Heartworm is something dog owners have been concerned about for years and with the influx of “Katrina Dogs,” southern Ontario has once again become a heartworm hot bed. As testing for heartworm improves, unfortunately new studies are undeniably showing that your cat's risk for a heartworm infection is as high as the family dog.
Feline heartworm is transmitted by an infected mosquito bite. Cats are susceptible to hearthworm disease even when kept indoors, as mosquitoes can find their way into the house. When the mosquito bites the cat to take its blood meal it introduces the heartworm larva into the cats bloodstream. These larval heatworms invade the blood vessels in the lungs. Although the parasite itself is the same, Heartworm disease in cats is very different from the disease in dogs. Cats have a stronger immune system so as a result they tend to have a lower worm population than dogs, the infections tend to be occult (non-reproductive) in nature, and the cats body may try to wall off larvae as cysts in other organs. This is why previously the traditional heartworm tests were showing heartworm positive cats as negative. As more sensitive testing has been developed we are now seeing the negative impact this disease has on our cats as well. Although the number of worms the cats get is lower, their heart is so much smaller that only 1 to 2 worms can cause serious injury. The damage by these parasites can be severe in cats and can easily cause sudden death.
The most common presentation of feline heartworm looks a lot like asthma, allergic bronchitis or other respiratory diseases. These diseases can all produce symptoms including difficult breathing, fast breathing, coughing, reduced activity, open mouth breathing and/or panting. Another common scenario is that the infected cat shows no signs at all initially although they may go on to show symptoms as damage to the heart muscle increases. The third presentation we see is a sudden death. This occurs when an infected cat has been able to compensate for the inflammation in the lungs, so signs do not become obvious until late-stage disease.
Unfortunately there is no medical cure or treatment specific for feline heartworm once a cat becomes infected. Cats are far more vulnerable to reactions with insecticidal products than dogs are. The available treatments that we use in dogs are toxic for your cat and a single dead heartworm can cause blockage in the pulmonary artery leading to death. If the cat does not show any clinical symptoms the safest option is to wait for the heartworm to die on it's own. A heartworm may live up to 2-3 years in a cat. During this time careful monitoring will be required and possibly supportive care. This all means if your cat becomes infected with heartworm, there is unlikely to be much active treatment that can be carried out to help your pet.
That’s all the bad news - The good new is feline heartworm is easy to prevent and many of our clients have unknowingly been doing so for several years!
Here at The Cat Clinic we have been using Advantage Multi and Revolution for our routine flea prevention and deworming protocols. They are both also licensed as a heartworm preventative for cats. Both topicals are applied once a month to the back of your cat's neck during the warmer months, providing waterproof protection from a number of parasites including heartworm. If you haven't gotten your box of Advantage Multi or Revolution for this summer season please contact the clinic to arrange for this very important protection for your feline family member.
Written by Angelina Johnstone RVT