General Information about Heartworm Disease

Heartworms have become so common in the United States that many people know all-too-well the dangers imposed by this parasite. Heartworm disease is caused by the heartworm, Dirofilaria immitis, which lives in the right side of the heart, and the nearby large vessels (pulmonary arteries). Heartworm disease does damage to the heart and lungs, but also affects other major organs.

Female worms produce large numbers of microscopic, immature heartworms that circulate in the blood. The immature worms (microfilariae) are taken up with the blood when a mosquito feeds on an infected pet. After living in the mosquito for 10-14 days, the microfilariae can then infect other pets that the mosquito feeds on. The microfilariae eventually will migrate to the heart where they develop into adult heartworms. The adult heartworms produce new microfilariae within 3 months.

While heartworm disease is most commonly associated with dogs, the cardiologist at Texas A&M University College of Veterinary Medicine is recommending heartworm prevention for cats, too. Necropsy (autopsy) has shown incidences of 10% to 25% of cats have been infected with heartworms, with the variable being the length of time in which the cat is allowed to be outdoors, and at which time the cat is allowed to be outside (dusk/dawn or afternoon, etc).

Most cases of heartworms are diagnosed with a simple blood screening by detecting microfilariae in the blood, while other cases are diagnosed with a combination of blood tests and x-rays. Failure to treat heartworm disease may result in heart failure and/or serious disease of the liver and kidneys. Untreated heartworm disease is usually fatal.

Highly effective medication, such as Heartgard PlusŪ, is available to prevent heartworm disease. Mosquito control with repellents and electronic insect killers is helpful, but should never be the sole means of prevention.