Heartworm Disease

Heartworm Disease

Species: Dog

Breeds Affected: All Breeds (mosquito exposure is the key risk; more common in warm, humid regions)

Heartworm disease is caused by the parasite Dirofilaria immitis, a worm transmitted by mosquitoes. The larvae migrate and mature within the dog's body, eventually residing as adult worms in the heart and pulmonary arteries. Dozens of worms can infest a dog, causing severe damage to the heart, lungs, and blood vessels over time. If untreated, heartworm disease can be fatal.

• In early stages
• dogs may show no signs. As the worms grow and multiply
• signs can include coughing and labored breathing
• exercise intolerance (get tired or faint after mild exercise)
• weight loss
• and lethargy. In advanced cases
• heart failure signs develop: fluid accumulation in the abdomen
• collapse episodes
• or pale gums. Some cases of heavy worm burden lead to Caval Syndrome – a life-threatening blockage of blood flow causing sudden collapse and dark brown urine.

Treatment of heartworm disease involves killing the worms with a series of adulticide injections and managing any complications. The standard treatment uses melarsomine injections (an arsenical drug) given intramuscularly to kill adult worms. This is done in a staged protocol (usually two to three injections over a month). The dog must be kept on strict exercise restriction for several weeks to prevent complications from dying worms. Prior to adulticide treatment, dogs are often stabilized with 4–8 weeks of an antibiotic (doxycycline) to eliminate Wolbachia bacteria (symbionts of the worm) and a heartworm preventive to kill larval stages. Supportive care (corticosteroids to reduce inflammation, cage rest) is used to reduce treatment risks.

Adulticide medication: Melarsomine dihydrochloride (brand Immiticide) is the FDA-approved drug that kills adult heartworms. It is administered via deep intramuscular injection in the lumbar muscles. Along with melarsomine, treatment protocols include other medications: Macrocyclic lactone heartworm preventives (like ivermectin) are given to kill microfilariae (larval worms) before and after adulticide therapy. Doxycycline is given prior to treatment to weaken the worms by eliminating their Wolbachia bacteria. Additionally, prednisone or other steroids may be used short-term to reduce the risk of thromboembolism (inflammatory reaction to dying worms). After successful treatment, the dog must remain on monthly heartworm preventive for life.