title: Expansion of the Knockdown Resistance Frequency Map for Human Head Lice (Phthiraptera: Pediculidae) in the United States Using Quantitative Sequencing.
abstract: Pediculosis is a prevalent parasitic infestation of humans, which is increasing due, in part, to the selection of lice resistant to either the pyrethrins or pyrethroid insecticides by the knockdown resistance (kdr) mechanism. To determine the extent and magnitude of the kdr-type mutations responsible for this resistance, lice were collected from 138 collection sites in 48 U.S. states from 22 July 2013 to 11 May 2015 and analyzed by quantitative sequencing. Previously published data were used for comparisons of the changes in the frequency of the kdr-type mutations over time. Mean percent resistance allele frequency (mean % RAF) values across the three mutation loci were determined from each collection site. The overall mean % RAF (±SD) for all analyzed lice was 98.3 ± 10%. 132/138 sites (95.6%) had a mean % RAF of 100%, five sites (3.7%) had intermediate values, and only a single site had no mutations (0.0%). Forty-two states (88%) had a mean % RAF of 100%. The frequencies of kdr-type mutations did not differ regardless of the human population size that the lice were collected from, indicating a uniformly high level of resistant alleles. The loss of efficacy of the Nix formulation (Prestige Brand, Tarrytown, NY) from 1998 to 2013 was correlated to the increase in kdr-type mutations. These data provide a plausible reason for the decrease in the effectiveness of permethrin in the Nix formulation, which is the parallel increase of kdr-type mutations in lice over time.
authors.affiliation: Molecular and Cellular Biology Program, University of Massachusetts, Amherst, MA 01003 (kgellatl729@gmail.com).|Current address: Department of Molecular Pharmacology, University of Massachusetts Medical School, Worchester, MA.
authors.forename: Kyle J
authors.initials: KJ
authors.lastname: Gellatly
authors.affiliation: Department of Veterinary and Animal Sciences, University of Massachusetts, Amherst, MA 01003 (skrim@umass.edu; jclark@vasci.umass.edu).
authors.forename: Sarah
authors.initials: S
authors.lastname: Krim
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Massachusetts, Amherst, MA 01003 (danpalenchar@gmail.com).|Current address: Nutrition Science Initiative (NuSI), San Diego, CA.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Palenchar
authors.affiliation: The Shepherd Institute for Lice Solutions, West Palm Beach, FL 33407 (katie@licesolutions.org).
authors.forename: Katie
authors.initials: K
authors.lastname: Shepherd
authors.affiliation: Department of Biological Sciences and Environmental Sciences Program, Southern Illinois University, Edwardsville, IL 62026 (kyoon@siue.edu).
authors.forename: Kyong Sup
authors.initials: KS
authors.lastname: Yoon
authors.affiliation: Department of Microbiology, University of Massachusetts, Amherst, MA 01003 (christopher.rhodes710@gmail.com).|Current address: Department of Veterinary and Animal Sciences, University of Massachusetts, Amherst, MA.
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Rhodes
authors.affiliation: Department of Agricultural Biotechnology, Seoul National University, Seoul, 151-921, South Korea (shlee22@snu.ac.kr).
authors.forename: Si Hyeock
authors.initials: SH
authors.lastname: Lee
authors.affiliation: Department of Veterinary and Animal Sciences, University of Massachusetts, Amherst, MA 01003 (skrim@umass.edu; jclark@vasci.umass.edu), jclark@vasci.umass.edu.
authors.forename: J
authors.initials: J
authors.lastname: Marshall Clark
mesh_terms: D000483:Alleles; D000818:Animals; D006801:Humans; D007305:Insecticide Resistance; D007306:Insecticides / Q000494:pharmacology*; D010373:Lice Infestations / Q000469:parasitology*; D009154:Mutation; D010374:Pediculus / Q000187:drug effects* / Q000235:genetics*; D011722:Pyrethrins / Q000494:pharmacology; D014481:United States
chemical_list: D007306:Insecticides; D011722:Pyrethrins
keywords: Pediculus humanus capitis; human head louse; knockdown resistance frequency; quantitative sequencing