It's a devastating, debilitating illness found in every corner of the United States. So why, despite the fact that the disease is easily preventable, are millions of dogs, cats, and other animals across the nation heartworm-positive?
According to Dr. Amy Attas, V.M.D., founder and owner of CityPets, a veterinary house call practice in New York City, pet caregivers often don't realize that heartworm is something that could affect their pet. Others are deterred by the cost of the preventative medicine.
But, despite their constraints, caregivers simply can't afford to wait until this indiscriminate illness strikes their pet before taking action.
"Heartworm is a common disease, and treatment is costly and dangerous," says Nancy Peterson, issues specialist for Companion Animals at The HSUS. "Educating pet owners about heartworm prevention is good medicine."
Attas agrees. "This is a devastating, even fatal, disease that we can safely and inexpensively prevent. Without prevention, animals are exposed to this disease which, in its early stages, has no symptoms."
Heartworm is transmitted to animals through a bite from a mosquito containing the infected larval form of the heartworm. When an animal is infected, the heartworm larva can grow and develop into worms. These worms live inside blood vessels within and surrounding the heart and lungs. The adult worms mate inside the blood vessels, and their offspring -- which are called microfilaria -- circulate in the bloodstream. These microfilaria can be picked up by another biting mosquito, and then passed to another animal.
The disease can be easily prevented, but it does require a visit to a veterinarian. Dogs must be tested to ensure they don't have heartworm before putting them on preventative medication. By federal law, heartworm preventative medicine is only available through a prescription. Pet caretakers should consult with a vet to discuss their pet's individual needs.
Vets may tailor medication depending on the type of pet. Although cats can be infected, heartworm is typically more serious in dogs.
"Cats can also become infected with heartworms, and in some cases the disease progresses in the same way as it does in dogs, where the worms settle in the blood vessels and heart," says Attas. "However, because the parasite is not as well adapted to cats, sometimes the immature worm is unable to complete its migration."
Another consideration is geographic location. In some parts of the country heartworm is much more common in certain areas than in others.
"Although heartworm infection has been found in dogs in all 50 states, it is much more prevalent around the Atlantic and Gulf Coasts," says Attas. "The temperature and humidity in these regions support mosquito populations, which are the vectors that transmit this disease."
Once infected, animals with heartworm can be treated if the disease is caught in time, but there are several drawbacks.
"The treatment, although effective, is painful, expensive, and can have side effects," says Attas.
If the disease goes untreated, the results can be fatal.
"In dogs, the adult worms live in the cardiovascular system and cause a great deal of physical damage. Severely affected dogs develop heart failure because the physical presence of a large number of these worms can actually obstruct blood flow through the heart. Untreated heartworm disease causes serious cardiovascular complications which can be fatal."
Pet caregivers can start making heartworm prevention a priority by scheduling an appointment with a veterinarian in their area.
Rebecca Simmons is the outreach communications coordinator for the Companion Animals section of The HSUS.