In a recent post I observed that the Junk Central Station crew were ignorantly advocating the use of DDT in Sri Lanka after the tsunami, apparently unaware that mosquitoes in Sri Lanka were resistant to DDT. The World Health Organization’s plan for malaria prevention in the wake of the tsunami advised against using DDT because:
Endemic sporadic malaria close to the affected areas transmitted by An.culicifacies, which has been considered DDT-resistant for many years, but is still sensitive to organophosphates, such as malathion, and pyrethroids.
One alarming new difference [in Galle, Sri Lanka] is that malaria is back, and is poised to strike down still more of the children, many orphaned, of this wretched place. It can be stopped, but only if ill-informed prejudice against DDT, the insecticide, is dropped. …
the malaria-control program is being compromised by outdated thinking, especially from the world’s leading health and government-aid agencies.
The prime example of their folly is found in a paper, “Malaria Risk and Malaria Control in Asian Countries Affected by the Tsunami,” in which the World Health Organization (WHO) outlines its policy for the affected region.
Historically, the primary method of malaria control has been Indoor Residual Spraying (IRS)—the spraying of house walls with tiny amounts of an insecticide, usually DDT. IRS often kills mosquitoes, but more important, it creates a barrier between man and mosquito. Studies show the vast majority of mosquitoes won’t enter a DDT-sprayed building, and this chemical barrier prevents transmission of the disease, much as prophylactic drugs or bed nets do, but more cheaply. Such an approach was highly successful in Sri Lanka. Owing to DDT, malaria rates fell from three million cases a year in the 1940s to fewer than 50 in 1963.
But then environmental pressures against DDT led to its abandonment, first in Western countries and then in most other parts of the world. …
Studies showed that Sri Lankan mosquitoes may be developing resistance to DDT, which meant that some of them would not be killed by the insecticide. Even the WHO report says Sri Lanka’s malaria vectors have been considered DDT-resistant for many years. But DDT’s main role is as a repellent, not as a toxic agent. Houses sprayed with DDT repel far more mosquitoes than any other insecticide tested and so remain effective even when resistance is substantial. This information, although known by health entomologists, is ignored by the WHO, which has adopted the anti-DDT environmentalist agenda. The WHO advises using alternative insecticides—although the organization buys precious few even of these.
So that’s Bate’s story. How does it compare with the facts?
“WHO … has adopted the anti-DDT environmentalist agenda”
Here is a letter from WHO’s Allan Schapira in response to similar claims:
Nature 432, 439 (25 November 2004);
DDT still has a role in the fight against malaria
Sir — Your News story about the Roll Back Malaria campaign (“Struggling to make an impact” Nature 430, 935; 2004) quotes me as claiming that pressure from government and other donors made spraying difficult to push through politically. I am also quoted as saying: “We have had very, very strong lobbying over DDT. We have had to give up.” The quotations give the impression that the World Health Organization (WHO) has given up on DDT under the pressure of lobbying. I believe this is misleading.
When interviewed, I explained that we sometimes had to give up trying to convince a specific donor to financially support indoor spraying with DDT, if they flatly refused because of its perceived toxicity and ecological hazard. This has occasionally occurred in countries where the government wished to use DDT, and there was evidence that it was the best option for malaria-vector control.
However, in general terms, the WHO has never given up in its efforts to ensure access to DDT where it is needed. At meetings of the intergovernmental negotiation committee on the Stockholm Convention—which seeks to control the spread of persistent organic pollutants—the WHO has successfully defended the right of countries to use DDT for disease-vector control, if no suitable alternative can be found. The WHO also supports worldwide efforts to develop alternative products and phase in alternative control strategies (link).
The Stockholm Convention came into force in May this year. Its exemption allowing restricted and controlled use of DDT according to WHO guidelines is a good example of appropriate international regulation on a difficult dilemma. It is not a compromise but a solution, which ensures that disease-control programmes maintain access to a useful product, while fully respecting the need to prevent environmental damage from persistent organic pollutants, such as DDT.
Strategy and Policy Team,
Roll Back Malaria Department,
World Health Organization,
“WHO advises using alternative insecticides”
From the WHO’s FAQ on DDT:
WHO recommends indoor residual spraying of DDT for malaria vector control.
Bate’s statement is a sort of half-truth because the WHO does recommend alternatives depending on the local circumstances:
Indoor residual application of DDT may have very little impact, for instance, if the malaria vector tends to rest and bite outdoors, and does not enter houses.
Information on vector susceptibility and tolerance to DDT should be up-to-date and backed up by an effective pesticide resistance management strategy to ensure continuing pesticide effectiveness. Local vector resistance or increased tolerance to DDT may affect its overall effectiveness.
This is why they don’t recommend DDT in Sri Lanka.
“Studies showed that Sri Lankan mosquitoes may be developing resistance to DDT”
Pinikahana and Dixon, Trends in malaria morbidity and mortality in Sri Lanka. (Indian J Malariology):
After the discovery of DDT resistance in 1969, malathion spraying took over in 1973, and USAID-assisted control programme, involving case-detection and treatment, started in 1977.
This is not “may be developing resistance”. They have developed resistance, and it was way back in 1969.
“Houses sprayed with DDT repel far more mosquitoes than any other insecticide tested and so remain effective even when resistance is substantial”
India has been using DDT against malaria continuously since the 1940’s. V.P. Sharma, DDT: The Fallen Angel (Current Science 85 1532-1537) explains why it is becoming ineffective:
The Health Department of Maharashtra reported an increasing trend of malaria even after two rounds of DDT indoor spraying between 1995 and 1997, with a 75-83% coverage of rooms in houses. Monitoring in 74 villages revealed that malaria transmission continued, and cases had sharply increased by the third quarter of 1997. In November 1997, a special spraying round with Lambda-cyhalothrin (10% WP) managed to interrupt malaria transmission …
The declining effectiveness of DDT is a result of several factors which frequently operate in tandem. The first and the most important factor is vector resistance to DDT. All populations of the main vector, An. culicifacies have become resistant to DDT. The excito-repellent effect of DDT, often reported useful in other countries, actually promotes outdoor transmission …
Third, DDT, cheaper by weight than alternative pesticides and manufactured indigenously by government-controlled HIL, is sprayed with the false belief that its excito-repellent action prevents transmission.
In India at least, it seems that the “outdated thinking” belongs to those who continue to use DDT even though it has lost effectiveness.
“[Malaria in Galle] can be stopped only if ill-informed prejudice against DDT is dropped.”
Olivier Briet et al have just published a study on malaria in Sri Lanka after the tsunami (Malaria Journal 2005 4:8). They write:
DDT and Malathion are no longer recommended since An. culicifacies and An. subpictus has been found resistant.
Figure 2 in their paper shows that since 2000, malaria incidence has been reduced by a factor of 100 without any use of DDT. Figures 3 and 4 show that Galle has been free of malaria for years.
“[That DDT is effective despite resistance is] known by health entomologists”
I asked Olivier Briet, lead author of the Sri Lanka malaria study I just cited. He allowed that it might be true, but he was unaware of any study supporting Bate’s claim, especially in relation to Sri Lanka.
“[Spraying DDT] prevents transmission of the disease, much as prophylactic drugs or bed nets do, but more cheaply”
Bhatia et al conducted experiments in India to see whether indoor spraying or bed nets were more effective. They found that bed nets were more effective at preventing malaria and were more cost effective as well. Because of DDT resistance they sprayed with deltamethrin rather than DDT, which would have been even less effective. Bed nets were also found to be more cost effective in Sri Lanka.
DDT spraying may well be effective in other places, but it does not seem necessary or at all likely to be effective in Sri Lanka. As a supposed expert on malaria, Bate should be aware of these facts.
So who is Roger Bate, anyway? Well, apart from being an economist at the American Enterprise Institute, he is a director of the astroturf operation Africans Fighting Malaria. He writes frequently for Tech Central Station. He is an adjunct fellow of the Competitive Enterprise Institute. He was a cofounder of European Science and Environment Forum (ESEF), which was another astroturf operation, secretly funded by Philip Morris to push a pro-tobacco agenda. ESEF was the European version of The Advancement of Sound Science Coalition (TASSC), so I guess that makes Bate the European version of Steve Milloy.