A multimillion dollar advertising campaign has probably made you aware of a new product to prevent heartworm disease in cats. Heartgard™ for Cats is a palatable, safe, monthly medication. The big question is whether or not cats in this area are at risk of getting heartworms.

Heartworms are transmitted from animal to animal by mosquitos. Cats are not the natural host (dogs are) for heartworms with the incidence being about 10% of the incidence rate in dogs for a given geographic region. The Heska Company which developed the antibody test had run 1724 tests in Virginia through November 30,1997. Of these, 244 (or 14.55%) were positive. This is similar to or exceeds the rate of Feline Leukemia and Feline Immunodeficiency Virus infections. An analysis of heartworm positive cats at North Carolina State University School of Veterinary Medicine in Raleigh, NC, revealed that 1/3 of the cats were housed solely indoors!

The absence of a sensitive test to detect the heartworm parasite has hindered our knowledge regarding the prevalence of infection in cats. The existing test used in dogs requires the presence of 3-6 female worms to detect the infection. Due to the small size of the feline heart, more than 3 worms will probably cause sudden death. Recently, an antibody test became available that can detect heartworm exposure in the cat. With the introduction of this test, our ability to determine the prevalence of heartworm disease among the cats in our practice area will be greatly enhanced.

There is no safe, reliable treatment once a cat is diagnosed. Fortunately, the adult worm only lives 1-3 years versus 5-7 years in the dog. The current goal of treatment is to prevent further infection and to manage clinical signs. The most common clinical signs are chronic vomiting and coughing. Sudden death accounts for 1/3 of the diagnosed cases in the veterinary literature. We now recommend heartworm antibody testing of all unexplained chronic vomiting and coughing.

Dr. Ray Dillon of the School of Veterinary Medicine at Auburn University, a well known and respected authority on heartworm disease, feels that the most serious complication of heartworm infection in the cat is inflammatory lung disease. This is caused by the migration of the worm larvae through the lung tissue and the subsequent death of the adult worms. There is evidence that this inflammation does not resolve with the elimination of the infection. This may predispose the cat to bronchial asthma which is being diagnosed with increasing frequency. Based on the percentage of antibody positive cats in Virginia and the safety and effectiveness of preventative treatment, Kingstowne Cat Clinic currently recommends Heartgard™ for Cats in this area. Certainly cats that travel or move to heartworm endemic areas should be on preventative medication. We must work together as a team to determine the risk factor for each individual cat and the peace of mind afforded by a preventative regimen.

Update 1: In January 1998, we participated in a clinical study with the veterinary schools at Texas A&M and North Carolina State University and sponsored by Merial who manufactures Heartgard™ for Cats. The goal of the study was to determine the incidence of heartworm infection in the general healthy cat population. To participate, the cat must have lived in the area for the past three years, and the owner had to answer a few questions. Of the forty samples we submitted, 15% were positive and 30% of those were totally indoor cats. In 1998, 20 of 111 (18%) tested in our practice tested positive. Many of these presented with signs of asthma.

Update2: Revolution is a new once a month topical medication to prevent heartworm infection. It also kills fleas, earmites, and intestinal parasites.