Adopting a Heartworm Positive Dog

Very often Petey and Furends will rescue dogs that have heartworm disease. While heartworm disease is expensive to treat, we believe that these dogs deserve the chance at a better life. 

Once heartworm disease is treated, a dog can go on to lead a perfectly healthy life. To make it easier for adopters to navigate, we have compiled an overview of heartworm disease and highlighted our treatment protocol. 

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Heartworm is a preventable, but serious and potentially fatal, parasite that primarily infects dogs, cats, and ferrets. All dogs and cats are susceptible to heartworm infection.

Geographically, heartworms are a potential threat in every state, as well as in many other countries around the world. All dogs, regardless of age, sex, or living environment, are susceptible to heartworm infection. Indoor, as well as outdoor, cats are also at risk for the disease. 

Transmission:

  • Heartworm has been diagnosed in all 50 states. 

  • Transmission occurs by mosquitoes, which requires ideal temperature and humidity (this is why you tend to see more cases in southern states).

  • Adult worms travel to the pulmonary arteries but can also inhabit the right side of the heart.

  • Adult worms produce small larvae (microfilaria), which circulate in the blood and are consumed by mosquitoes during a blood meal.

  • Microfilaria develop into stage 3 larvae within the mosquito, which are the larvae that are infectious upon a blood meal on a new host. 

  • From exposure to development of an adult worm takes 6 months. This is why puppies under 6 months are NOT tested for heartworm.

Signs: 

  • Cough 

  • Exercise intolerance 

  • Abnormal lung sounds 

  • Collapse 

  • Enlarged liver 

  • Fluid accumulation on the abdomen

Testing: 

  • Routine Annual Testing - the 3DX or 4DX test – is the easiest test to evaluate for heartworms,  and it also tests for the following tick-borne illnesses: Lyme, ehrlichia, anaplasmosis. 

  • The standard testing looks for female adult heartworm female antigen (small pieces of adult worm). This is the standard for dogs. The only shortfall is that this tests for only an active ADULT FEMALE infection, and will not detect other possible migrating heartworms. 

  • Fresh blood slide or knots test is used to evaluate for circulating microfilaria. 

  • Even if a dog is on a monthly preventative year-round, it is strongly recommended to test annually for adult heartworms. 

Preventative: 

  • A monthly oral heartworm preventative is recommended to kill any possible heartworm larvae that a dog/cat is exposed to within the last 4 weeks.  

Treatment: 

  • The dog is placed on Heartgard (ivermectin) for 2 months prior to giving treatment. Because the treatment kills only heartworms greater than 4 months old, there is the potential for migrating 2- to 4-month-old heartworm larvae to escape treatment and inhabit the patient’s heart. Heartgard will help minimize that.

  • Deep intramuscular injections into epaxial (back) muscles of immiticide (melarsomine) 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 month of doxycycline followed by one injection, followed by a pair of injections 24 hours apart at least 30 days later. This protocol will effectively treat 99% of adult dogs. 

    • 2 dose protocol: One month of doxycycline followed by a pair of injections 24 hours apart at least 30 days later. This protocol will effectively treat 90% of adult dogs. Please note this is the treatment plan that Petey and Furends will do for dogs unless heartworm is more advanced. 

  • Alternate protocols: If a dog can’t receive immiticide injections, another option is a higher dose of ivermectin with or without doxycycline. 

    • It’s very important to restrict the activity of a heartworm-positive dog during and after their 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. 

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Petey and Furends