Think heartworm disease only occurs in dogs? Think again. Recent studies show that heartworms in cats exceed the rate of feline leukaemia virus (FeLV) infection and feline immunodeficiency virus (FIV) infection in some parts of the United States.
No recent studies have been done in Australian cats, but the infection rate is directly related to the number of heartworm infected dogs in any given area.
The good news is that you can protect your cat from this nasty disease with a simple monthly spot-on treatment.
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About the heartworm parasite
Heartworms in cats are caused by the parasite Dirofilaria immitis, which naturally infects dogs. Adult worms live in the heart and produce offspring called microfilariae. These circulate in the bloodstream of infected animals and are picked up by mosquitoes when they feed.
Inside the mosquito, they develop into infective larvae. When that mosquito bites again these larvae are transferred to a new host – your cat. Over 3 to 4 months, the larvae develop into immature worms and migrate through the bloodstream to the lungs and the heart where they mature and produce more offspring, starting the cycle over again.
How do cats get heartworms?
Cats get heartworms the same way dogs do – through the bite of an infected mosquito. It only takes one bite to transmit the disease, which means even indoor cats are at risk.
Heartworms in cats versus dogs
Because cats aren’t the parasite’s natural host, they develop a very strong immune response against juvenile worms. Generally, it is this overactive immune response that causes the symptoms of heartworm disease in cats, rather than the adult worms in the heart themselves.
In dogs, heartworm disease mainly affects the heart. In cats, it’s a lung disease since that is where juvenile worms are present. That’s why in cats, the disease is better known as Heartworm Associated Respiratory Disease (HARD).
The strong immune response results in inflammation of the lungs, and can lead to serious respiratory problems. Common heartworm symptoms in cats include:
- lethargy and weakness
- loss of appetite and weight loss
- coughing
- vomiting
- difficulty breathing
- fainting
- or in the worst case, sudden death.
These symptoms are not unique to heartworm infection, so cat heartworm disease (HARD) can often be misdiagnosed as feline asthma.
If heartworms survive to adulthood in cats, they usually only live for 2 to 3 years compared to 5 years on average in dogs. When these worms eventually die, their decaying bodies can break apart and pieces can lodge in blood vessels, forming clots that trigger widespread inflammation. This can cause complications in many vital organs including the lungs, kidneys and the brain. Because the death of adult worms can cause such dangerous reactions, veterinarians generally avoid treatments that kill the worms directly. In fact, about one in three treated cats can suffer life-threatening complications when the worms die.
Diagnosing heartworms in cats
Diagnosing heartworms in cats is more complicated than it is in dogs. The standard blood tests detect proteins produced by adult female worms. Worms often don’t survive to adulthood in cats and if they do, the number of worms is much fewer than in dogs, so this blood test can be negative even in an infected cat. And if a cat is only infected with male worms, they will not be detected by this test.
Another type of blood test looks for antibodies that the cat’s immune system produces in response to heartworm infection. This test can be helpful, but it’s not always definitive. A positive result doesn’t necessarily mean there’s an active infection, because antibodies can remain in the bloodstream for years after the infection has cleared. On the other hand, if the infection is still in its early stages, the test might come back negative since it takes time for the body to produce detectable levels of antibodies
Current recommendations for diagnosis of heartworms in cats is based on a combination of clinical signs, antigen testing and if this is negative, antibody testing and imaging such as chest X-rays or heart ultrasound.
Cat heartworm treatment and prevention
Unfortunately, there’s no safe cure for heartworm infection in cats. Because of the risks involved in killing adult worms, vets focus on managing symptoms. Cortisone or other anti-inflammatory medications may be prescribed to calm the immune response, and the cat’s lung condition is monitored with X-rays every six months.
Monthly spot-on or oral preventatives kill larvae before they reach the heart or lungs. All cats –indoors and out – should stay on heartworm prevention year-round, as it only takes one mosquito bite to cause infection.
Final thoughts
Heartworm disease may be better known in dogs, but cats are far from immune. Even one mosquito bite can put your cat at risk – and because the signs are often mistaken for asthma or other breathing problems, prevention truly is the best medicine. With regular monthly treatments, you can protect your cat from this dangerous parasite and the stress of potential illness. It’s a simple step that can make a world of difference – so make sure your cat’s heartworm prevention is up to date.
Keeping cats safe from heartworm doesn’t have to be complicated. If you’ve got a question about prevention or want to share what you use for your cat, join the conversation below.
I was totally unaware that cats can also become victim of heart worm disease. But this article is the eye opener for me with a quality information.
This is SO important – especially in the midwest. We feared Allie might have become infected 3 years ago, which is when we learned it’s more prevalent in our area in CATS than it is in DOGS, mainly because the news still hasn’t been heard by all that cats can get heartworms too.