Heartworm Disease
Heartworm disease is caused by the parasitic worm Dirofilaria immitis, transmitted through mosquito bites. Adult worms reside in the pulmonary arteries and right heart, causing progressive cardiovascular and pulmonary damage. Dogs are the definitive host; cats are atypical hosts with different disease manifestation.
Symptoms & Signs
- Dogs: persistent cough, exercise intolerance, fatigue, decreased appetite, weight loss, heart failure
- Cats: coughing, asthma-like attacks, vomiting, weight loss, sudden death
- Advanced: caval syndrome, ascites, collapse
Causes & Risk Factors
Transmitted by mosquitoes carrying infective larvae (L3). After injection into the host, larvae migrate through tissues, reaching the pulmonary vasculature in 6 months. Adult worms (up to 30cm) cause mechanical obstruction and inflammatory damage to pulmonary arteries.
Diagnosis
Dogs: antigen testing (detects adult female worms), microfilaria testing, thoracic radiographs, echocardiography. Cats: antibody testing (exposure), antigen testing (adult worms), radiographs. Staging determines treatment approach.
Treatment
Dogs: melarsomine (Immiticide) injections to kill adults, doxycycline to weaken worms, exercise restriction, prednisone for inflammation. Slow-kill (monthly preventive only) is not recommended. Cats: no approved adulticide; supportive care and prevention.
Prevention
Year-round monthly heartworm preventives (ivermectin, milbemycin, moxidectin, selamectin). Annual testing to confirm prevention efficacy. Mosquito control measures. Prevention is far safer and more cost-effective than treatment.
Prognosis
Dogs with mild-moderate disease: good with proper treatment. Severe disease (caval syndrome): guarded. Cats: unpredictable; sudden death can occur. Prevention is critical as treatment carries significant risk.