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Bryan's Blog 2005/03/16
DDT and Malaria
I started my series of responses to State of Fear (SOF) thinking that I was going to be commenting on climate change issues alone. However, Crichton goes off on a lot of tangents, and I now understand why, having understood that State Of Fear is essentially a novel written around a speech where he makes a fairly strong pitch that environmentalism is a new religion. Much of what he says is very fair, not least:
Because in the end, science offers us the only way out of politics. And if we allow science to become politicized, then we are lost.
but then he proceeds to write a book which is undisguised "lobbying" in the worst political sense ... a book which finishes with what I hope is a tongue in cheek claim that he is the only person without an agenda (oh yeah, really ...).
The trouble is that in all his examples where he claims the environmental science is bad science that I'm an expert on I find that he's only managed to read (or see) some of the relevant material, he's probably not understood it all, and he's certainly drawn what I regard to be erroneous conclusions. So how then can I trust him on issues where I'm not an expert?
Take for example, the issue of DDT and Malaria, which was introduced both in the speech and the book. The bottom line is that he concludes that the banning of DDT has led to millions of avoidable Malaria deaths. Let's deconstruct his relevant arguments which I think I can summarise as:
The link between DDT use and bird deaths is based only on a correlation (which led to mass hysteria following Rachel Carson's "Silent Spring") and there is no physical link to justify the correlation (aka "We know DDT doesn't cause cancer")
There is a (worldwide) ban on the use of DDT.
There is a correlation between the DDT ban and increase in malaria deaths
Therefore banning DDT was a bad thing.
So, I spent a little bit of time chasing these things down. Eventually, I found this excellent series of blog articles which are a highly recommended read, but I'd already assembled the following:
Let's go back to the points:
DDT is dangerous ...
There is a world-wide ban on DDT use.
Oh no there's not: The twentieth report of the WHO expert committee on Malaria (1998) states:
It is anticipated that for some time to come there will continue to be a role for DDT in combating malaria, particularly in the poorest endemic countries ...
Banning DDT led to a huge rise in Malaria deaths.
Oh really? Leaving aside the ban issue, we have Crichton on the one hand dumping on the use of correlation only arguments (bird deaths without mechanism), but using the same to justify increase in malaria. It seems that the increase in malaria was going to happen anyway. See for example:this, by Shiva and Shiva, which makes two key points:
Major ecological changes have contributed to malaria resurgence. The spread of irrigation projects has been recognised as a major cause for the spread and increase of malaria epidemics. In addition, the expansion of water-intensive crops has created conditions conducive to the spread of malaria.
The morbidity and mortality related to malaria is undoubtedly increasing. Increased dependence on spraying rather than on environmental sanitation (and that too irregular spraying, improper spraying, inappropriate spraying) has resulted not only in increases in the number of vectors but also the emergence of pesticide resistance.
More specifically, Shiva and Shiva say:
Under the continued assault of insecticides, vector mosquitoes have developed resistance, thus undermining the 'insecticidal approach'. During the 1960s, no research was done on the evolution of resistance because of the euphoria of malaria control programmes. This gap in research was filled only after resurgence had occurred. In the case of Anopheles culcifacies resistance to DDT is now common in 18 states and 286 districts, to HCH in 16 states and 233 districts and to malathion in eight states and 71 districts. An stephensi has developed resistance to DDT in 34 districts in seven states and to HCH in 27 districts in six states. Resistance to malathion has been detected in eight districts in three states.
See also Sharma (pdf), which
examines the role of DDT in malaria vector control and argues that DDT-spraying produces diminishing returns and eventually becomes counterproductive.
The ban on DDT was a bad thing.
No ban worldwide. What about in the States? Well, it seems clear that malaria is not a problem there anymore, and the bird populations have recovered. Doesn't seem so bad to me ...
Now obviously I can't speak as to the veracity of any of these references on DDT etc (but I believe the WHO), but it seems that the story is not nearly as simple as Crichton would have it. It is also true that the story is not ever as simple as some evangelestic environmentalists would have it ...
... for my completely unsubstantiated take on this, it's clear that using DDT has worked to eradicate malarial mosquitoes in some places, but it didn't and never could have in some others ... it also happens to be very nasty for some other parts of the ecosystem. The bottom line appears then to be to try and avoid it, but it makes sense to continue to use it where it can make a difference ... that's a much more complicated opinion than "DDT Good" so the science involved in the (non-existent) ban was "Bad".