What Pet Owners Need to Know About Heartworm Disease

February 29, 2016

heartworm aikoBy Linda Cole

Unlike ticks and fleas that can be seen on pets, heartworm disease quietly infects an unprotected dog or cat without any warning. There are, however, some symptoms of heartworm disease that pet owners should be aware of. Also, it’s important to note that this disease affects cats differently than dogs.

Dirofilaria immitis, commonly known as heartworms, are essentially foot-long parasitic roundworms that live in the lungs, heart and surrounding arteries of infected pets. Left untreated, the disease can damage organs in the body, cause severe lung disease, heart failure and eventually death. Heartworms can be treated, and how severe the infestation is depends on the number of worms in the body, how long the pet has been infected, and how he responds to the disease. However, curing heartworms can be difficult, it takes time to recover, and treatment is risky and expensive.

Heartworm disease is rarely found in humans. Common heartworm hosts include dogs, cats, ferrets, wolves, coyotes, foxes and sea lions. Once inside a host, the parasites mature into adults, mating and reproducing which increases the number of worms in the body. Some dogs have been found with hundreds of worms. An affected dog can suffer long lasting damage to the heart, arteries and lungs that affects their overall health and quality of life even after the worms are eradicated.

Whereas dogs are a natural host for heartworms which allows the parasites to complete their life cycle, cats are atypical (not typical) hosts and most worms never survive to Dog-Animated-no-offerreach adulthood. Felines infected with the worms generally only have one to three adults and many cats can be infested with worms that never mature. However, even immature worms can cause serious health issues.

Because the disease affects cats differently, it’s harder to diagnose and can often go undetected. Felines can suffer from a condition called heartworm associated respiratory disease, or HARD for short. Unfortunately, there is no medication available to treat heartworm disease in cats. The treatment used for dogs cannot be used in cats. The only way you can protect your kitty from heartworms is by using preventive protection to reduce her chances of being infected. Year-round prevention is recommended for both dogs and cats.

Heartworms are transmitted by infected mosquitoes and have been reported in all 50 states and around the world. When the adult female worm living in a host reproduces, microscopic babies (microflaria) circulate throughout the bloodstream of the host. A biting mosquito picks up microflaria when it takes a blood meal. Once inside the insect, it develops into what’s called infective stage larvae in 10 to 14 days. Larvae is left on the surface of the skin when the mosquito bites a dog or cat and it enters into the body through the bite wound. It takes around six months to mature into adult worms once inside the body of the infected animal. These worms can live inside dogs for five to seven years, and two to three years in cats, all the while continuing to reproduce.


The symptoms of heartworms in dogs include a persistent mild cough that gets worse as the disease progresses, reluctance to exercise, fatigue after going on a short walk or doing other moderate exercise, decreased appetite and weight loss. A swollen abdomen is a serious sign of excess fluid in the abdomen and your pet is at risk of developing heart failure. Severe infestation can cause cardiovascular collapse from a sudden blockage of blood flow in the heart. Symptoms are labored breathing, pale gums, coffee-colored or dark bloody urine. At this point it’s imperative to get your pet to the vet immediately.
heartworm tess
Heartworm disease affects cats in more subtle ways. The first sign your kitty is infected may be, in some cases, sudden collapse or death. In fact, it’s easy to misdiagnose heartworms in cat as asthma. Sometimes the disease can cause a cat to have difficulty walking, seizures, fainting spells, or have a swollen abdomen. Other symptoms can include asthma-like attacks, coughing, periods of vomiting, loss of appetite and weight loss. Anytime your cat isn’t eating like she should, that’s cause for concern. Going just a couple of days without eating can put a cat at risk of developing fatty liver disease which can be fatal if left untreated. Because mosquitoes can get inside your home, indoor only cats can also be infected.

A pregnant mother can’t pass heartworms to her unborn babies or through her milk during nursing. The only way a dog or cat can get heartworm disease is from the direct bite of an infected mosquito. One of the best ways to keep mosquitoes away from your yard is to make sure there’s no standing water. In most cases, mosquitoes only travel 1,000 feet from their breeding site, which is in stagnant water in bird baths, pet water bowls, puddles, gutters, or anything that holds or traps water.

Top photo by Aiko Vanhulsen/Flickr
Bottom photo by tess/Flickr

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