Heartworms, as the name implies, are actual worms that live in the heart.  Our pet dogs and cats are susceptible to heart worm infections. This is a preventable disease.  First we will discuss the lifecycle of the heartworm.

The adult heartworm produces "babies" or microfilaria.  These tiny microscopic parasites are in the blood stream of the infected animal 5-6 months after being infected.  These are the L1 stage of the heartworm.  When a mosquito takes a blood meal from an infected animal, the L1 changes into the L3 lifestage of the heartworm in the body of the  mosquito.  This L3 is the infective stage. The L3 is injected into the next animal when the mosquito takes another blood meal. Then this L3 begins to mature in the heart of the dog or cat into the adult worm.

This said, you can see that taking a blood sample from an animal with heartworms and injecting it into another will not cause heartworms to develop in the second animal. It is only in the mosquito that the L1 developes into the L3 stage.

While both dogs and cats can get heartworms, this disease is slightly different in each species.  Dogs can get HUNDREDS of adult worms in their heart.  These cause a physical damage to the heart as well as a disruption of heart function and heart flow.  Cats usually get from 1-5 adult worms in their heart.  So, you are thinking that cats don't seem to have as much of a problem.  Actually, heartworms in a cat are much worse than in the dog.  The adult heartworm releases a substance that causes damage to the lungs.  A dead heartworm in the cat can cause an  anaphylactic-type reaction. (Big time allergic reaction that is potentially fatal).

Treatment is available for dogs with heartworms.  But by the time the heartworms are diagnosed there is already damage to the heart itself as well as other organs of the body.  Treatment of cats is dangerous since the dead worms are the cause of the allergic reaction. So, prevention is the name of the game.

The goal of heartworm prevention is not to stop the mosquito from biting your pet, but to stop the L3 from further developing into the adult worm in the heart.  There are many types of prevention on the market.  There are tablets that can be given once a month.  Some of these tablets also prevent the common intestinal worms,  hook and round.  Some help with flea control.  There is also a topical preventative (applied to the skin) once a month.  And for those who have trouble remembering a monthly treatment there is a shot that is given every 6 months to dogs.

Please discuss with your veterinarian the right preventative for you and your pet.

While we think of mosquitoes as being a summer problem, studies in the South have shown that there may be a 4-6 week window in January or February when mosquitoes are not on the scene.  The bottom line:  Heartworm prevention should be practiced all year round!

Dr. Caroline Montgomery

Metro Cat Clinic