Heartworm in Cats

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(Above picture courtesy of Shutterstock.com)

If you think cats are safe from heartworm disease, think again.

Unlike their canine counterparts, cats aren’t typical hosts for heartworms, and while most worms in infected cats don’t reach the adult stage, immature worms can still cause a condition known as HARD (heartworm associated respiratory disease). More importantly, however, infected cats remain undiagnosed longer than infected dogs, while Melarsomine, the drug of choice prescribed to kill adult heartworms in dogs, is toxic for cats.

The miniscule mosquito plays a MAJOR role in the life cycle of the heartworm. Adult heartworms living in infected wildlife animals like foxes, coyotes or wolves produce microscopic baby worms called microfilaria which circulate in their bloodstream. When a mosquito bites an infected animal, it picks up these baby worms which mature into larvae within 10 to 14 days. When the infected mosquito bites a cat, the infective larvae are deposited onto the surface of her skin and enter her body through the wound. It takes approximately 6 months for the larvae to mature into adult heartworms which can live for up to 2 or 3 years inside her.

A serious and progressive disease, the earlier it is detected, the better the chances your cat will recover. Signs of heartworm disease range from very subtle to very dramatic. Symptoms can include coughing, asthma-like attacks, periodic vomiting, loss of appetite, or weight loss. Sometimes an infected cat may have difficulty walking, faint, have seizures, or suffer from fluid accumulation in her abdomen. Sadly, in some cases, the first sign of the disease is her sudden collapse or sudden death.

Heartworm disease is now found throughout the country, risk factors are impossible to predict, and since infected mosquitoes can come inside, both outdoor and indoor cats are at risk. Because of this, the American Heartworm Society suggests your cat be tested by your vet every year and given a heartworm preventive all year round.

Your vet will perform a thorough physical examination of your cat, run blood tests, take x-rays, and in some cases, order an ultrasound. If her diagnosis is positive, and with no approved drug therapy available for cats, she can often be helped with good veterinary care and a long-term management plan. Many cats even experience a spontaneous clearing of the heartworms.

If she’s not exhibiting any signs of respiratory distress, but worms have been detected in her lungs, your vet may recommend she have chest x-rays every 6 to 12 months. If she’s showing some mild symptoms, corticosteroids such as prednisone or prednisolone will most likely be used because of their potent anti-inflammatory properties, with treatment often continuing until the adult worms have died and are cleared from the lungs — a two to three year process.

If the disease is severe, your vet may recommend your cat be hospitalized in order to provide her with such therapy as intravenous fluids, drugs to treat her lung and heart symptoms and antibiotics coupled with general nursing care. In some cases, surgical removal of the heartworms may be possible.

Like healthy cats, any cat with heartworm disease should be given preventives to keep new infections from developing if an infected mosquito bites her again. Whether the preventive you choose is a pill, a spot-on topical medication or an injection, all three work by eliminating the infective larvae and keeping them from maturing into adult worms. For this reason, the preventives must be assiduously administered on schedule — monthly for pills and topical medications, and every 6 months for injections.