Feline Heartworm Disease

What is feline heartworm disease?

Feline heartworm disease can develop when a cat is bitten by a mosquito carrying microscopic heartworm larvae of a parasite called Dirofilaria immitis. While the mosquito is feeding on the cat, these larvae are deposited onto the cat’s skin and can migrate into the cat’s body. Eventually these larvae make their way into the feline’s bloodstream. In felines, this process leads to a condition called Heartworm Associated Respiratory Disease (H.A.R.D.), in which heartworms develop and live in the pulmonary arteries and the right side of the heart. This can lead to severe lung disease and sudden death. Unlike in canines where large numbers of worms develop, in cats only a few worms reach maturity, but unfortunately in cats even a single heartworm can have devastating and fatal consequences.

Heartworm disease was once believed to be a condition only affecting dogs, foxes, wolves, and coyotes. However, according to the American Heartworm Society recent studies have indicated that feline heartworm infection in cats is becoming more common, even in indoor cats. Studies have shown that feline heartworm infection rates are likely to meet and surpass infection rates for feline leukemia. Any cat exposed to mosquitos is susceptible to heartworm disease, and since mosquitos often find themselves inside of people’s homes both outdoor and indoor cats are at risk. Studies have also shown that an astounding 27% of the positive cases of feline heartworm disease have occurred with cats labeled as “strictly indoors.” Outside cats are more likely to be exposed to steadily increasing levels of larval heartworms. Mosquitos are very good at getting into your home, and staying there until killed; indoor cats are then exposed to being bitten day and night with less protective antibodies present to fight off the heartworm larvae. The smaller the size of cat in relation to the number of parasites can result in a life-threatening situation.

Signs of Heartworm Associated Respiratory Disease in Cats

Oftentimes, signs of feline H.A.R.D. can mimic common cat symptoms like asthma, pneumonia, vomiting, ie. hairballs. Symptoms can appear to be mild and subtle, or severe and life threatening; these may be loss of appetite, sluggishness, intermittent vomiting (not associated with eating), coughing, wheezing, and respiratory distress.

The arrival and development of immature heartworms in the blood vessels of the lungs may lead to lethargy, anorexia, vomiting, and respiratory disease. These symptoms may occur as early as three to four months after infection while the worms are still very small. Even if all worms die before becoming mature adults, respiratory symptoms may develop, such as permanent inflammation in their lungs, and continue for the remainder of the cat’s life. Worms may continue to develop to adult stages and earlier symptoms may persist. However, some infected cats will show no symptoms, might appear clinically normal, and die suddenly with no evidence of preexisting illness. As adult worms eventually die, cats will often have violent reactions to the dead worms, (pieces of dead worms can break off and clog blood vessels, cutting off blood flow to important tissues or organs) causing extremely rapid signs of respiratory distress that can lead to sudden death.

Detecting Heartworm Infection

There are currently two different blood tests, called Antigen and Antibody, available to assist veterinarians in diagnosing heartworm disease in feline pets. We can test your cat for heartworm disease right in our clinic.  Unfortunately, test results do not always produce clear answers, even with professional interpretations. Positive Antibody tests indicate heartworms were present at one time, but do not necessarily mean that the cat is still infected. Antigen tests cannot diagnose: very early infections, infections caused by only one or two worms, or infections consisting of an all-male worm population. Therefore negative test results are not always accurate either. Confirming a diagnosis can be difficult; multiple blood tests along with chest X-rays and ultrasound imaging of the heart and lungs are often needed to make the diagnosis. 

Treatment and Prevention

Although feline heartworm disease is easy to prevent, it continues to be a potential major health problem in the lower forty-eight states as there is no medicinal cure for the disease. Heartworm Antigen testing is recommended to screen for heartworm disease in cats although as previously stated, it is possible to receive a false negative result. The best treatment is routine use of heartworm preventatives for your feline. Various heartworm preventatives are available for your feline pet, but they all work by killing heartworm larvae acquired during the previous month—they do NOT protect cats from future infections. Annual testing may be recommended for felines to monitor the success of your heartworm prevention regime as instructed by your veterinarian.

Please feel free to call the doctors at Country Veterinary Clinic at (231) 843-3213 if you have any further questions.