Pyrethroids
are one of the most commonly used classes of insecticides,
and their acid and alcohol components are esterase degradation products,
usually considered to be biologically inactive. In this study, it
was found that several pyrethroid acids had a spatial repellent activity
that was greater than DEET, often more active than the parent pyrethroids,
and showed little cross resistance in a pyrethroid-resistant Puerto
Rico strain of Aedes aegypti mosquitoes. Further
investigation revealed that the acids can synergize not only contact
repellent standards but also other pyrethroid components as well as
the parent pyrethroids themselves. Synergism by the pyrethroid acids
is expressed as both increased spatial repellency and vapor toxicity
as well as human bite protection. Electrophysiological studies confirmed
that pyrethroid acids (100 μM) had no effect on neuronal discharge
in larval Drosophila melanogaster CNS and were detected
by electroantennography, and there was little resistance to olfactory
sensing of these acids in antennae from Puerto Rico strain mosquitoes
carrying kdr mutations. Thus, the data suggest that the pyrethroid
acids have a different mode of action than the parent pyrethroids,
unrelated to the voltage-sensitive sodium channel. The results highlight
the potential of pyrethroid acids to be useful in future repellent
formulations.
Military forces and the recreational industry rely on the repellent properties of permethrin-treated fabrics and N,N-diethyl-meta-toluamide (deet)–based lotions to provide protection from disease vectors and hematophagous organisms. Concerns regarding efficacy have been raised as pyrethroid resistance becomes more common and recent publications present contradictory conclusions. In this preliminary study, consenting volunteers were exposed to pyrethroid-susceptible and pyrethroid-resistant Aedes aegypti strains while wearing sleeves of untreated or permethrin-treated army uniform fabric as well as with untreated or deet-treated exposed forearms. Deet was nearly 100% effective against both susceptible and resistant strains. However, permethrin treatment provided no significant protection against the resistant Puerto Rico strain relative to untreated control sleeves. These results confirm that pyrethroid-resistant vectors can negate the efficacy of permethrin-treated uniforms. Additional testing with resistant field strains is needed to better understand the risk to service members.
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