Heartworm Infection in Cats
Written by Dr. Michael C. Fleck, DVM March 2009

Heartworms in CatsIt was just a few years back that heartworm infection in cats was essentially non-existent. For whatever reason, the feline population is no longer resistant to heartworm disease as it apparently was years before. The February issue of Clinicians Brief reported startling figures of the presence of heartworm in the cat population in many states. Antigen blood tests showed that the prevalence of heartworm infection in cats was as high as 33% in California, 20% in Florida and 12% in Michigan to mention a few.
Clinically the disease expresses itself in cats a bit differently than in dogs. In cats, lung disease is more prevalent and in dogs the heart appears to be more affected. To oversimplify, Pulmonary larval dirofilariasis or HARD occurs in cats that can ultimately lead to death. In addition to the respiratory problems in some affected cats, surprisingly most infected cats are asymptomatic or simply show no clinical signs at all -- they act and breathe normal. Unfortunately, the heartworm-infected cat can seem perfectly normal one day and be dead the next day.
Because mosquitoes transmit heartworm disease, inside and outside cats can be infected. Generally speaking, the larger the feral cat population in your neighborhood, the greater chance for your inside pet cat to be infected. What to do????
Heartworm blood testing in the veterinarian's office is not conclusive. Tests may show positive on less than 50% of the infected cats. Currently, the recommendation is to place all pet cats on heartworm preventative without blood testing for heartworm. Some veterinarians though do feel that testing annually or semi-annually, as is recommended for dogs, should be performed before dispensing monthly preventative medicine.
Monthly preventative medicine can be administered either orally (Iverhart, Heartgard, etc.) or topically (Advantage Multi, Revolution, etc.).
Let's not let heartworm disease get out of hand in the feline as it did in the canine. Please get your cat on heartworm preventative ASAP.

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