Some good points, Mark, about ways of knowing things, and ways of
bringing about desirable (or desired, not the same thing) changes.
DDT is toxic, period, that's how it works. It is an effective
insecticide. A very low dose sprayed on interior walls of houses in
malarial areas, because the vector mosquitos rest on the walls during
the day, reduces the vector population directly at the location where
parasite transmission occurs -- the home. The pesticide industry has
promoted this treatment extensively, as has WHO.
Now, it is also known that the vectors, just like other insects, evolve
resistance, specifically because of this effective treatment protocol,
with its low dose rate and the partitioned environment with untreated
refuges. So, in places where DDT has been used (and it continues to be
used) for the longest periods of time, it is least effective.
The pesticide industry does not produce bed nets, which are equally
effective, less expensive, and the vectors develop no resistance. So,
the pesticide industry does not promote them, and WHO doesn't advocate
them consistently, though it does at times and in places.
No good data exist that explain why malaria has become a non-problem in
the U.S., but it is not because we spray our homes with DDT. We
don't. But malaria was endemic (I use the term here in its clinical
application) to much of the U.S. in the 19th and early 20th centuries.
It disappeared in the early 20th century, prior to the advent of DDT,
and has not returned. If we could determine why, rather than
speculating about why, we would have something extremely valuable to
offer to places where malaria, still the most deadly and economically
costly disease known, still occurs.
DDT was banned because of data showing its long persistence and harm.
Further data now show it has substantial effects on vertebrate animals
that were supposedly unaffected, including its metabolites acting as
As you observed, Mark, things are not so simple as they seem.
David L. McNeely, Ph.D., Professor of Biology
Langston University; P.O. Box 1500
Langston, OK 73050; email: dlmcneely at lunet.edu
telephone: (405) 466-6025; fax: 405) 466-3307
home page http://www.lunet.edu/mcneely/index.htm
"Where are we going?" "I don't know, are we there yet?"
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