Mosquito season is almost here. Can your indoor cat – the one that never goes out – be at risk for heartworm disease? Heartworm disease is a parasitic disease that involves a long thin worm that lives in the blood vessels and heart of infected pets. It is transmitted by mosquitoes and can infect both dogs and cats.

Cats that are indoors may actually be at higher risk than cats that go out. In fact, up to 33 percent of reported cases are in cats who are described by their owners as "strictly indoors." Males are a bit more likely than females to be affected. Age is not a risk factor; cats of any age can be affected, with cats as young as 1 and as old as 17 having been diagnosed.

Heartworms are present (endemic) in most parts of the United States and in many parts of North America. Mosquitoes are the key – without them the disease cannot spread. The highest rate of infections is found in subtropical climates like those of the southeastern United States, the Gulf States, and Hawaii.

However, heartworms are also found throughout the central and eastern United States, particularly near oceans, lakes and rivers. When compared to dogs, cats are naturally resistant to heartworms (estimated at about one-fifth as likely to become seriously infected as dogs in the same region); however, heartworm disease in cats is often more severe than in dogs.

Prevention

Prevention of heartworm disease is simple. "Preventatives" kill microscopic larvae that are left behind by mosquitoes when they bite a cat. In most cases, a once-monthly pill (Interceptor® brand of milbemycin for cats or Heartgard® brand of ivermectin for cats) is effective in preventing heartworms from taking hold. A recently available preventative for heartworms, Revolution® brand of selamectin, is applied to the skin once monthly. Revolution can also control fleas. Both Heartgard® for cats and Revolution® also help to prevent intestinal parasites.

Recommendations

Owners of all cats living in areas endemic for heartworms should discuss the pros and cons of preventative care with their veterinarian. If dogs in the area receive heartworm prevention, it is likely that cats also may benefit from this protection. Interceptor® for cats, Heartgard® for cats and Revolution® for cats are safe and effective products. Do NOT use your canine heartworm medicine in your cat. The drug dosing is very different between species. Speak to your veterinarian about the need for preventative therapy, administration guidelines and when to start and stop prevention treatments.

Heartworm disease in cats can have a wide range of symptoms, with some cats being completely asymptomatic (no symptoms at all). Others may show vague, generalized clinical symptoms. A small percentage, however, may show severe life threatening symptoms.