Differential permethrin susceptibility of head lice sampled in the United States and Borneo.
BACKGROUND
Pediculiasis is treated aggressively in the United States, mainly with permethrin- and pyrethrin-containing pediculicides. Increasingly frequent anecdotal reports of treatment failure suggest the emergence of insecticidal resistance by these lice.


OBJECTIVE
To confirm or refute the susceptibility of head lice sampled in the United States to permethrin.


METHODS
Survey. Head lice were removed from children residing where pediculicides are readily available and where such products are essentially unknown. Their survival was compared following exposure to residues of graded doses of permethrin in an in vitro bioassay.


METHODS
School children from Massachusetts, Idaho, and Sabah (Malaysian Borneo).


METHODS
In the United States, 75 children aged 5 to 8 years. In Sabah, 59 boys aged 6 to 13 years. Virtually all sampled US children had previously been treated with pediculicides containing pyrethrins or permethrin; none of the Sabahan children were so exposed.


METHODS
Survival of head lice exposed to permethrin.


RESULTS
Permethrin did not affect head lice sampled from chronically infested US children who had previously been treated for pediculiasis. The slope of the dose-response regression line for these lice did not differ significantly from zero (P = .66). This pediculicide immobilized lice sampled in Sabah. Mortality correlated closely with permethrin concentration (P = .008).


CONCLUSIONS
Head lice in the United States are less susceptible to permethrin than are those in Sabah. The pyrethroid susceptibility of the general population of head lice in the United States, however, remains poorly defined. Accordingly, these relatively safe over-the-counter preparations may remain the pediculicides of choice for newly recognized louse infestations.
Pollack
R J
RJ
Harvard School of Public Health, Boston, Mass. 02115, USA. rpollack@hsph.harvard.edu
Kiszewski
A
A
Armstrong
P
P
Hahn
C
C
Wolfe
N
N
Rahman
H A
HA
Laserson
K
K
Telford
S R
SR
Spielman
A
A
D000293:Adolescent; D000818:Animals; D001893:Borneo; D002648:Child; D004305:Dose-Response Relationship, Drug; D006801:Humans; D007061:Idaho; D007305:Insecticide Resistance; D007306:Insecticides / Q000494:pharmacology* / Q000627:therapeutic use; D010373:Lice Infestations / Q000188:drug therapy*; D016014:Linear Models; D008297:Male; D008404:Massachusetts; D010374:Pediculus / Q000187:drug effects*; D026023:Permethrin; D011722:Pyrethrins / Q000494:pharmacology* / Q000627:therapeutic use; D012536:Scalp Dermatoses / Q000188:drug therapy*
D007306:Insecticides; D011722:Pyrethrins; D026023:Permethrin