Filariasis in Coyotes from Kansas and Colorado

Abstract

Prevalence of Dirofilaria immitis in a sample of 133 coyotes (Canis latrans) from Kansas and Colorado was determined during winter, 1972. Adult heartworms were found in 11 of 133 coyotes examined (8%). Among coyotes from northeastern Kansas, 9 of 111 (8% ) were infected with D. immitis. Neither of 2 coyotes from central Kansas was infected, but 2 of 20 eastern Colorado coyotes (10%) were infected with D. immitis. The highest percentage (30%) of D. immitis infection occurred among coyotes aged 5 to 6 years, although 3 yearling coyotes were infected. Single sex infections with D. immitis occurred in 5 of 11 coyotes, and maximum worm burden was 12. Based on local bounty records for 1949 to 1969, the average estimated number of adult coyotes in 450 sq. miles of Leavenworth County, Kansas, was 250 or 1 adult coyote for each 1.8 sq. mile. In any year approximately 20 adult coyotes in the county would contain 1 or more adult D. immitis; however, only 10 of these 20 coyotes would contain both sexes of D. immitis and would be capable of producing microfilariae. In Leavenworth County coyotes infected with D. immitis were estimated to comprise less than 1% of infected canine hosts. Although the canine heartworm, Dirofilaria immitis (Leidy), is most often reported in domestic dogs, it has also been found in domestic cats (Bernard, 1970) and wild canines. Faust et al. (1941) reported the occurrence of D. immitis in the wolf (Canis floridanus) in Louisiana, and Erickson (1944) reported it in a red fox (Vulpes fulva) from New York. Gier and Ameel (1957) found heartworms in 10 coyotes (Canis latrans) from Kansas. Unfortunately most published reports of D. immitis in wild mammals only represent the occurrence of an isolated infection (Hirth and Nielsen, 1966), and surveys for heartworms in wild mammals have been infrequent. Few published surveys of wild mammal parasites have included an estimate of the mammal population size as did Gier (1957), and wild mammal surveys have not often been carried out in an area from which comparative data on the prevalence of D. immitis in domestic dogs has also been available (Schlotthauer, 1964; Schlotthauer and Griffiths, 1964). A number of authors have concluded that wild mammal populations are not significant as reservoirs of D. immitis infection (Schlotthauer, 1964; Otto, 1969). This conclusion seems to be based on the absence of any reported high rate of D. immitis infection among wild mammals surveyed. Because published Received for publication 19 August 1974. * Present address: Department of Zoology, University of Michigan, Ann Arbor, Michigan 48104. surveys of heartworm in wild mammals are so scarce, however, this conclusion should be supported with additional data. The availability of coyote carcasses in northeastern Kansas permitted study of the occurrence of D. immitis in 133 coyotes (Canis latrans) necropsied during winter 1972. Comparable data on the prevalence of heartworm in domestic dogs from northeastern Kansas have been reported previously (Graham, 1974). MATERIALS AND METHODS Coyote carcasses were obtained for examination from a fur buyer in northeastern Kansas through whose cooperation coyotes were sorted according to area of origin when purchased from hunters. Of the 133 coyotes examined the majority (111) came from 4 counties in northeastern Kansas: Leavenworth, Jefferson, Douglas, and Atchison. Two coyotes came from Saline County in central Kansas. Although the counties of origin could not be determined, the remaining 20 coyotes came from eastern Colorado. Coyote sex was recorded, and age was determined according to dental wear pattern (Gier, 1957). The right auricle and ventricle and their associated blood vessels were examined for adult heartworms, but the lungs were not examined separately. Some heartworms might have undergone postmortem migration into the lungs and been overlooked, and very small heartworms might have been missed in the large masses of frozen blood frequently found in the hearts. The prevalence of D. immitis in coyotes could therefore be somewhat higher than indicated by the examinations. When an animal was found infected with D. immitis, the heart and filarial worms were removed and pre-