Spatial and Temporal Variation in the Seroprevalence of Canine Heartworm Antigen in the Island Fox

Abstract

Island foxes (Urocyon littoralis) are endemic to six of the eight California Channel Islands (USA). The island fox is classified as a threatened species by the State of California, and recently three of the six subspecies have experienced abrupt population declines. As part of a continuing effort to determine the cause of the declines, we tested island fox serum samples collected in 1988 (n ϭ 176) and 1997-98 (n ϭ 156) over the entire geographic range of the species for seroprevalence of canine heartworm (Dirofilaria immitis) antigen. Using a commercially available enzyme-linked immunosorbent assay (PetChek , Idexx Laboratories, Westbrook, Maine, USA) we detected heartworm antigen in four of the six populations of island foxes. On San Miguel and Santa Rosa Islands, seroprevalence in adult foxes was Ͼ85% (n ϭ 62) in 1988 and increased to 100% (n ϭ 24) in 1997-98. On Santa Cruz Island, seroprevalence in adult foxes decreased from 83% (n ϭ 30) to 58% (n ϭ 26), whereas on San Nicolas Island, seroprevalence increased from 25% (n ϭ 32) to 77% (n ϭ 30) during the same period. All of the pups assayed (n ϭ 33) were seronegative. The seroprevalences of heartworm reported herein for the four populations of island foxes are the highest yet reported for a fox species. However, additional demographic data reported elsewhere suggests that heartworm has not been a major factor in the recent declines of island fox populations.

Golden eagles, feral pigs, and insular carnivores: How exotic species turn native predators into prey

“…Disease was initially suspected as a contributing agent, but the distribution of micro-and macroparasites was incongruent with fox demographic patterns, suggesting that disease played no role (15,30,32). Further, a generalist pathogen like rabies or distemper, the most common causes of disease-driven declines in carnivores (33), is unlikely to be responsible for the decline in foxes because a decline in the population size of skunks would be expected as well.…”

Canine heartworm (Dirofilaria immitis) in Fresno and Madera Counties, California: Prevalence differences between foothill and valley habitats

“…In parts of northern California, heartworm prevalence in coyotes was shown to be as high as 57% (Sacks and CaswellChen, 2003), and on four of the California Channel Islands, prevalence of heatworm antigen in island foxes varied between 25% and 100%, with a notable increase in prevalence between 1988 and 1998. In the latter case, necropsies failed to find any adult heartworms in the island foxes, possibly indicating false positive serology (Roemer et al, 2000;Coonan et al, 2005). Coyotes and foxes may be assumed to spend all of their time outdoors, not be prophylactically treated, and to not be receiving veterinary care.…”

Prevalence of Dirofilaria immitis Infection in Living Raccoon Dogs Assessed by Hematological Examination

“…Second, a postmortem examination may have had higher sensitivity than hematological examination for young raccoon dogs because postmortem examination can detect immature worms. On the other hand, earlier reports described that the antigen-based methods had greater sensitivity than earlier studies of heartworm prevalence in canids that could identify adult worms and microfilariae in tissues and blood [11,12]. This criterion may be fulfilled in the high-age population, e.g., in domestic dogs.…”

“…Several wild animals are known to be infected with this parasite, including wolves (Canis lupus) [14], free-ranging coyotes (Canis latrans) [4], island foxes (Urocyon littoralis) [11], harbor seal (Phoca vitulina) [3], and black-footed ferrets (Mustela nigripes) [17]. D. immitis has also been detected in other non-carnivore species: free-ranging armadillos (Dasypodidae) [1], pale-headed saki monkeys (Pithecia pithecia) [2], and horse [15].…”