Tick infestations of the eastern cottontail rabbit (Sylvilagus floridanus) and small rodentia in northwest Alabama and implications for disease transmission.

Abstract

Studies were conducted over a four-county area of northwest Alabama to determine the association of eastern cottontail rabbits with Dermacentor variabilis, the eastern United States vector of Rocky Mountain spotted fever. A secondary objective was to compare infestations of this tick on rabbits with infestations on commonly encountered rodent species as a means of determining the relative importance of each in the disease transmission cycle. These epidemiologic surveys were conducted in response to reported fatal cases of Rocky Mountain Spotted Fever in two counties of the study area. From 202 eastern cottontail rabbits, 3,956 ticks were collected. Of this total, 79.87% were Haemphysalis leporispalustris, 9.15% Amblyomma americanum, 8.22% Ixodes dentatus, and 2.76% D. variabilis. Only immature stages of D. variabilis were collected from cottontail rabbits. Ticks were collected on rabbits in all months except November, and only one specimen was taken in January. Based on the average number of ticks per host collected in each month, April was the peak month for D. variabilis and I. dentatus. High values for H. leporispalustris also occurred at this time, but even higher values occurred in October and December. The heaviest infestation of A. americanum occurred during the month ofAugust and coincides with the activity period for the larvae of this species. Two hundred sixty-nine of the smaller Rodentia, comprising 13 species, yielded 264 ticks, all D. variabilis, and all but two were immature stages. Five rodent species, Microtus ochragaster Orozomys palustris, Peromyscus gossypinus, Peromyscus leucopus, and Sigmodon hispidus accounted for 95.83% of the ticks collected, and appeared to be preferred hosts for D. variabilis; all five had higher infestation levels per host than did the eastern cottontail rabbit. Data on host relationships in association with seasonal activity are presented.