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Heartworm Life Cycle

Heartworm Life Cycle

Heartworms are roundworms that cause a severe, life-threatening infection in animals like dogs, cats, wolves, etc. This article throws light on their life cycle, and how to identify and treat an infection...
Kanika Khara
Heartworms are parasitic roundworms that can grow up to 14 inches long. The worms are often found residing in the right side of the animal's heart and arteries of the lungs. The infection spreads from animal to animal by mosquito bites. It causes potentially irreparable damage to the arteries, leading to heart failure, and, in extreme cases, also affects other body organs such as the liver and the kidneys. It prevents the heart from functioning properly, by causing blockages in blood vessels. Commonly found in dogs and cats, these worms have also been detected in ferrets, foxes, wolves, sea lions, and sometimes even in humans.

Life Cycle

The life cycle of a heartworm begins with the adult female releasing young microfilariae into the host animal's bloodstream. When mosquitoes bite the infected animal, they carry these microfilariae, which stay within the mosquitoes for the next 10 - 14 days, and mature into the larval stage. When these mosquitoes bite another animal, the larvae enter that animal's body, and take nearly six months to develop into mature adults. The adults release young heartworms, which circulate in the blood and constrict blood flow. Heartworms can live up to 6 - 7 years in the animal's body.


Since the number of heartworms in the animals tends to accumulate slowly over a period of months, the clinical symptoms of the infection may not be recognized in the initial stages. Especially dogs or cats exhibit no signs of the disease during the initial stages. Eventually they may show symptoms like:
  • Mild and persistent cough
  • Fatigue, or reluctance to move or exercise
  • Reduced appetite
  • Weight loss
  • Breathing difficulties
  • Vomiting, gagging, and even collapsing out of the blue
Prevention and Treatment

The American Heartworm Society recommends pet owners to take necessary preventive measures to protect their pets from this life-threatening disease. Since the disease is preventable, there are many options to do just that, such as daily tablets, chewables, monthly topical medication, and/or a six-month injection course. These medications disrupt the growth of the parasite before the adult worms reach the lungs and cause severe infection. When administered regularly on a timely schedule by a veterinarian and the pet owner, these medications are extremely effective, and can prevent the infection completely.

A chemical therapy can be used to eliminate heartworms. The worms are killed by injecting a drug called adulticide into the muscle during the series of treatments. As the treatment involves use of chemicals, hospitalization is usually recommended. If the infection reaches a non-curable or terminal stage, surgery is the best option. There are a variety of medications designed to destroy the microfilaria inside the animal's body. Though these medications may not provide 100% intervention, they should also been given under a veterinarian's supervision.

Therefore, if you observe any of the above mentioned symptoms in your pet, do not ignore them, and immediately take your pet to the veterinarian, as early diagnosis will save the animal from potential heart failure and death. You can also implement some preventive measures to maintain your pet's health, like keeping the sleeping area clean, using repellent sprays, or giving the prescribed preventive medications.