Sunday, August 19, 2007


Ever the creative purveyor of misinformation, Tim Lambert proclaims: "Study finds that DDT not the most effective for IRS". The study Lambert refers to, but does not link to, did not aim to identify the most effective insecticide for indoor residual spraying -- only three chemicals were tested -- but rather looked at the relative importance of toxicity, repellency and irritancy as factors to consider when deciding which chemical to use for IRS. The study's authors concluding:
Based on the combination of laboratory and confirmatory field data, we propose a new paradigm for classifying chemicals used for vector control according to how the chemicals actually function to prevent disease transmission inside houses. The new classification scheme will characterize chemicals on the basis of spatial repellent, contact irritant and toxic actions.
So Lambert's readers have been misled without even reading the contents of his post, which is, of course, also misleading. Amongst which:
The experience in Sri Lanka where DDT resistance led to a malaria epidemic despite DDT spraying also points to the wisdom of switching.
Sri Lanka's malaria resurgence cannot be blamed solely on DDT resistance: it was a complex situation characterized by bureaucratic ineptitude and the misuse of DDT:
The reasons for the upsurge were many. It was certainly facilitated by the backlog of slides accumulated in the laboratories and the comparatively low numbers of blood smears taken by health institutions that permitted a gradual build up of undetected, untreated cases. Intradomiciliary residual spraying with DDT had been withdrawn in the early 1960s because of the low number of cases (in accordance with the criteria for passing from attack to consolidation). After the resurgence was recognized, administrative and financial difficulties prevented the purchase of insecticides of which there was no residual stock, and the employment of temporary squads for spraying them when insecticides were donated. In 1968, the programme reverted from consolidation to attack phase, but by that time malaria had already taken root again in all previously endemic areas. DDT residual spraying was again applied on a total coverage basis, accompanied in some areas by mass radical treatment. These measures met with limited success, but the malaria situation deteriorated once more between 1972 and 1975. Apart from operational and administrative shortcomings, the main reason for this second increase was the development of vector resistance to DDT, to such an extent that it was necessary to change to the more expensive malathion in 1977.
Lambert is not to be trusted, ever.

Update: Malaria expert Donald Roberts on the efficacy of DDT:
Research that I and my colleagues recently conducted shows that DDT is the most effective pesticide for spraying on walls, because it can keep mosquitoes from even entering the room.
So, who to believe, a malaria expert or a computer teacher?


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