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Heartworm Awareness

Posted by Harry Shubin on

Heartworm Awareness

It’s summer (almost)… and the press is full of scares – Zika virus, Lyme Disease, West Nile virus… as if you didn’t have enough to worry about,  your cat would like you to hear about one more.  Fortunately – your cat also wants you to know that you can do something about this one!

You may know that heartworm is a serious illness that affects dogs, but did you know – it also affects cats, and is even more serious… because in cats, there’s no treatment?  Knowing just a few basics about heartworm may save your cat’s life.  There’s lots more information below, but knowing just these bullet points may make the difference between a long life and tragedy:

  • EVERY cat is susceptible to heartworm, even indoor cats – because the parasite is transmitted via a mosquito bite, and even with screens, and even if you never open windows, mosquitos may get inside on your clothing or when the door is opened.
  • The only effective way to avoid heartworm is to use a preventative – because once contracted there is no cure.
  • Certain flea preventatives - RevolutionTM and Interceptor® - also prevent heartworms (so they should be used even on indoor cats who have no contact with fleas!) and there is also a non-flea preventative called Heartgard® which is a chewable tablet (and cats seem to love it!)

Caused by Dirofilara immitis, heartworms are a potentially fatal parasitic worm living in the pulmonary arteries, lungs and hearts of cats. Heartworms are nematodes, a type of roundworm, they are several inches long, thin and white.  The disease is spread from mosquito to animals when the mosquito feeds from its host

While cats are more resistant to heartworm infestations than dogs, cats in particular are extremely vulnerable to heartworms if they do contract them,  and even a small number can lead to death.

In an infected animal, the adult heartworms produce their young, known as microfilaria, which swim around the bloodstream. Microfilaria require an intermediate host in the form of the mosquito. When the mosquito bites an infected animal, it takes up some of these microfilaria circulating in the animal's blood. Once inside the mosquito, they undergo further maturation, which takes 10 - 14 days, in which time they become infective larvae. When the mosquito feeds from a cat or dog, these infective larvae are injected into the animal.

Once in the cat, they take around 8 months to mature to adult worms. When they have matured they make their way to the heart (although other organs can also be infected with heartworms). Due to their resistance, cats are usually only infected with a small number of heartworms (usually between 1-3 worms), whereas in dogs numbers are generally higher. However, cats do not tolerate heartworm infection as well as dogs and even one or two heartworms can cause death.

Heartworms live in dogs for around 5-7 years and in cats for around 2-3 years. Cats are commonly found to have only one sex of heartworm, and it is unusual for cats to have microfilaria in their bloodstream. It is uncommon for heartworms in cats to produce microfilaria, due to the low number of worms found in cats.

Symptoms of heartworms are often non-specific in cats. Some symptoms include:

  • Coughing
  • Wheezing
  • Difficulty breathing
  • Heart murmur
  • Panting
  • Anorexia (loss of appetite)
  • Vomiting
  • Lethargy
  • Weight loss

But… some cats show no signs at all.

Diagnosis of heartworms in cats is often difficult and not always 100% reliable

There are no approved methods to treat heartworm in cats. The treatments which are available are themselves dangerous. A single dead worm can be fatal in cats as it can break away and cause a blockage of the pulmonary artery resulting in pulmonary embolism.

If there are no clinical symptoms your vet may decide not to treat the cat and wait for it to clear the parasite in around 2-3 years, monitoring the cat for signs of complications.

If the cat is displaying symptoms of heartworm disease supportive therapy may be recommended. Prednisone may be given to the cat to reduce the inflammation and reaction to the worm.

Cats with severe symptoms may require additional supportive therapy such as a bronchodilator to open the airways, oxygen therapy and intravenous fluids.

As you can see – prevention is the best option.  However, before using any products such as RevolutionTM or Heartgard®, your veterinarian should perform testing for heartworm.

Finally… you cannot catch heartworm directly from your cat, but it is possible to become infected via a mosquito bite.  Fortunately, heartworm infections in humans are extremely rare and almost all cases the larvae are unable to develop into adult heartworms.

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