title: Infection with Colorado tick fever virus among humans and ticks in a national park and forest, Wyoming, 2010.
abstract: BACKGROUND
  Colorado tick fever (CTF) is an underreported tick-borne viral disease occurring in the western United States. CTF illness includes fever, headache, and severe myalgia lasting for weeks. Wyoming has one of the highest CTF incidence rates with approximately 30% of infected persons reporting tick exposure in a Wyoming National Park or Forest before symptom onset. We assessed CTF virus infections among humans and Dermacentor andersoni ticks in Grand Teton National Park (GRTE) and Bridger-Teton National Forest (BTNF).
  
  
  METHODS
  In June of 2010, 526 eligible employees were approached to participate in a baseline and 3-month follow-up serosurvey and risk behavior survey. Seropositivity was defined as antibody titers against CTF virus ≥10, as measured by the plaque reduction neutralization test. Ticks were collected at 27 sites within GRTE/BTNF and tested by RT-PCR for the CTF virus.
  
  
  RESULTS
  A total of 126 (24%) employees participated in the baseline and follow-up study visits. Three (2%) employees were seropositive for CTF virus infection at baseline. During the study, 47 (37%) participants found unattached ticks on themselves, and 12 (10%) found attached ticks; however, no participants seroconverted against CTF virus. Walking through sagebrush (p=0.04) and spending time at ≥7000 feet elevation (p<0.01) were significantly associated with tick exposure. Ninety-nine percent (174/176) of ticks were D. andersoni, and all were found at ≥7000 feet elevation in sagebrush areas; 37 (21%) ticks tested positive for CTF virus and were found at 10 (38%) of 26 sites sampled.
  
  
  CONCLUSIONS
  Although no GRTE or BTNF employees were infected with CTF virus during the study period, high rates of infected ticks were identified in areas with sagebrush at ≥7000 feet. CTF education and personal protection measures against tick exposure should be targeted to visitors and employees traveling to the high-risk environs identified in this study.
authors.affiliation: 1 Epidemic Intelligence Service, Centers for Disease Control and Prevention , Atlanta, Georgia .
authors.forename: Aimee L
authors.initials: AL
authors.lastname: Geissler
authors.forename: Emily
authors.initials: E
authors.lastname: Thorp
authors.forename: Clayton
authors.initials: C
authors.lastname: Van Houten
authors.forename: Robert S
authors.initials: RS
authors.lastname: Lanciotti
authors.forename: Nicolas
authors.initials: N
authors.lastname: Panella
authors.forename: Betsy L
authors.initials: BL
authors.lastname: Cadwell
authors.forename: Tracy
authors.initials: T
authors.lastname: Murphy
authors.forename: J Erin
authors.initials: JE
authors.lastname: Staples
mesh_terms: D000328:Adult; D000368:Aged; D000818:Animals; D000914:Antibodies, Viral / Q000097:blood*; D003121:Colorado Tick Fever / Q000453:epidemiology* / Q000821:virology; D003122:Colorado tick fever virus / Q000276:immunology* / Q000302:isolation & purification; D003870:Dermacentor / Q000821:virology*; D005260:Female; D005500:Follow-Up Studies; D065928:Forests; D006801:Humans; D008297:Male; D008875:Middle Aged; D014959:Wyoming / Q000453:epidemiology; D055815:Young Adult
chemical_list: D000914:Antibodies, Viral
keywords: Colorado tick fever; Dermacentor andersoni; Wyoming