Entomological evaluation of community-wide use of lambdacyhalothrin-impregnated bed nets against malaria in a border area of north-west Thailand.

This paper reports 2 studies. (i) After a year of baseline data collection, lambdacyhalothrin-treated bed nets were introduced into 3 of 5 villages in north-west Thailand, the remaining 2 being treated with placebo. Human bait collections were carried out in each village on 2 nights per month, for 8 months of each year, and the biting densities were compared between the first year and the second year. The treated bed nets did not have any significant impact on the density or parous rates of Anopheles sawadwongporni and A. maculatus s.s. populations. The results for A. dirus s.l. were not conclusive because of the low number caught. Significant reductions in biting and parous rates of A. minimus species A were observed in only one of the 3 treated villages, and there was no overall difference between treated and control groups. However, the trial suffered from the washing of nets by villagers and the low rate of reimpregnation. (ii) A short-term study involved 4 villages in a cross-over design, and lasted 48 d. For the first 24 d, residents of 2 villages were given new treated nets while the other 2 villages retained their own untreated nets. For the second 24 d, this situation was reversed. Daily light-trapping revealed no significant difference in the indoor densities or parous rates of A. minimus species A between the periods with treated or untreated nets.(ABSTRACT TRUNCATED AT 250 WORDS)