Pet health: Heartworm Disease

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A veterinarian gives heartworm medication to a dog with pet insurance.

By: Dr. Fiona Caldwell
For Pets Best Insurance

Heartworm disease is a pet health condition that is becoming increasingly more prevalent in the United States. It has currently been documented in all 50 states and is most common in the Mississippi valley and southern US. Even if you and your dog don’t live in the south, heartworm prevention is very important anywhere to avert this serious pet health disease. Many pet insurance companies even offer limited coverage for testing and prevention with their wellness coverage.

Heartworm disease is a potentially fatal disease characterized by parasitic worms that live in the heart and arteries in the lungs. The worms are a type of roundworm or nematode called filarids, and any age or breed of dog can be susceptible.

Filarids require an intermediate host to spread the worm from animal to animal. This intermediate host is the mosquito. This means that dogs can’t catch heartworm from causal contact with an infected dog, rather, they have to be bitten by an infected mosquito. Regions with the most mosquitoes tend to have the most incidences of heartworm disease.

Heartworms have a very interesting lifecycle. Like most parasites, they have a larval phase and an adult worm phase, but they also have a phase called microfilaria. The complete life cycle cannot take place in the dog’s body, but has to occur in the mosquito. This means dogs can’t ‘re-infect’ themselves, once the microfilaria turn into adults, the adults can’t replicate without using a mosquito as an intermediate host.

The larva is the infective phase of heartworm disease and is carried by the mosquitoes. The larva matures into adult worms, which in turn, produce millions of microfilaria that travel through the blood stream. Microfilaria cannot turn into the infective larval phase unless a mosquito takes a blood meal that has microfilaria in it. The microfilaria requires 10 to 30 days to turn into the infective larval phase. When the mosquito bites another dog, it can transmit the infective larval phase that once again turns into mature adult heartworms.

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Treatment for this disease is costly and difficult. There are medications available that will kill the worms, but the heartworms have nowhere to safely go in the body after dying. Dead worms in the arteries of the lungs and in the heart pose a serious risk for the patient. The best method to keep your dog healthy is focus on preventing this disease. Most veterinarians agree that monthly heartworm preventatives are important for any pet that spends time outside and could be bitten by a mosquito.

Heartworm preventative generally takes the form of a monthly product that either is poured on the skin, or a tablet taken orally. Heartworm preventatives should be in prescription form, and therefore must be purchased at or through a veterinarian’s office, or certified veterinary pharmacy. If you are considering keeping your pet on a heartworm preventative, contact your veterinarian with any additional questions.

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