How Is Heartworm Disease Treated in Cats?

Heartworm disease is not just a dog disease. Cats get heartworms the same way that dogs do, through the bite of infected mosquitoes. Because cats have different physiology than dogs, however, heartworms affect them differently than their canine counterparts.  

In dogs, most infective heartworm larvae grow into adult worms, while the immune system of an infected cat kills off most heartworms in the early stages.  

However, these early infections can cause damage to the cat’s blood vessels in the lungs and the respiratory tract. This can result in a condition called heartworm-associated respiratory disease (HARD), leading to symptoms such as poor appetite, coughing, wheezing, and vomiting.  

Meanwhile, heartworms can also survive to the adult stage in cats and cause serious disease or death. In fact, without supportive care, approximately 20% of cats with adult worms can die, according to this study. 

Here’s another important fact: While infection with adult heartworms can be treated in dogs, there are no FDA-approved medications to kill adult worms in cats. The medication used to treat canine heartworm infection is not safe for cats. That means that heartworm prevention in cats is very important.  

Screening for heartworms in cats is done through blood tests. If the results show evidence of heartworm infection, your veterinarian may also choose to do X-rays, an ultrasound, and/or an echocardiogram. 

How Is Heartworm Disease Treated in Cats?

While cats with adult worms can’t be treated like dogs, there are steps veterinarians can take to increase the chances an infected cat will survive.  

• Supportive care. Veterinarians can prescribe a variety of medications to reduce the impact of heartworm infection. First, the cat should be placed on a heartworm preventive to stop more heartworms from developing. These preventives, along with the antibiotic doxycycline, should weaken the adult worm, eventually leading to its death. An antileukotriene can also be prescribed to reduce the chances of an acute respiratory distress syndrome occurring. Steroids should be prescribed to treat respiratory symptoms. 

• Monitoring. Cats with adult heartworms should be seen by a veterinarian at least every six months so the veterinarian can check the cat’s status and health. Cat parents should also keep a close eye on infected cats for sudden changes that can happen when the adultworms die inside the cat.  

• Emergency care. If your cat has been diagnosed with adult heartworms, you should be on the lookout for signs of a sudden reaction, which can occur when a heartworm (or worms) dies inside your cat. These signs include severe respiratory distress or even collapse, which need immediate veterinary care. Treatment may include IV fluids, bronchodilators, steroids, supplemental oxygen, and thermal support to help the cat through the crisis. In life-or-death cases, it is also possible to surgically remove adult heartworms. However, this procedure carries risks and should only be done by a veterinary surgeon who is trained in the procedure and knows the precise location of the heartworm(s).  

How Long Does Heartworm Disease Last in Cats?

When a cat is infected with heartworms, it takes six to seven months for the worms to grow to adulthood. As adults, they can grow to be 8 to 12 inches long and survive inside the cat for up to four years.  

However, the cat’s immune system gets rid of many worms at around two and a half to three months after infection, when the immature worms have moved to the pulmonary arteries (which take blood to the lungs).  

Can Cats Recover From Heartworm Disease?

Whether infected cats kill off heartworms in the early stages or have adult worms for several years, the damage to the cat’s respiratory tract is permanent. Some cats with HARD may have clinical signs such as an asthma-like cough or occasional vomiting, while other cats won’t show signs of disease.  

Cats with adult worms are more likely to get serious illness than cats that get rid of heartworms at the immature stage. If a cat is diagnosed with adult heartworms, careful veterinary monitoring and quick treatment of any respiratory crisis can improve their chances of survival and recovery. 

How To Prevent Heartworm Disease in Cats

The American Heartworm Society recommends year-round heartworm prevention for any cat living in the vicinity of mosquitoes and dogs or wild canids that may have heartworms. This includes indoor cats, who can be infected by mosquitoes that come indoors.  

Cat parents have multiple safe, effective, preventive products to choose from. Both monthly and every-other-month products are available, and options include oral and topical medications. Whichever product is used, giving heartworm preventive medications year-round is the safest and most effective way to protect cats from heartworm disease.  

Not only is year-round prevention easiest to remember (skipping doses can lead to cats becoming infected!), but heartworm preventives for cats also protect cats from other parasites, such as fleas, ticks, and intestinal worms. Cat parents should talk with their veterinarians to figure out which product is most helpful for their cat.