Relationship between Skin-Sensitizing Antibody Production in the Snowshoe Hare, Lepus americanus, and Infestations by the Rabbit Tick, Haemaphysalis leporispalustris (Acari: Ixodidae)

Abstract

commonly occurs in Southeastern Louisiana horses and ponies, and that the prevalence rates are higher when adults rather than circulating microfilariae are considered. Circulating microfilaria levels are generally low and do not show a periodicity. The prevalence of adults in ponies is considerably higher than previous reports of a 7% prevalence in Kentucky Thoroughbreds (Lyons et al., 1983, American Journal of Veterinary Research 44: 839-844) or a 19% prevalence rate in horses and mules in Panama (Foster, 1936, Journal of Parasitology 22:479-510). There is an apparent difference in the prevalence of circulating microfilariae between adult ponies and horses examined. However, the 2 pony herds sampled for microfilariae were located within city limits where an active mosquito control program exists. This potential reduction in vectors could be responsible for the low prevalence of infection in these ponies. The percentage of microfilaria positive horses and the number of circulating microfilariae decreased with an increase in the animal age. Weinmann et al. (1973, Journal of Wildlife Diseases 9: 213-220) observed a similar trend in Setaria yehi infected black-tailed mule deer in Northern California. Our observations suggest that either an age resistance or acquired immunity against microfilariae develops in the horse. The data recovered from foals and yearlings suggest a natural prepatent period of 8 to 12 mo in animals naturally infected on pastures in this region.