Preventing Heartworm in Dogs

Of all the conditions that can strike the dogs we love, heartworm is perhaps the most tragic because it is almost completely avoidable through preventative medication.

The Heartworm Life Cycle

Heartworm is a parasitic roundworm called Dirofilaria immitis. Infection is spread through mosquito bites, and affects not only dogs but also cats, wolves, coyotes, foxes, ferrets, sea lions and in rare cases, even humans. This parasite gets its name from the fact that in its final life stage, it resides in the heart of its host where it eventually causes congestive heart failure and death.

Heartworms give birth to live young and go though a series of life stages. Stage one heartworms, called microfilariae, circulate in the bloodstream of the host for up to two years, requiring the bite of a mosquito to progress to the next stage.

After being ingested by the bloodsucking mosquito, the heartworms molt until they reach the third larval stage. This stage is known as the infective stage because the larvae then migrate to the head of the mosquito, where they await the opportunity to infect another host when the mosquito feeds. As the mosquito drinks the blood of its victim, the third stage larvae are deposited into a new host.

After growing and molting to a forth stage, they then travel to the chest and abdomen muscles of the host. Eventually they molt to the fifth stage, enter the bloodstream and lodge in the arteries of the lungs. As soon as seven months after initial infection, adult worms mate and begin to reproduce.

Symptoms of Heartworm Infection

Many dogs show no symptoms of infection, even after the heartworms inside them have matured. Early symptoms include coughing, and exhaustion from exercise. By the time these seemingly mild symptoms appear, the dog is very sick. Eventually the dog will experience weight loss, bringing up blood with a cough, fainting, and at the end, congestive heart failure. Once infected with heartworm, treatment is painful, risky and expensive. Sometimes lives are saved, however treatment often is too late.

Treating Heartworm

The best way to treat heartworm is to see that your dog is never infected with it. Your veterinarian can prescribe medication, which will kill any early stage heartworm larvae your dog comes in contact with, preventing this deadly infection from ever taking hold. Heartworm prevention medicine is available both in pills and a chewable form with a flavor that appeals to most dogs.

To be effective, the medicine must be given once a month consistently. In warmer climates it should be given year round, and in climates with cold “mosquito-free” winters, it may be given only during the spring, summer and fall. Every year, your veterinarian should perform a blood test to be sure that your dog has not contracted heartworm before the prescription for preventative medication is renewed. By simply remembering a monthly pill and annual blood test, the dog you love need never suffer a painful and premature death from heartworm infection.