title: Seasonal activity patterns of the western black-legged tick, Ixodes pacificus, in relation to onset of human Lyme disease in northwestern California.
abstract: Seasonal activity patterns of questing western black-legged ticks, Ixodes pacificus were investigated in northwestern California. Adult I. pacificus became active in the fall (late October/early November) and their appearance was associated with the first rain of the season. Following a peak in January, the abundance of adult ticks declined such that they were rare or absent by June/July. The nymphal tick activity season occurred from January through October, and larval activity occurred from April to June, but sometimes extended into October. Thus, potentially infectious ticks (nymphs and adults) present a year-round risk of Lyme disease transmission in northwestern California. The seasonality of Lyme disease cases in humans, based on the onset of erythema migrans, mirrored tick activity patterns and was year-round in cases infected in California. Peak incidence in humans occurs from May through July, and indicates that most disease transmission is from nymphal ticks. This study demonstrates that tick activity patterns are more extended than previously recognized in northwestern California.
authors.affiliation: Vector-borne Disease Section, California Department of Public Health, United States. Electronic address: dansalkeld@gmail.com.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Salkeld
authors.affiliation: Vector-borne Disease Section, California Department of Public Health, United States.
authors.forename: Martin B
authors.initials: MB
authors.lastname: Castro
authors.affiliation: Vector-borne Disease Section, California Department of Public Health, United States.
authors.forename: Denise
authors.initials: D
authors.lastname: Bonilla
authors.affiliation: Vector-borne Disease Section, California Department of Public Health, United States.
authors.forename: Anne
authors.initials: A
authors.lastname: Kjemtrup
authors.affiliation: Vector-borne Disease Section, California Department of Public Health, United States.
authors.forename: Vicki L
authors.initials: VL
authors.lastname: Kramer
authors.affiliation: Department of Environmental Science, Policy and Management, University of California, Berkeley, United States.
authors.forename: Robert S
authors.initials: RS
authors.lastname: Lane
authors.affiliation: Vector-borne Disease Section, California Department of Public Health, United States.
authors.forename: Kerry A
authors.initials: KA
authors.lastname: Padgett
mesh_terms: D000818:Animals; D001096:Arachnid Vectors / Q000382:microbiology*; D025065:Borrelia burgdorferi / Q000502:physiology*; D002140:California / Q000453:epidemiology; D005260:Female; D005929:Glossitis, Benign Migratory / Q000453:epidemiology*; D006801:Humans; D018884:Ixodes / Q000382:microbiology*; D007814:Larva; D008193:Lyme Disease / Q000453:epidemiology*; D009758:Nymph; D012621:Seasons
keywords: Borrelia burgdorferi; Ixodes pacificus; Phenology; Seasonality; Western black-legged tick