Heartworm disease, a potentially life-threatening condition, is found in geographic areas that house mosquitoes. While treatment is available for heartworm infection in dogs, prevention is much safer and without side effects. To understand more about how heartworm infection affects your pet, let’s begin by looking inside the heart of an infected dog:
Adult heartworms live and reproduce in the heart and large blood vessels entering the lungs of an infected dog. Mature female heartworms pass their offspring (called microfilaria) into the dog’s bloodstream to circulate throughout the body. The transfer of infection to another susceptible animal begins when a mosquito takes a blood meal from a heartworm-infected dog. Once inside the mosquito, the microfilariae spend the next 30 days maturing into an infective stage. Maturation of the microfilariae to infective larvae within the mosquito is required for transmission of heartworm infection. At the next blood meal, the mosquito injects the infective larvae into the skin of a naïve dog. After a short time in the skin, the larvae migrate through the body to finally land in the pulmonary arteries to mature into adults 5-6 months later and restart the lifecycle. The entire life cycle takes 6-8 months to complete depending on environmental conditions.
Symptoms of heartworm infection vary by the stage of the disease. The American Heartworm Society classifies heartworm infection in dogs to determine the extent of the disease, develop the safest treatment protocol and monitor therapy.
- Stage 1: Early infection/Mild disease. Symptoms range from asymptomatic to a cough
- Stage 2: Moderate disease. Cough, exercise intolerance
- Stage 3: Severe disease. Cough, exercise intolerance, labored breathing, collapse, death
- Stage 4: Caval syndrome. Large worm burden that impairs blood flow to the heart causing abdominal distension, swelling of the limbs, weight loss, weakness and/or death
There are two blood tests available for detection of heartworm infection:
1. Heartworm Antigen test: detects the presence of adult female worms.
2. Microfilaria (Knott’s) test: visualizes the microfilariae (produced by the adult heartworms) in the blood.
Both of these tests require a mature infection to be accurate. Testing a dog for heartworm infection during the early stages of infection will lead to a false negative result. Repeat testing several months later may be needed to confirm results.
Treatment for heartworm infection requires a series of injections to kill the adult heartworms. Based on your pet’s staging, your veterinarian will develop the safest treatment protocol. The safest, most effective treatment for heartworm disease is prevention: treat the infection before the worms mature and lead to disease. Monthly, year-round prophylactic medication prevents this life-threatening disease.