Prevalence of exposure to Dirofilaria immitis in cats in multiple areas of the United States.

169 n BACKGROUND The prevalence of feline heartworm disease (FHD) in the United States is largely unknown, due, in part, to a previous lack of interest and understanding of heartworm infection in cats and limitations in current diagnostic methodology. Currently available antigen tests for detection of Dirofilaria immitis infections are less sensitive in the cat due to more frequent all-male infections (low worm burdens) and because immature worms not routinely detected by antigen tests can be pathogenic in cats. Echocardiography allows visualization and detection of worms located only in the heart or the base of the pulmonary artery. Necropsy may not yield definitive diagnosis due to the ability of worms to drift to the periphery of the pulmonary arterial tree, increased frequency of aberrant migration, and the transient nature of the disease in the cat. Antibody tests have been developed that detect the cat’s response to the presence of third and fourth larval and the fifth adult stages of D. immitis. The recent interest in FHD has resulted in a number of studies of the prevalence in symptomatic and asymptomatic cats. In 1992, Guerrero and colleagues presented a review of the prevalence of D. immitis infections in dogs and cats in the United States that varied from 0% to 19%. Later Ryan reported that the necropsy prevalence in cats from shelters in the southeastern and eastern areas of the United States ranged from 0% to 16%. Atkins and colleagues demonstrated an infection rate of 9% and an exposure rate (based on antibody positivity) of 26% in 100 cats presented for cardiorespiratory abnormalities in North Carolina and Texas. Robertson-Plouch and colleagues found 44% of 215 symptomatic cats to be antibody positive in Texas, Florida, Tennessee, and South Carolina. While important, these studies have not addressed the prevalence of heartworm infection in the general population of pet cats presented for routine care. In addition, most previous studies have centered on areas in which heartworm disease is known to be endemic in dogs and Prevalence of Exposure to Dirofilaria immitis in Cats in Multiple Areas of the United States