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.