon as 2-3 months after treatment, it is recommended to wait at least 6-7 months before retesting.


Canine Heartworm