Dirofilaria immitis is the medical term for the infection we all recognize as heartworm. The first cases of feline heartworm were reported in Brazil in 1921, since then it has been reported around the world. It is interesting to note that feline heartworm is reported more frequently in areas where dogs with heartworm are reported as well. However the number of reported feline cases remains lower than canine cases in these high-risk areas. Furthermore, the male cat is more susceptible to this disease than the female. Also the presenting symptoms and diagnostic approaches are different in dogs and cats reported to have contracted this disease.

Heartworm is passed on to cats by infected mosquitoes that carry the L3 Larvae. When the larvae mature and become adults they develop into worms and these parasites attach to their host and live within the body. The reason this parasite, a type of roundworm, is known as a heartworm is that in the final stages of the disease they have travelled up to the heart, where they can live for years and eventually cause congestive heart failure in your cat.

Heartworms go through several stages of development. In cats the mosquito L3 Larvae (third stage) does not restrict itself to a specific location (the way it would happen for dogs) but the larvae can appear in the brain, abdomen or third layer of the skin. It is only during the final stage of the infection that the heartworm has reached the cat's heart.

Infected cats do not infect other cats. What that means is that in order for a cat to be bitten by an infected mosquito that mosquito must have first bitten a dog or other species of animal then after a certain period of time bite the cat. There are some mosquitoes that will only feed on dogs, and some that will feed on either.

Once introduced into the cat's system, the heartworm can live up to two years as compared to the dog where it will live up to five years. Because of this, the cat actually has a better chance of recovery from heartworm infection.

Symptoms

Coughing and respiratory complications - It takes about 100 days after the initial bite for the worm to reach the lungs. The arteries in the lungs become inflamed and the cat's auto immune system cannot destroy the worm. The feline will cough as a result of the inflammation. Since the lungs are not receiving sufficient oxygenation because of the impaired arteries, the cat will become out of breath quite easily (during exercise, playing and romping around).

Bleeding occurs when there is blood clotting due to the infection present in the lungs.

Vomiting

Pulmonary Eosinophilic Granulomatosis - which is a type of pneumonia that occurs due to the flooding of inflamed cells that these worms, brings about in the lungs.

Heart Failure

PULMONARY HYPERTENSION is a condition that occurs when the arteries are filled with heartworms, the blood flow is obstructed and the heart must pump even harder to push it through.

Heart ARRHYTHMIA happens when worms fill the heart and the pumping action is compromised. The heart wall thickens due to the added stress and the pumping rhythm is disrupted. The heart is forced to work harder and sudden death can occur once the heart becomes too taxed.

Diagnosis

Testing for the presence of antigens and antibodies by blood test.

Treatment

Adulticide therapy (killing the heartworms with chemicals such as arsenic) is used for dogs, it is less effective for cats but might be necessary if the cat is in the advance stages of the disease.

Electrocardiogram, radiography, echocardiogram

Surgery has shown some success for the removal the worms found in the right heart ventricle and arteries of the lung.

If the cat is not showing any symptoms the veterinarian may elect to simply monitor the feline with radiograph imaging until the disease runs its course.

Preventative treatment is always the best course of action. There are several products on the market such as Heartguard30, Revolution and Interceptol, which can be purchased through your veterinarian. Make sure that your cat gets its annual treatment.