Most people think of heartworm disease as a problem that affects only dogs, but even though cats are more resistant hosts to heartworms, and they typically have fewer and smaller worms than dogs with a shorter lifespan, it is considered a more serious threat in cats and can lead to significant pulmonary damage and even sudden death.
What causes heartworm disease?
Heartworm disease is caused by a parasite that is carried by mosquitoes, and cats become infected when a mosquito bites into a cat for a blood meal and deposits heartworm larvae into the cat’s bloodstream. These larvae migrate and mature through several lifestages into adult worms. At about 3-4 months, they usually settle into the arteries and blood vessels of the cat’s lungs, where they continue to mature into adult worms for another 4-5 months. Worms do not have to develop into adults to cause symptoms.
Which cats can be affected?
While outdoor cats are more susceptible, even indoor cats can be affected (all it takes is one mosquito bite). Studies have shown infection rates as high as 10-14% in endemic areas.
What are the clinical signs of heartworm infection?
Symptoms can be non-specific and are often similar to those of other feline diseases. Affected cats may exhibit general signs of illness such as intermittent vomiting, lack of appetite, coughing, and asthma-like signs such as difficulty breathing or wheezing. Some cats may show acute symptoms, often related to the organs where the adult worms are thriving. Cats with an acute onset of symptoms may die quickly without allowing sufficient time for diagnosis or treatment.
How is heartworm disease diagnosed?
Heartworm disease in cats is much harder to diagnose than in dogs, once again proving the old adage that cats are not small dogs. Physical examination will often be non-specific. Further diagnostics may include x-rays, echocardiogram, and blood testing. Diagnostics have limitations, and sometimes, even a negative test cannot rule out infection.
How is heartworm disease treated?
Currently, there are no medications approved in the United States for treatment of feline heartworm disease. Cats who don’t show any clinical signs will often simply be monitored periodically and given time for a spontaneous cure. Monitoring through x-rays every 6-12 months may be all that is needed. If there is evidence of the disease in the lungs or blood vessels, treatment is generally focused on supportive care, sometimes using gradually decreasing doses of prednisone, a steroid. Cats with severe manifestation of infection may require additional supportive care such as intravenous fluids, oxygen therapy, antibiotics, cardiovascular drugs, and restricted activity through cage confinement.
Can heartworm disease be prevented?
Currently, there are four heartworm preventive products approved for use in cats: Heartguard for Cats (Merial), Revolution (Pfizer), and Advantage Multi for Cats (Bayer). Heartguard is taken orally, Revolution and Advantage are topical products. All of these products come with known side-effects, and deciding whether to use them for your cat will require an informed risk assessment in conjunction with your veterinarian. It is recommended that cats are tested for antibodies and antigens prior to beginning use of these preventatives. Never give heartworm or any other parasite prevention product for dogs to cats.
As with all parasites, it is believed that a healthy immune system makes cats more resistant to them. A healthy diet is key to a healthy immune system. Feeding a species-appropriate grain-free canned or raw diet may help prevent heartworms and other parasites.