Posted by Vector and Vector-borne Disease Committee
August 2, 2022
Kerry A. Padgett,1 Anne Kjemtrup,1 Mark Novak,1 Jason O. Velez,2 and Nicholas Panella2
1Vector-Borne Disease Section, California Department of Public Health, Sacramento, California, USA.
2Division of Vector-Borne Diseases, Centers for Disease Control and Prevention, Fort Collins, Colorado, USA.
Vector-Borne and Zoonotic Diseases. 2022. DOI: 10.1089/vbz.2022.0018
Abstract [condensed]. In the past few decades, reported human cases of Colorado tick fever in the western United States have decreased dramatically. … This study conducted surveillance for Colorado tick fever virus (CTFV) in Dermacentor ticks in recreational sites in Colorado, Wyoming, and California to determine whether the virus is still present. Adult Rocky Mountain wood ticks (Dermacentor andersoni), Pacific Coast ticks (Dermacentor occidentalis), and winter ticks (Dermacentor albipictus) were tested by PCR and a subset of PCR-positive D. andersoni ticks (n = 7) were cultured in Vero cells. CTFV-positive Rocky Mountain wood ticks were found in all states: Colorado (58% prevalence), Wyoming (21%), and California (4%). Although no winter ticks tested positive, Pacific Coast ticks tested positive in one county (Siskiyou County, 15% prevalence) and were positive only in a location that also maintained Rocky Mountain wood ticks and golden mantled ground squirrels, a known CTFV host. In summary, although the number of human CTFV cases has declined dramatically, this decrease in reported disease does not appear to be due to the disappearance or even the decline in prevalence of this virus in ticks in historically endemic regions of the country.
Note: This and related recent studies continue to emphasize the public health importance of multiple tick species. Although the incidence of human infection has remained low and restricted geographically in California, landscape and climate change have been shown to enhance transmission.