Incidence of Heartworms in Cats

Heartworms, a type of nematode called Dirofilaria immitis, are thin parasitic worms that infect a cat's heart, lungs and arteries, sometimes causing sudden death. Although more common in dogs -- who are the natural host of the parasites -- than cats, heartworms can infect a cat. Once infected, heartworms can cause severe inflammatory and immune responses in the cat, according to the American Society for the Prevention of Cruelty to Animals.

  1. Transmission and Lifecycle

    • A cat acquires heartworms when bitten by an infected mosquito, who deposits heartworm larvae into the cat's blood. Once bitten, the heartworms mature for about six months, before infesting the right side of the cat's heart, pulmonary arteries and blood vessels of the lungs, according to Pawprints &Purrs. The heartworms, usually around one to three, then reproduce, creating immature heartworms, called microfilaria, which live in the cat's bloodstream. A cat or dog cannot transmit the disease directly to another cat; instead, an infected animal is bitten by a mosquito, who acts as an intermediate host for 10 to 14 days and then transmits the larvae into another animal by biting it.

    Symptoms

    • Worms arrive in the heart and lungs during the initial stage of infection, known as heartworm-associated respiratory disease. Early signs of a heart worm infection resemble those of asthma or bronchitis, including coughing, difficulty breathing, weight loss, convulsions and lethargy. Other signs of infection include vomiting, collapse, blindness or convulsions. Some infected cats show no clinical symptoms of a heartworm infection and suffer from sudden death due to a worm entering the pulmonary arteries and stopping the flow of blood to the lungs.

    Diagnosis and Treatment

    • A cat with a heartworm infection needs treatment by a veterinarian, who will first perform a series of tests to diagnose the condition. Blood tests may show the presence of antibodies to the worms, microfilaria or antigens produced by female worms, indicating an infection. Other tests include an echocardiogram and radiographs of the heart and lungs. Unfortunately, once diagnosed, no approved treatments exist to treat heartworms in cats. Since the heartworms usually live for two to three years, most veterinarians will simply manage the symptoms of the disease until the worms die naturally. Cortecosteriods can relieve the inflammation in the lungs caused by the worms, diuretics treat fluid in the lungs and oxygen eases breathing difficulties to stabilize the cat. If necessary, a veterinarian will treat the cat with a drug called Caparsolate, to kill the heartworms, but this can lead to acute pulmonary failure and death.

    Prevention

    • Because of the lack of treatment options, you need to take steps to prevent your cat from becoming infected with the worms. Keep your cat indoors to prevent exposure to mosquitoes, especially in areas where these insects are most common. Give or apply a heartworm preventative treatment to your cat, which prevents the worms from maturing and multiplying such as Revolution, Advantage Multi, Interceptor or Cat Heartgard chewables, according to Vetinfo. Before using these medications, have your cat tested for heartworms. Only use the medications on kittens older than eight weeks. Never use products designed for dogs on cats, as they can cause toxicity.