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The science and politics of DDT

September 18th, 2006

Arguments about DDT have been going on for a long time in the blogosphere and similar circles. These debates typically involve a confusion between two unrelated issues
* The bogus story, popular in rightwing circles, in which the US ban on agricultural use of DDT, inspired by Rachel Carson, is morphed into a global ban on DDT, bringing to an end a previously successful compaign to eradicate malaria
* The real disputes, among malaria experts, about the relative merits of insecticide-treated bednets and spraying of house walls, and of DDT and alternative insecticides.

Now the two have coincided in the real world, with effects that may or may not be good. WHO recently appointed Arata Kochi as head of its malaria program. Kochi, who previously worked on the Stop TB initiative, has a reputation as a headkicker, but also as someone who gets things done. It’s worth noting that, while this kind of reputation is sometimes well-earned, there are often cases where the supposed accomplishments turn out be ephemeral or non-existent (remember ‘Chainsaw Al’ Dunlap, for example?).

Kochi has decided to shake up the ‘malaria community’ and an obvious line of attack is to line up with those among its critics who favor a bigger role for DDT. He’s just made a big announcement of a shift in favor of DDT, coinciding with the resignation of the WHO’s leading expert on insecticide spraying.

Reading the announcement and the NYT closely, the change in reality is much less than in rhetoric. Of the 17 African countries that now use interior spraying, 10 already use DDT, and it will almost certainly turn out that some of those who don’t have good reasons for choosing other pesticides (resistance, or harm to helpful insects that prey on pests in roofs for example).

And the substantive change in WHO guidance is much less dramatic than the rhetoric would suggest. WHO is now recommending the use of indoor residual spraying (IRS) not only in epidemic areas [as in the past] but also in areas with constant and high malaria transmission, including throughout Africa.

It’s far from clear that the change is backed up by a scientific analysis of the relative cost-effectiveness of the options. But, as with all the fads and fashions in areas like this, cost-effectiveness is not necessarily the most relevant criterion. The US appears willing to put in a substantial amount of extra money, and the US wants to push DDT. So, it’s probably better to please the donors, than make a stand on the science and risk losing the money.

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  1. taust
    September 18th, 2006 at 20:59 | #1

    John;
    I stand in awe of the skills of a professor. I have had two or three attempts at getting to a position on DDT that I felt intellectually comfortable with and failed each time. Your example gives me heart that a bottom does exist I will make the attempt again.

    Howeve give Gore’s current activities I could not resist sharing this with you:

    Vice-President Albert Gore suggests one answer in his introduction to the 1994 reissue of Silent Spring, a book often cited as the founding text of contemporary environmentalism. Before Carson’s book, he writes, “There was virtually no public dialogue about the growing, invisible dangers of DDT and other pesticides and chemicals.” The fears that have come down the decades from Rachel Carson are summarized in the WWF Core Issues Statement, which claims that “even small quantities of …POPs can wreak havoc in human and animal tissue, causing nervous system damage, disease of the immune system, reproductive and developmental disorders, and cancers.

    as they say in the caffe latte policy elite enjoy.

  2. Bob Sutherst
    September 19th, 2006 at 08:30 | #2

    John,
    Support for DDT came early from Brian Sharp in Durban, S Africa, simply because they had an outbreak of malaria that was causing 40,000 deaths a year. DDT was a quick and effective way to reduce those losses. Other approaches (eg Bt) are being investigated in parallel with internal house spraying that has been shown to cause a very small incidence of human health problems – from memory related to the very young. There was no international pressure to use DDT, indeed the opposite was the case.
    Bob

  3. September 19th, 2006 at 14:17 | #3

    Bob, you are mistaken. There was an outbreak with 40,000 cases (not deaths) in South Africa. Partially switching back to DDT was one of the measures taken, but they also switched medicines as well. More here.

  4. Pinguthepenguin
    September 19th, 2006 at 23:58 | #4

    Tim, you may also want to set this guy straight…
    http://graemebird.wordpress.com/

  5. Bob Sutherst
    September 20th, 2006 at 10:33 | #5

    Oops, thanks Tim, cases not deaths. Yes, they used other drugs as well but we are talking about DDT reducing the losses (not solely) here. It does not change my argument that the switch to DDT was based on rational costing of the options, and the decision making was made in the absence of a push from the USA, which is what John was questioning. Perhaps the US came on board later John?

  6. September 20th, 2006 at 12:42 | #6

    Bob, IRS was already recommended by the WHO in South Africa. The new policy adds a bunch of countries in Africa where the malaria problem is worse. There is no scientific support for a change in policy in those places, and the new policy talks about gathering evidence in this area.

  7. jquiggin
    September 20th, 2006 at 13:18 | #7

    Bob, there’s been increasing pro-DDT pressure from the US right over the last 5 to 10 years, largely aimed at attacking Rachel Carson and the green movement over the ban on agricultural use of DDT (which was actually beneficial, in slowing the development of resistance). This has only been reflected in official US policy in the last few years.

  8. September 20th, 2006 at 15:53 | #8

    PrQ,
    I was listening to the ABC a couple of days ago, after the WHO decision was announced. One of the commentators, from the US, said that there is simply no evidence the DDT is, in any way, harmful to people. Is this the case and, if not, can you link to some evidence?

  9. derrida derider
    September 22nd, 2006 at 15:31 | #9

    I don’t think any serious researcher has ever claimed that DDT is more hazardous to human health than the alternatives – the campaign to ban DDT in the early 70s on these grounds was quite dishonest (although the ecological arguments were slightly less specious and as John points out the ban had a silver lining anyway). In humans the lethal dose for aspirin is lower than that for DDT.

    But yeah, now it’s the Right that’s being deeply dishonest.

  10. September 22nd, 2006 at 15:51 | #10

    Derrida, the campaign in the early 70′s was based on the damage that DDT was doing to birds specifically ones like the pregrine falcon and the bald eagle.

    Perhaps you are confusing the campaign against DDT use with similar campaigns to ban Dieldrin and Heptachlor for instance. Or perhaps you are just being ‘deeply dishonest’, it’s quite fashionable really.

  11. derrida derider
    September 24th, 2006 at 20:11 | #11

    Oh bullsh*t, kyangadac. I was there and involved in the issue at the time (I was doing a biology degree and I was politically active on the left as well). There were *plenty* of suggestions by the nascent green groups that it was human health that was the issue. And read “silent Spring” again.

    Ecological arguments did not then resonate sufficiently with the public to defeat the agricultural lobbies, but health ones did and do. Usually it was along the lines of the old “but we cannot prove DDT has no long term health effects” (sound familiar? “We cannot prove x has no long term effects” is a politically effective argument for many values of x. It’s awfully hard to prove a negative, especially long run ones).

    And IIRC the egg shell issue turned out to be something of a bum rap anyway. You need a lot more insecticide than even top predators accumulate to interfere with calcium metabolism (OTOH at the time I thought the effect on freshwater fish was underrated).

  12. Bob Sutherst
    September 26th, 2006 at 10:22 | #12

    One concern with the reintroduction of DDT for house-spraying to help control malaria was the risk of the chemical being diverted (read stolen) and used on crops close to water and so entering the foodchain. Another was the fear of accelerating selection for resistance by exposing field populations of mosquitoes to selection as John eluded to. I thought DDT was dropped from some malaria campaigns when resistance led to epidemics of disease in people with diminished immunity due to lack of continuous exposure to infection while DDT was being used effectively.

    I think the decline of immunity of the human populaiton during successful malaria programmes is one of the greatest challenges we face because permanent eradiction is a pipedream in the developing world. It suggests that one should be aiming for a low-level trickle infection with good public health responses to minimize clinical effects. But then we have recurring resistance to the succession of drugs ans social upheavels as well. No wonder malaria is seen as being intractable in many quarters. But, I digress from the DDT issue. sorry.

    These risks need to be factored into any analysis of costs and benefits.

  13. September 29th, 2006 at 09:59 | #13

    Sometimes the reason for things happening is simpler than you think. Internal politics is always one of the rugs to check under.

  14. Andrew Taylor
    September 29th, 2006 at 10:41 | #14

    Eggshell-thinning isn’t a “bum-rap”. Theis review is a good starting point if you want to trawl through the evidence: Lundholm CE. 1997. DDE-induced eggshell thinning in birds: Effects of p,p’-DDE on the calcium and prostaglandin metabolism of the eggshell gland. Comp Biochem Physiol 118C(2):113-128. Or any Ornithology text will have an overview.

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