Heartworm Disease in Dogs
A serious, mosquito-transmitted parasitic disease affecting the heart and lungs - far safer and cheaper to prevent than to treat.
Overview
Heartworm disease is caused by Dirofilaria immitis, transmitted by mosquitoes. Adult worms live in the pulmonary arteries and heart, causing progressive cardiopulmonary damage. Monthly preventives are highly effective, which is why prevention is the cornerstone of managing this disease.
Clinical signs
- Often asymptomatic in early infection
- Coughing and exercise intolerance as disease progresses
- Decreased appetite and weight loss
- In severe, advanced disease (caval syndrome): sudden collapse and hemoglobinuria - a life-threatening emergency
Diagnosis
- In-clinic antigen testing (ELISA/SNAP test) for adult female worms
- Confirmatory microfilaria testing
- Chest radiographs and echocardiography to assess disease severity and stage
Treatment
- Staged adulticide therapy with melarsomine injections
- Strict exercise restriction throughout treatment - this is critical, since activity increases the risk of a fatal pulmonary blood clot as worms die
- Concurrent management of circulating microfilariae
- Resuming monthly heartworm prevention once treatment is complete
Prognosis
Good with appropriate staged treatment and strict activity restriction. Prognosis worsens with more advanced disease or caval syndrome. Monthly preventives are highly effective at preventing infection in the first place.
This page is general reference information for educational purposes. It is not a substitute for an individual clinical assessment, current formulary guidance, or the judgment of a licensed veterinarian treating a specific patient.
Frequently asked questions
Why is exercise restriction so strict during heartworm treatment?
As the adult worms die, fragments can travel to the lungs and cause a blockage in the pulmonary arteries. Physical activity increases blood flow and the risk of this being fatal, which is why strict rest is required for the full treatment period.
Is heartworm prevention really necessary year-round?
In most regions, yes - mosquito activity and regional risk can vary, but year-round prevention is generally recommended since it is far more effective and far less risky than treating an active infection.