Contributions to the ecology of Colorado tick fever virus.

Abstract

Studies were conducted in 3 different habitats in Mill Canyon, Ravalli County, in southwestern Montana on certain biological phenomena that affect the dispersal and maintenance of Colorado tick fever in its natural biocenose. During the study 399 small mammals were captured, in descending order of frequency: Peromyscus maniculatus, Citellus lateralis, Neotoma cinerea, Eutamias amoenus, Clethrionomys gapperi, Microtus longicaudus and Glaucomys sabrinus. Capture-recapture data did not prove amenable to statistical treatment, so comparisons of population levels were made by animals caught per-trap-night. Of the rodents collected, P. maniculatus proved most amenable to manipulation, and populations of this species were stable and uniformly distributed throughout the study area. Adult D. andersoni occurred primarily in alpine meadows; larvae mainly in rock ledges in the same area; nymphs for the most part did not respond to the CO2 technique. Adults and nymphs were active during May to July, while larvae were collected July and August. Infestation of rodents ranged from 16% in C. gapperi to 100% in C. lateralis. C. lateralis and N. cinerea were most often infested: average 7–12 ticks per capture. Ixodes ochotonae was also recorded in the study area. Virus was isolated 32 times from pools of D. andersoni nymphs and larvae off rodents but never from wild-caught unfed larvae. Positive pools ranged from 15% in 1964 to 35% in 1966. The greatest number of positive pools (20–53%) was taken from C. lateralis and N. cinerea. In 1964, 11 of 315 P. maniculatus blood samples, 3.5%, were positive for CTF virus; in 1966, 4 of 68 rodent blood samples, 5.9%, were positive. These latter isolations consisted of 2 samples from P. maniculatus and 2 from C. lateralis. The significance of the data gained in this study in the maintenance of CTF virus within the biocenose is discussed.