Filarial Worm Infections in Shelter Dogs and Cats from Northwestern South Carolina, U.S.A

Abstract

During 1991–1992 and 1999–2000, domestic dogs (n = 611) and cats (n = 71) from animal shelters in Anderson, Pickens, and Oconee counties in northwestern South Carolina, U.S.A., were examined for the filarial heartworm, Dirofilaria immitis. For both dogs and cats, whole blood was collected and tested for microfilaria using the Modified Knott's technique. In an effort to find adult heartworms in cats only, a gross necropsy of heart, lungs, and pulmonary vessels was performed immediately after municipal euthanasia. Plasma from each cat was tested for anti–D. immitis antibodies and D. immitis antigens using in-house antibody and antigen tests. In the 1991–1992 study, 21 of 242 dogs (8.7%) were positive for D. immitis. The prevalence of heartworm in dogs increased to 12.7% (47 of 369 dogs) in 1999–2000. Another species of filarial worm, Dipetalonema reconditum, also was observed in blood samples from dogs (18 of 242 dogs [7.44%] and 28 of 369 dogs [7.6%] in 1991–1992 and 1999–2000, respectively). The prevalence of the nonpathogenic D. reconditum was not significantly different from that of D. immitis, emphasizing the importance of correct diagnosis of circulating microfilaria. Modified Knotts' and gross necropsy of cats revealed no heartworms, but 5 of 71 (7%) plasma samples were positive for heartworm antibodies.