Heartworm: The Deadliest Worm

Although all of the worm and worm-like parasites we cover in this article can theoretically lead to death if untreated, heartworm ranks as the most dangerous. In fact, it's probably the most deadly parasite that can affect your dog. Heartworm was once mostly found in hot and humid areas, and in dogs who spent a lot of time in the woods, but it's now running rampant across the United States. And it all begins with a mosquito bite.

When a dog is bitten by a mosquito infected with heartworm larvae, the larvae enters his skin and begins its lifecycle, eventually riding through the dog's bloodstream to the right side of the heart as well as the lungs and surrounding blood vessels. It takes about seven months for the worm to mature. If not detected, the growing population of adult worms can create a mass that blocks blood flow and ultimately cause organ failure. The adult worms also breed and produce offspring called microfilaria. They circulate in the dog's bloodstream, and can be sucked up by a mosquito that bites him. Within a few weeks, the microfilaria develop into infectious larvae. The next time the mosquito bites another dog, these larvae are passed along and the cycle begins all over again.

Dogs infested with heartworms may go for years without showing any symptoms of infection, and adult heartworms can live for up to seven years. An early sign of heartworm infection is a deep, soft cough that gets worse with exertion. As the cycle progresses, the dog can become lethargic, loses weight, and may cough up blood. In the later stages of heartworm disease, dogs can retain fluid and develop congestive heart failure. Without treatment, they'll die.

The good news is that heartworm infestations are completely preventable. Your vet can recommend a preventative -- usually a monthly chewable pill -- to give your dog so that you'll never have to worry about this deadly disease. Heartworm infestations are diagnosed through a blood test, and the treatment for a full-blown case of heartworms is very stressful. It consists of several painful arsenic-based injections, which kill and break up the adult worms into tiny pieces. A dog undergoing heartworm treatment must be kept confined and quiet, because these worm pieces can block vessels during strenuous exercise and cause death.

Many heartworm preventative medications also protect against other worm infestations, including tapeworms and whipworms. Next, we'll look at how flea bites and just being in the wrong place at the wrong time can lead to more intestinal worms.