Zombie DDT Myth Will Not Die

Yes, the DDT ban myth is back, this time in "DDT Returns" by Apoorva Mandavilli that reads like a press release by DDT advocacy group Africa Fighting Malaria. It's in Nature Medicine of all places and is subscription only, but because I'll be quoting the bits that are wrong or misleading you'll see most of it:

After decades of being marginalized as a dangerous pesticide, DDT--short for dichloro-diphenyl-trichloro ethane--is set to be reintroduced into countries that have tried, and failed, to win the fight against malaria.

On 2 May, the United States Agency for International Development (USAID), arguably the most powerful donor agency in the world, endorsed the indoor spraying of DDT for malaria control.

This isn't a change in policy. In November last year USAID said

USAID strongly supports spraying as a preventative measure for malaria and will support the use of DDT when it is scientifically sound and warranted.

But the DDT ban myth peddlers cannot be stopped by mere facts. Mandavilli:

USAID never banned DDT outright, for instance, but nor did it fund DDT's purchase--which amounts to the same thing. For that reason, the May announcement is widely seen as a change in policy even though the agency doesn't position it as such.

USAID can't win. If they say they support DDT use they're lying. If they fund its use then they changed their policy. Nothing they say or do can stop the DDT ban myth.

The World Health Organization (WHO) is set to follow. In its new guidelines, a final version of which is expected to be released later this summer, the WHO is unequivocal in its recommendation of DDT for indoor residual spraying.

Of course, in the old guidelines the WHO was also unequivocal in its recommendation of DDT for indoor residual spraying. They state:

WHO recommends indoor residual spraying of DDT for malaria vector control.

Later in the article Mandavilli even mentions this fact:

The WHO recommends 12 insecticides including DDT--which is an organochlorine--six pyrethroids, three organophosphates and two carbamates.

But the DDT ban myth is immune to mere contradictions.

Mandavilli continues:

For these impoverished countries, the choice may seem clear: DDT is cheap and lasts longer than other pesticides, so it has to be sprayed less often. Most pesticides work by killing mosquitoes on contact, but DDT also repels them.

"DDT is the most effective chemical, the most effective insecticide in terms of malaria," says Arata Kochi, director of the WHO's Global Malaria Programme.

That's rather an oversimplification, according to the
latest publication from ... WHO's Global Malaria Programme.

However, the success of IRS depends largely on the mosquitoes resting
indoors before or after feeding -- not all species do this naturally
and the excito-repellency of DDT and pyrethroids may dissuade
mosquitoes from resting long on sprayed surfaces. Other requirements
include the need that human shelters have walls to be sprayed, access
to the interior of all houses, and a relatively stable human
population without a high frequency of replastering of sprayable
surfaces. The conditions for "eradication" were not met in all malaria
areas, especially in Africa, where serious efforts were never mounted.

So the repellency effect of DDT makes it less effective. And in Africa DDT is not so much returning, but being used seriously for the first time. The WHO report goes on at length on the different methods of vector control. There isn't one best method. It depends on the vector, infrastructure support, nature of dwellings, insecticide resistance and on and on. Here's a taste:

In areas where malaria vectors are fully susceptible to pyrethroids, sideby-side comparison of the same pyrethroid used for both methods against
malaria transmitted by An. gambiae s.s. and An. funestus showed very similar
impact on the entomological inoculation rate (EIR) of the vector population,
incidence of malaria infection and malaria morbidity in children. A review
of the remarkable results achieved in the 1950s, 1960s and 1970s with IRS
in highly endemic areas of Africa shows that so far none of the recent ITN
trials has done as well. However, IRS programmes were larger in scale than
the relatively smaller ITN efficacy trials, so the comparison conflates two
methods and scales of intervention.

Cost comparisons of IRS and ITNs yielded surprisingly variable results.
The encouraging past results with IRS in tropical Africa did not lead to
nationwide campaigns. It can be argued that this has been because in
very low income countries it is not possible routinely to meet the logistical
demands of ensuring that trained spray teams equipped with working
spray pumps and sufficient insecticide arrive at each village in time to spray
before the malaria season. It can also be argued that it is more feasible to
supply ITNs in such circumstances because this does not impose similar
logistics requirements.

Moreover, the experience of long-term use of IRS by organized antimalaria
campaigns in many parts of the world has frequently shown a progressive
development of people's fatigue and reluctance to allow intrusion into
their homes. This phenomenon may be less likely to occur with the use
of ITNs, which are far more under the control of households. In contrast,
in rapid response to epidemics there are good reasons to favour a trained
and equipped IRS "fire brigade" capable of moving quickly to an area
where there is a high likelihood of a malaria epidemic unless quick action
is taken.

Mandavilli then goes in for the traditional Rachel-Carson-worse-than-Hitler gambit.

Between 1955 and 1969, the Global Malaria Eradication Campaign also relied heavily on DDT. In Europe, India, South America, Africa, wherever it was used widely, DDT cut malaria rates dramatically and saved millions of lives.

Then came Carson's Silent Spring-- credited with launching the environmental movement--which famously described DDT's horrific effects on the food chain, and the stark silence left behind by dying birds. The book was so effective that to this day, any mention of DDT instantly evokes images of bald eagles and thinning eggshells.

DDT soon became a symbol of Western governments' rash embrace of science. In the US and in Europe, environmental groups waged a successful campaign against the pesticide. Based largely on its effect on the environment--and on public opinion--the US Environmental Protection Agency in 1972 banned DDT. Norway and Sweden had begun the trend in 1970, and the UK signed on in 1986.

Environmental groups that still oppose DDT see its use in developing countries as a double standard. On the other hand, note champions of DDT, most of those groups are based in countries where malaria is only a distant memory.

"I think the whole push of the environmentalists like Rachel Carson and many others to eliminate all uses of DDT are, quite honestly, responsible for millions and millions and millions of human deaths," says Don Roberts, professor of tropical public health at the Uniformed Services University of the Health Sciences in Maryland.

This misrepresents Carson. She opposed the indiscriminate use of DDT and warned that overuse would cause insect resistance and make it useless. The restrictions on the agricultural use of DDT that she helped inspire have prevented the development of resistance and are the reason why it can still be used today in many places to fight malaria. In short, she prevented many deaths from malaria.

And who are these environmental groups that oppose DDT use? Neither Greenpeace nor the World Wildlife Fund oppose its use.

Mandavilli continues

Most African nations are heavily dependent on foreign aid and can ill afford to cross a line drawn by donor agencies.

The World Bank went one step further, making the ban of DDT a condition for loans.

Far from banning DDT, the World Bank
funds DDT in Eritrea, India, Madagascar and the Solomon Islands.

The WHO supported the use of bednets dipped in insecticide over indoor spraying, even though malaria rates continued to increase.

Yes, they support bed net use because there is a mountain of evidence showing that bednets are effective. See the WHO report linked above. This sort of reporting is pernicious, because it misleads readers into thinking that bednets don't work.

"People are very emotional about DDT, even within the WHO," Kochi says, adding that much of the reaction to DDT was a response to political pressure.

Yeah, no kidding. The Rachel-Carson-worse-than-Hitler brigade want to exploit the issue to bash environmentalists. Hence the weird focus on DDT. You'd think that anti-malarial drugs, other insecticides and other means of vector control don't exist.

Usually these sorts of pro DDT articles ignore resistance, so I should note that Mandavilli at least mentions it:

Unless done well, however, using DDT may be dangerous--and powerless against malaria.

For spraying to be effective, at least 80% of the affected area must be covered. Global agencies must first map the distribution and behavior of different kinds of mosquitoes and, most important, patterns of resistance to insecticides. "The last thing you want to do is select for resistance," says Coetzee.

Hey yeah, that's what Rachel Carson was saying...


More like this

I seem to remember seeing some dose-response curves for resistant bugs (tobacco hornworms?) from the early 1970s that showed by the end of the 1960s it took more than a gram of DDT to kill a gram of hornworm. In other words, you had to drown them in it. That's one of the bits that never seems to make it into these anti-enviro screeds.

By justawriter (not verified) on 01 Aug 2006 #permalink

Good point, justawriter! I didn't find the hornworm dose-response curve, but did find material for a useful trivia question or two to pose to the DDT fans when this issue comes up:

Q: Of 39 Anopheles mosquito species considered to be important malaria vectors, how many are now reported to be resistant to DDT?

A: 30.

Q: How many African malaria vectors are resistant to DDT?

A: All of them.

Remember that quinones confer resistance to the Plasmodium thingy that is the bad thingy that makes people sick.

Some shills "forget" to mention that little bit.



This website gives some info on Mandavilli and includes her e-mail address: http://www.nature.com/nm/about/about_eds/index.html

She sounds like a reasonable person from the description given there. Perhaps it would be worth e-mailing her pointing out the misstatements in her story (or maybe even giving her the link here)? This seems to be one issue where someone who is not well-informed on the subject can easily be led astray by people like Roberts with axes to grind who are pretty good at passing themselves off as unbiased authorities.

By Joel Shore (not verified) on 01 Aug 2006 #permalink

...Perhaps it would also make an impression with her if you pointed out that one of the seminal papers on the growth of DDT resistance with its overuse in agriculture appeared in the parent magazine of her employer. [I am referring to G. Chapin R. Wasserstrom, "Agricultural production and malaria resurgence in Central America and India", Nature, Vol. 293, pp. 181-185 (1981), which I believe you might have blogged about before.]

By Joel Shore (not verified) on 01 Aug 2006 #permalink

The ABC have been reporting this here. Also I heard it on news radio this morning.

Tim, you seem to be all over the place in this posting.

Do you support the use of DDT (indoor spraying) for malaria control in Africa or not?

Yes or no will do.

In other words, you had to drown them in it. That's one of the bits that never seems to make it into these anti-enviro screeds.

Do you support the use of DDT (indoor spraying) for malaria control in Africa or not?

Yes or no will do.

James, I won't presume to answer for Tim, but I will suggest that you could find the answer to that question fairly easily here.

To choose but one example,

You can tell the deeply ignorant pro-DDT articles because the authors don't mention or even seem aware that mosquitoes evolve resistance to insecticides. DDT's persistence is only an advantage when it sprayed indoors and it stays where it is sprayed. Persistence is a big disadvantage when spraying outdoors because the insecticide is rapidly diluted and the mosquitoes get exposed to sublethal doses. This is perhaps the best method know for breeding insecticide resistant mosquitoes. That is why DDT is only used for indoor residual spraying, these days.

James, I believe that DDT should be used for IRS **in rotation with other pesticides** so as to prevent the development of resistance.

The trouble with this strategy is that every time you rotate DDT out the Africa Fighting Malaria crew will scream "EVIL BABY-KILLING CARSON WORSHIPPERS BANNED DDT!!!!!!!!!". And then when you rotate it back in Nature Medicine will publish a clueless article about DDT is coming back. Lather, rinse, repeat.

I'm definitely not an expert.. but I took a really interesting malariology class in grad school and am dying to join this debate!
In response to jre: mosquitoes can definitely develop resistance to DDT, but a little known fact is that this resistance is not permanent. So although these countries may be home to 30 species of mosquito that have been known to develop resistance to DDT, it's been so long since DDT was actually used in many of these places... present resistance is not actually a big obstacle, or a reason to not use DDT.
I also want to address the comment.. "Hence the weird focus on DDT. You'd think that anti-malarial drugs, other insecticides and other means of vector control don't exist."
Personally, I think that we don't hear enough about DDT. Yes there are other ways of preventing malaria... but millions of people, mostly children, still die of malaria every year, and we are not using all the tools we have to stop it, simply because of politics, semantics, etc.

Megan -
You might (or might not) be surprised to know how much I agree with you. It sounds as if you are asking exactly the right question, viz.: Given everything we know about the disease, its vectors, and the tools available, what is the most effective strategy for fighting malaria?It bears noting that our esteemed host took exactly that approach, just one comment up. Resistance to a given insecticide in a given species is neither absolute (in which case there's no point in any use of that agent) nor, as you've noted, that resistance is permanent (in which case we need never change our strategy). I would expect (and would like to know if I'm wrong) that, in your malariology class, the history of DDT resistance in Anopheles was discussed. As you probably know, there was enormous enthusiasm for DDT as a weapon against malaria in the late 1940s and 1950s. International public health organizations, with the predecessor to WHO in the forefront, sprayed DDT on every skeeter in sight -- that is, until DDT resistance, starting with Anopheles sacharovi in Greece, slugged them in the gut. That experience was an enormous shock to those who had thought that total victory over malaria was just around the corner. Now, sixty or so years later, the emotional impact of that disappointment is largely forgotten. A superb historical account may be found in Gordon Harrison's Mosquitoes, Malaria and Man: A History of the Hostilities Since 1880.
So -- after it got a bucket of ice water in the face, did WHO abandon DDT as a weapon against Anopheles?

Absolutely not.

Try this experiment: go to WHO's web site, and do a search for "DDT." The very first hit is for a very pragmatic document listing DDT as an essential element in malaria control, but stressing the need to limit its use, for example

Although DDT has been banned from agricultural use in most countries since the 1970s due to its damaging effects on the environment, it continues to be used in limited quantities for public health purposes. For many malaria-affected countries, responsible DDT use is a vital strategy for preventing malaria transmission and controlling epidemics. Countries continue to use DDT primarily because they cannot afford reliable alternatives or do not have the capacity to develop them.

This is the same theme sounded by public health authorities everywhere malaria is prevalent: Use DDT when necessary, use it in targeted applications (such as indoor residual spraying) where it does the most good, and avoid its use where it will damage the environment and lead to increased resistance. Use other pesticides in rotation, and adjust your strategy as new information comes in.

It cannot help but be annoying when that strategy -- the very best available, given our knowledge -- is criticized as having caused millions of unnecessary deaths. It is a false accusation, and ignorant, and oily and smug, and allied with a host of egregious causes, and ... oh, just let me catch my breath.


James, I believe that DDT should be used for IRS in rotation with other pesticides so as to prevent the development of resistance.

That sounds reasonable. Is that, in practice, what has been done over the past 40 years?

James, now you're walking slowly backwards.

The screed meme continues to be propagated by think tank "experts" who are funded by wealthy right wing idealists. It easily propagates among those who need to see the world in black and white or who need a scapegoat for every difficult problem.

The other factor is an uncritical print media, fed by novice writers who lack critical thinking skills, the experience of age, and curiosity about the natural world. I blame the mindless state of journalism on the "Communcations Degree": all about form and nothing about function.

By John laumer (not verified) on 03 Aug 2006 #permalink

John - who are these "wealthy right wing idealists"? Idealism tends to belong to the Left, along with Unaccountability. Also, the list of wealthy left wing idealists would be just as long. Or short.

Recent events have shown that Tim has stepped on his old feller somewhat on this one. He is falling back on the resistance argument but last time I checked didn't DDT act as a deterrent even to resistant mosquitoes?

By Jack Lacton (not verified) on 03 Aug 2006 #permalink


Tim has been advocatign the use of DDT for IRS as logn as I've been reading his psots on the topic.

The point is - DDT is not a panacea.

Besides simply being untrue and slanderous, the real danger of the DDT Ban myth is that it may distort spending priorities in combatting malaria.

Broad-acre DDT spraying is relatively expensive and maximises the risk of resistance developing.

It is also infeasible in some parts of Africa because of the lack of an effective government infrastructure to conduct the spraying.

IRS sprayign with DDT is effective in many situations- but rotating DDT with other insecticides reduces the emrgence of resistance. (I'm also curious as to why you think mosquitoes can develop immunity to the toxic effects of DDT but not its repellant effect.)

As Tim noted in his first post, IRS can be ineffective in soem situations. For example, in soem developing coutnries people replaster their walls annually with mud to reinforce the strength of adobe walls. This means IRS has to be doen more frequently.

In these circumstances (and where governemnt services can't operate) netting is a potentially more effective strategy.

So my reading of Tim's comments is that we need to get beyond fetishising DDT as THE SOLUTION (even if it means you can no longer accuse your political opponents as worse than Hitler), use it where it's effective and recognise that the only way to significsntly reduce the death toll from malaria is a combined strategy of vector control (using DDT where appropriate); netting; and treatment combined with additional research into vaccines and other forms of treatment.

By Ian Gould (not verified) on 03 Aug 2006 #permalink

James, now you're walking slowly backwards.

Barry, I wasn't trying to make a point, I was asking a genuine question. Tim supports use of DDT for IRS in rotation with other pesticides. I'm asking if this is a strategy used in the past, and I might add to that question, is it being used now?

James, my reading of the evidence is that very few poor countries have put together the kind of organisational structure required for systematic rotation of pesticides (richer countries can afford not to use DDT at all).

Instead what you have is unsystematic rotation - one pesticide is used for a while, resistance emerges, and another is tried. Or maybe funding runs out and nothing is done for a while. These organisational problems are one reason why a lot of organisations prefer bednets, which can be adopted on a household by household basis.

By John Quiggin (not verified) on 03 Aug 2006 #permalink

John, thanks for your comment.

I preface my remarks by noting that I'm not being adversarial (as an earlier commenter seemed to think).

I'm puzzled as to why systematic approaches are not being applied to the malaria problem, seeing how the science seems to be settled. Why do the UN and WHO seem to be sitting on their hands? If there are organisational problems, why don't these organisations solve these problems? Isn't that their job?

It seems to me a cop out to say "well, it's all too hard, so we'll recommend bednets".

I recall reading a New Yorker article about DDT and malaria that recounted huge benefits reaped by a systematic implementation of IRS of DDT in (I think) the late 1950s, early 1960s.

I apologise for not giving a cite, but my brother has the "complete NY archive", so I'll see if he can find it and report back.

Thanks, jre, that's the article I was thinking of.

well, nobody asked me but
I am AGAINST rightwing assholes telling me there is and/or has been a "DDT Ban", due to the allpowerful and wealthy environmentalist cabal which controls the world.
And I am AGAINST wellmeaning (or not) dupes switching the argument to "well then are you for or against DDT spraying?" whenever the above statement proves false.

According to Tom Bethell's excellent book on science, even Ralph Nader supports reintroducing DDT, in a controlled and limited way. Mr. Bethell also notes that major newspapers have editorialized that this needs to be done.

Perhaps we should listen to the liberals and conservatives who are concerned about the harm that banning DDT has had on large numbers of innocent people.

"According to Tom Bethell's excellent book on science, even Ralph Nader supports reintroducing DDT,"

How do you "reintroduce" something that's been in continuous use?

By Ian Gould (not verified) on 06 Aug 2006 #permalink