Feline Heartworm Disease

Heartworm disease is caused by a parasite named Dirofilaria immitis.

Heartworms are most commonly found in dogs, but now are known to also infect cats and other mammals.

The adult heartworms live in the heart and major arteries of the lungs where they interfere with the function of the heart and lungs.

The adult heartworm lives for 1-2 years.

Transmission Of Heartworms:

Heartworms can only be transmitted from one animal to another by mosquitoes.

Adult worms living in the heart produce offspring called “microfilaria,” which are found circulating in the blood of infected dogs.

A mosquito must then feed on the infected dog and ingest some blood containing these “baby heartworms” if the heartworms are to develop into the stage where they can infect another cat.

When the mosquito later feeds on another cat, the baby heartworms that have developed to the infective stage in the mosquito now escape from the mosquito into the second cat during the “blood meal” of the mosquito.

Once these infective larvae pass through the cat’s skin, they begin migrating through the tissues, eventually making their home in the heart and lungs where they mature into adult heartworms and start the cycle over again.

Heartworms can occur in cats kept totally indoors if an infected mosquito should enter the house.

Heartworms in cats is a serious disease! Whereas dogs can live with quite a few heartworms in the heart, because of their smaller size heart, 2-3 adult heartworms can be fatal to the cat.

Symptoms Of Heartworms In Cats:

Clinical signs of heartworm disease in cats are quite variable. Many cats do not show any signs of heartworm disease until they die.

In some acute cases, death may come so rapidly that there is insufficient time to make the diagnosis or provide any type of treatment. There are cases reported where the cat can appear clinically normal one hour before death.

However some cats will show such signs as vomiting, coughing, and difficult breathing.

Heartworm associated respiratory disease (HARD) refers to the damage caused by immature heartworms within the lungs of an infected cat. Asthma-like symptoms such as coughing and wheezing are common.

Coughing may be intermittent or occur in severe, sudden attacks that take place days apart.

Diagnosis Of Heartworms:

Clinical signs of heartworm are very similar to several other cat diseases. Therefore, diagnosis must involve ruling out other diseases which cause similar symptoms.

The diagnosis usually involves a combination of radiographs (x-rays) of your cat's chest, ultrasound examination of your cat's chest, and blood testing consisting of a basic blood screen, including a thyroid screen and specific tests for heartworms.

Treatment Of Heartworms:

Treatment of heartworms in cats is not nearly as successful as in dogs.

Treatment is complicated by the fact that after even one heartworm is killed in the heart; it can lead to an arterial blockage that has the potential to be fatal. Blood vessels in the cat are small enough to create serious risk while the dead heartworm is being removed from the body.

Another one of the major problems is that no clinical signs are observed in many cases until close to death.  Because of these complications, drugs which are used to kill heartworms successfully in dogs cannot be safely used in cats.

In some cases, surgical removal of the worms is recommended.  However, surgical removal of worms directly from the heart carries its own risks with it.

In many cases, the best "treatment" is leaving the heartworms alone, starting the cat on preventive medication so that it does not acquire additional heartworms, and attempting to control the symptoms of heartworm disease. Though this method carries risks as well, and sudden death is one of the "complications" encountered in cats with heartworm disease, this method often proves to be the safest method of treatment.

Prevention Of Heartworms In Cats:

Prevention of heartworm infestation is easily accomplished using products such as Heartguard Plus Feline, Revolution or Advantage Multi.  Your cat's veterinarian can help you determine which type of preventive medication is best suited to your cat's needs.