How Is Heartworm Transmitted?

Heartworms afflict both dogs and cats.

Heartworms are a parasite that afflicts dogs and cats. They are thin, white worms that grow to more than 5 inches long. They are called heartworms because they congregate in the heart and the oxygen-rich arteries from the lungs to the heart. Heartworms are transmitted by mosquitoes that bite an infected dog or cat and then bite an uninfected animal. Heartworm disease is relatively simple and inexpensive to prevent. Treatment, on the other hand, is difficult, dangerous, lengthy and costly. But without treatment, an infected animal can die.

Heartworm Life Cycle

Adult heartworms produce hundreds of thousands of microscopic offspring known as microfilaria that circulate in the infected animal's bloodstream, according to the veterinarians at Placerville Veterinary Clinic. They don't develop further until they are in a mosquito's gut. When a mosquito takes blood, it also takes in microfilaria that will develop into heartworm larvae inside the mosquito over a span of around two weeks. The larvae congregate around the mosquito's mouthparts.

Mosquito Transmits Larvae

When the mosquito bites another animal, it passes some of the larvae into that animal's bloodstream, where they develop over a six-month time span into adult heartworms that repeat the life cycle in the new animal. According to Placerville Veterinary Clinic, mosquitoes are the only means of transmission for heartworms.

Heartworm Prevention

Several different heartworm preventive drugs are available for dogs and cats. Animals that go outside are at risk for getting heartworm, particularly when mosquito season starts. Animals should be tested for heartworm disease before giving preventive drugs. Heartworm prevention requires giving animals a monthly dose of the preventive medicine in pill or liquid form. These drugs act like a vaccine, killing the heartworm larvae before they can develop into adults, but have no effect on adult heartworms.

Heartworm Disease

Heartworms kill their host by clogging the heart and arteries to the point where blood cannot flow through. There are no symptoms of infection until the disease is well advanced. Then the symptoms are like those for congestive heart failure. According to Placerville Veterinary Clinic, treatment for dogs involves restricting activity, administering antibiotics to kill opportunistic bacteria, administering vermicidal drugs to kill the adult heartworms, administering preventives to kill their offspring and administering anti-inflammatory drugs to reduce swelling of the heart tissues. The heartworm-killing drugs can have painful side effects in dogs, and the complete course of treatment takes several months.

Outlook Grim for Cats

There are no drugs approved for treating heartworm disease in cats, according to the cat-care experts at Pawprints & Purrs. Veterinarians can try using the vermicidal drugs for dogs, but they present a high risk of fatal side effects in felines. Alternatively, the veterinarian can treat the cat's symptoms with oxygen therapy, anti-inflammatory drugs and diuretics. It can take a year or more for complete recovery, and symptomatic treatment must be kept up for that time.

References

• Placerville Veterinary Clinic: Heartworms and Heartworm Disease in Dogs and Cats
• Paws & Purrs Inc.: Heartworm in Cats