Conscientious pet owners understand they must be on the lookout for a host of issues that can affect the health and well-being of their pets. One such issue is heartworm.

What is heartworm?

The American Heartworm Society notes that heartworm is a disease caused by foot-long worms that live in the heart, lungs and associated blood vessels of affected pets.

Known as heartworms, these worms can cause severe lung disease, heart failure and organ damage. Some instances of heartworm may even prove fatal.

Who gets heartworm?

Heartworm disease affects dogs, cats and ferrets. Heartworms also live in wolves, coyotes, foxes, and sea lions. And while such instances are rare, heartworms have even been found in humans.

How is heartworm transmitted among pets?

Mosquitoes transmit many diseases, and they even play a role in the transmission of heartworm. The AHS notes that adult female heartworms living in infected dogs, foxes, coyotes, or wolves produce microfilaria, which are microscopic baby worms that circulate in the animals’ bloodstreams.

When mosquitoes feed on the blood of these infected animals, they pick up microfilaria. Within 10 to 14 days, these microfilaria mature and develop into infective stage larvae.

When mosquitoes then bite another animal, these larvae are deposited onto the surface of the skin of those animals, ultimately entering their new hosts through the wound created by the mosquito’s bite. The larvae then spend the next six months maturing into adult heartworms.

How long do heartworms live?

Upon reaching maturity, heatworms can live for five to seven years in dogs and for two to three years in cats. According to, heartworm in ferrets can be rapidly progressive and fatal.

What are the symptoms of heartworm?

Heartworm symptoms can vary depending on the type of animal that is infected. Dogs infected with heartworm may exhibit few or no symptoms in the early stages of the disease, only gradually exhibiting symptoms as the infection persists. Such symptoms include mild persistent cough, reluctance to exercise, fatigue after moderate activity, decreased appetite, and weight loss.

As heartworm progresses, dogs infected with the disease may develop swollen bellies due to excess fluid in their abdomens. Dogs infected with large numbers of heartworms may develop sudden blockages in their heart, which can lead to cardiovascular collapse, threatening the dog’s life.

Cats may exhibit subtle or dramatic symptoms of heartworm. Coughing, asthma-like attacks, periodic vomiting, loss of appetite, and weight loss are some of the more subtle symptoms of heartworm in cats. But some cats may struggle to walk, experience fainting spells or have seizures as a result of heartworm. The AHS notes that the first sign of heartworm in cats is sometimes sudden collapse or sudden death.

Ferrets with heartworms may seem tired all the time and exhibit shortness of breath even after just a few minutes of activity. Ferrets may also experience fluid buildup in their abdomens due to heart failure and blocked blood vessels.

Can pet owners protect their pets from heartworm?

The AHA recommends that pet owners get their pets tested for heartworm every 12 months. In addition, the AHS advises pet owners to give their pet heartworm preventive 12 months a year.

More information about heartworm is available at

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