Response on Malaria and DDT-BECKER

Thanks for some informative comments. Clearly, I should have said the WHO rather than the WTO. I apologize for this carelessness that is especially disturbing to me since I often write about the WTO. I also regret that I probably exaggerated how many lives could have been saved over the years by extensive use of DDT spraying in houses. However, I am not guilty of saying that DDT spraying alone would do the job, for I did say that mosquito nets and drugs are also useful. A combination is the best approach, but these other methods are just not a good enough substitute for DDT spraying. So I do stand behind a claim that opposition to DDT spraying by many organizations caused a very large number of needless deaths from malaria. Does the recent WHO statements supporting the use of DDT in homes reflect a change in attitudes toward DDT home use by this organization? One strong critic of my discussion points out several errors in what I said, and I am indebted to him for these corrections. However, he is inconsistent on this issue of whether the WHO has "changed" its position. On the one hand, he says that "The WHO…has always supported its use" (that is, DDT spraying), but then quotes with approval a statement by another critic of DDT spraying that "The World Health Organization's new (!) stance on DDT" (my parenthesis). "New" or not new, that is the question? I was wrong to say that the WHO had banned the use of DDT in homes until recently. However, it is accurate to say I believe that the WHO had not strongly endorsed its use until a few weeks ago, and that many donor agencies were for this reason reluctant to finance purchases of DDT for household spraying. One commenter challenged me (and his challenge was very well answered by another commenter) as to whether DDT house spraying does pass a relevant benefit-cost criterion. Accepting his assumptions, DDT spraying would cost $12 per year per person. That amount seems to be a highly worthwhile expenditure if we relate it to estimates of the value of saving the lives of young persons even in very poor countries. Of course, a full analysis would require knowing the money value placed on their utility by people in poor countries (my paper with Rodrigo Soares and Tomas Philipson in the March 2005 issue of the American Economic Review on declines in mortality in poor countries tries to measure utility value of improved life expectancy, not improvements in GDP alone), the probabilities that such spraying would save lives or significantly improve the quality of lives, the productivity of alternative uses of these funds, such as to find an effective vaccine, and so forth. I, have not, nor has any one else to my knowledge, made these calculations, but if spraying only costs $12 per year, and it is effective in significantly cutting deaths from malaria (some commenters dispute that), to me that seems like a great use of private or public funds.

Comments

[owinok]

The application of DDT in combination with other forms of vector control is imperative in saving lives in the future but it is highly unlikely that the malaria mosquito can be led to extinction. The correct approach ought to be the reduction in the number of mosquitoes to such a level that there is a break in transmission of the parasite. The pursuit of the extinction of mosquito may be tempting as a decisive solution but the odds are that it is virtually unattainable.

[Robert Chung]

1. Although sterile insect techniques (SIT) can be a very useful tool in controlling certain types of pests, they never lead to complete extinction.

2. There are four different malaria parasites with vastly different lethalities -- the type of malaria endemic in Sub-Saharan Africa is deadliest to chldren under the age of five but actually doesn't kill many adults (though it makes them quite sick, and repeatedly). This is not to deny the tremendous human toll of the disease; it is only to point out that it is hard to say exactly how many lives are lost (or saved) without specifying exactly which strain of parasite one is discussing.

3. A reasonable estimate of the material cost of IRS (interior residual spraying) vs. LLN (long-lasting insecticide treated nets) was included in a relatively recent Ugandan Ministry of Health report. That report estimated the 6-month material cost of DDT at around $2 per household, while the cost of a LLN (which lasts about 4 to 5 years) was about $6. IRS needs to be repeated every 6 months, and the cited cost is only for the insecticide itself and does not include the cost of spraying. It is generally acknowledged that the logistical cost of arranging an army of sprayers who can visit an area twice a year is considerable. The distribution cost of a LLN is quite a bit lower: basically, an entire truckload of LLNs can be delivered by one man while that same man with a sprayer can cover about eight dwellings per day. IRS can be especially effective when malaria is episodic and short-term protection (for, say, one season) is needed in order to "break" an epidemic. WHO has always supported this particular use of IRS. In Africa, LLNs work especially well because even one net in a household can be targeted to the children under age five.

[Jose Costa]

When it's malaria, it's Africa! So we better leave these old fashion approaches. We will never solve the African problem with DDT or even a vaccine without a political change in Africa. I am from Angola and there they say malaria is a problem of urbanism! In fact, those who live in "slum villages" are more likely to get ill than those who live in better places. Personally i believe DDT could solve part of the problem, but better governance is the key, because malaria is really simple to be treated and avoided.

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