Heartworm is a parasitic worm that lives in the heart and pulmonary arteries of an infected animal. The worms travel through the bloodstream—harming arteries and vital organs as they go—ultimately completing their journey to the vessels of the lung and the heart chamber about six months after the initial infection. Several hundred worms can live in one dog for five to seven years.
Heartworm disease is serious and can be fatal.
Symptoms of heartworm can include:
- Labored breathing
- Weight loss, listlessness and fatigue after only moderate exercise
- Some dogs exhibit no symptoms at all until late stages of infection
- Heartworms are transmitted from animal to animal by mosquitoes.
- An animal must carry at least two heartworms (a male and a female) in order for female heartworms to reproduce.
- Females produce babies called “microfilaria,” which are shed into an animal’s bloodstream but are not capable of directly causing heartworm without first passing through a mosquito.
- Microfilariae must be taken up by biting mosquitoes, and transform into infective larvae over a two-week period inside the insect.
- When a mosquito next bites a susceptible animal, the infective larvae enter the tissues and begin a migration into the blood vessels.
- Heartworms enter an animal’s bloodstream as tiny, invisible larvae, but can reach lengths of more than twelve inches at maturity.
Heartworm disease is diagnosed by examination, radiographs or ultrasound, and a veterinarian-administered blood test.
All dogs should be routinely screened with a blood test for heartworm either annually in spring or before being placed on a new prescription for a heartworm preventative.
- Heartworm is easily preventable with an inexpensive, chewable pill or topical medication available as a vet’s prescription. The pills or topical are usually administered monthly and can be given to dogs under 6 months of age without a blood test. Older animals must be screened for the disease prior to starting medication.
- The American Heartworm Society recommends keeping your dog on the medication all year long. Not only does this avoid errors, but many of the products also prevent other intestinal parasites.