title: Ivermectin acts as a posteclosion nymphicide by reducing blood feeding of human head lice (Anoplura: Pediculidae) that hatched from treated eggs.
abstract: The 0.5% ivermectin topical cream formulation was not directly ovicidal to treated eggs of head lice, as hatchability was not decreased. Nevertheless, the percent of hatched lice from treated eggs that took a blood meal significantly decreased (80-95%) compared with lice that hatched from untreated eggs and all treated lice died within 48 h of hatching, including those that fed. Dilutions of ivermectin formulation of 0.15 and 0.2 microg/ml, which were topically applied to 0-8 d old eggs, were not lethal to lice at 24 h posteclosion. However, 9 and 16% less lice fed when hatched from these treated eggs, respectively. Total [3H] inulin ingested by untreated first instars significantly increased over a 48 h feeding interval but was significantly less in instars that hatched from eggs receiving the 0.15 (36% less) and 0.2 (55% less) microg/ml ivermectin treatments compared with placebo. The reduced feeding that occurred after the 0.15 and 0.2 microg/ml ivermectin treatments occurred in the absence of mortality and suggests a unique mode of action of ivermectin on feeding that is separate from the mode of action of ivermectin leading to mortality. Failure of hatched instars to take a blood meal after egg treatments with formulated ivermectin is likely responsible for its action as a posteclosion nymphicide.
authors.affiliation: Department of Veterinary and Animal Science, Morrill 1, N311B, 639 N. Pleasant Street, University of Massachusetts, Amherst, MA 01003, USA.
authors.forename: Joseph P
authors.initials: JP
authors.lastname: Strycharz
authors.forename: Noah M
authors.initials: NM
authors.lastname: Berge
authors.forename: Anna-Maria
authors.initials: AM
authors.lastname: Alves
authors.forename: J Marshall
authors.initials: JM
authors.lastname: Clark
mesh_terms: D000818:Animals; D018118:Chloride Channels; D005247:Feeding Behavior / Q000187:drug effects*; D006801:Humans; D007306:Insecticides / Q000633:toxicity*; D007559:Ivermectin / Q000633:toxicity*; D009758:Nymph / Q000187:drug effects; D010063:Ovum / Q000187:drug effects*; D010374:Pediculus / Q000187:drug effects*
chemical_list: D018118:Chloride Channels; D007306:Insecticides; C109777:glutamate-gated chloride channels; D007559:Ivermectin