Heartworm disease is a significant and potentially fatal disease of primarily dogs but also cats. It is also one of the most preventable diseases that veterinary medicine has to offer. The disease occurs as worms live within the heart and vessels of the lung leading to heart disease and potentially heart failure.
The lifecycle of the heartworm (Dirofilaria immitis) is long and complex. EVERY DOG AND CAT, BOTH INDOOR AND OUTDOOR ARE SUSCEPTIBLE. Heartworms are transmitted through mosquitoes. Without the mosquito, it is impossible to contract heartworms. In order to understand the lifecycle, we begin as the mosquito bites an infected dog. As the mosquito is feeding, it takes in the immature stages of the heartworm that is circulating in the animal's blood. These microscopic immature worms must further develop within the mouthparts of the mosquito. Unbeknownst to the mosquito, it finds a new animal to feed on. Once it begins feeding again on the new, uninfected animal, the immature worms are injected into the skin. It then travels in the body for approximately 4-6 months, maturing along the way, and finally reaching its final destination (the heart). Once in the heart, this mature adult worm will mate with another worm to produce more immature stages that circulate in the blood and wait to be taken in by another mosquito.
Diagnosis is primarily through blood tests which test for the antigen of the adult female worm as well as a drop of blood that harbors the microscopic, swimming immature stages. Radiographs may be performed in attempts to identify the severity of the disease. It is theoretically possible for there to be an infection with all male worms that produce no immature stages, but this is very unlikely.
Treatment is much safer now than it was even 10 years ago. A product known as Immiticide is injected in the lower back muscles 24 hours apart for 2 injections. This medicine is designed to slowly kill the mature worms over a 2-3 week period. Because of this time frame, IT IS IMPERATIVE THAT YOUR PET STAY CALM AND INACTIVE FOR AT LEAST 4 WEEKS. This is to prevent the premature death of worms that could serve as clots. After 4 weeks of rest, the patient will then receive another medicine to kill the immature stages. Another blood tests will then be performed within 2-3 months after therapy. If your pet is significantly ill with heartworms, your veterinarian may choose to perform and extended therapy.
Prevention is recommended for both dogs and cats every month of the year. Prevention is directed at killing the immature stages of the heartworm before they can mature into a young adult or adult worm. We perform heartworm test every year on dogs even if they are on the prevention.