Mosquito Bednets and Spray Fallacies

    The first significant contradiction to the idea that once infection of humans has begun the only remedy or protection for the public is to utilize insecticidal spray is the idea that spray alone can solve the problem; that there are no alternatives. The simple truth is that for some time now research sponsored by the World Health Organization (WHO) in a number of different areas has come to the conclusion that the only really effective management and prevention of transmission of mosquito-borne disease is to utilize mosquito bed nets. In contrast, the domiciliar application of DDT, which has been promoted by the WHO for years, proves entirely ineffective in many areas due to resistance in the vectors.

    A publication by one such research group in Colombia (Rojas, 2001) provides a detailed review of the measures that are effective. The principal core of effective measures does not involve any direct activities against the mosquito populations. Instead it focuses on public health education, community development and availability of primary health care. The goal of these measures is to produce a long-term adjustment in cultural practices around water management, health-care seeking behavior and the utilization of mosquito bed nets. The bed net component alone has been demonstrated to be markedly more effective than insecticidal management of the vector populations.

    The second fallacy of the claim about spray being the only possible measure has to do with the natural dynamics of the transmission of WNv. The best ecological modeling of WNv (Bowman, 2005 and Wonham, 2005) and related flavivirus transmission (Newton, 1992) comes to a completely different conclusion about the idea of any reduction of the infected vector population producing a complementary reduction in transmission to people. The simplified statement of it is that anything less than complete elimination of the infected vector population may only end up delaying the peak of the epizootic in the birds; hence protracting the period of potential human exposure instead of minimizing it. An additional conclusion from the mathematical models, equally important, is that the only effective measures at providing the kind of reductions in the vector populations that would be needed to extinct the virus locally have to be applied against the early season larval populations, and not the late season adult populations of the vectors.  So, the clear scientific message about control measures is that larvaciding early in the season is effective, whereas adulticiding is not effective at any time, particularly when vector control districts tend to do it.

    Instead of a good review of the science in advance of aerial spray application, we have been subjected to a poorly designed experiment without any good scientific sampling to review the results. The whole policy is based on axiomatic claims such as the insistence that spray is the only protective measure, or that the spray is even effective at all.