What is Heartworm Disease?

Heartworm disease is a serious and potentially fatal disease. Approximately 1 million pets in the US have heartworm disease. It’s caused by foot-long roundworms that settle into the heart, blood vessels, and lungs of an affected pet. These worms can cause severe lung disease, heart failure, and damage to other organs in the body. Heartworm disease can cause lasting damage to a dog’s health and quality of life even after the parasites are gone. It takes 6-7 months for larvae to mature to adulthood where it begins its reproduction cycle. A single heartworm can live up to seven years. 

Dogs are natural hosts for heartworms, meaning that heartworms live inside the dog mature into adults, mate, and produce offspring. Dogs can have several hundred worms in their body. Heartworm disease in cats is very different. Cats are atypical hosts for heartworms, meaning most worms in cats do not survive to the adult stage. Cats typically have just one to three worms. 

How do Pets Get Heartworm Disease?

Mosquitos are the most common carrier of heartworm and play an essential role in transmission. Female mosquitos pick up larvae in the bloodstream of infected animals and then transmit the larvae to the next animal it bites. Unfortunately, all it takes is one bite. Once inside the new host, it takes about 6 months for the larvae to develop into adult heartworms. Once mature, heartworms can live for 5-7 years in dogs and 2-3 years in cats. 

What are the Symptoms of Heartworm Disease?

Signs of Infection in Dogs: In the early stages of the disease, many dogs show few symptoms or no symptoms at all, making it almost impossible to notice in dogs, which is why testing is so important. The longer the infection persists, the more likely symptoms will develop. 

  • Coughing
  • Easily fatigued
  • Lethargic
  • Lack of interest in play or exercise
  • Decreased appetite
  • Weight loss

How can Heartworm Disease be Prevented?

Regular heartworm testing is key. All dogs should be tested annually for heartworm infection, which can be done during a routine visit or a low-cost Wellness Clinic, like Planned PEThood. Even when dogs are on heartworm prevention year-round, they should still be tested annually to ensure that the prevention is working. 

A monthly preventative is recommended and gives your dog the best chance of avoiding these parasites. Heartworm preventative is available only by prescription through a veterinarian. Some preventatives also protect against other types of parasites. 

Puppies under 7 months can be started on heartworm prevention without a test, but should then be tested 6 months after starting the preventative. Adult dogs over 7 months and dogs previously not on a preventative need to be tested prior to starting heartworm prevention. If there has been a lapse in prevention (one or more late or missed doses), dogs should be tested.

FAQ About Heartworm Preventatives:

Can Heartworm be Treated?

Yes, heartworm can be treated, but it is an expensive and complex process that is extremely tough on the dog. The earlier the disease is detected, the better. 

How Do Monthly Heartworm Preventatives Work?

Monthly preventatives work by eliminating any immature heartworm parasites. Because the preventative cannot effectively eliminate juvenile or adult larvae, it is important to administer heartworm on a strict schedule. 

Do I Need a Prescription for Heartworm Preventative?

Yes, the Food and Drug Administration (FDA) states that heartworm preventatives must be purchased from your veterinarian or with a prescription from a pet pharmacy. 

Are Heartworms More Common in Certain Areas of the US?

Heartworms have been found in all 50 states. Weather (temperature and humidity) and the presence of mosquito breeding areas both affect the level of risk of heartworm infection. 

Learn more about heartworm disease.