DDT, Junk Science, Malaria, and the attack on Rachel Carson
Some crazy claims have been made lately about Rachel Carson. How wacky are the claims?
Well, this wignut says Rachel Carson is on a level with Hitler, Stalin, and Pol Pot. Here’s another one, who also adds that “massive testing has documented that synthetic pesticides are no cancer threat to humans.”
Wow. Just…wow.
Think this is a fringe issue? You can also read this stuff in the New York Times, Washington Times, and CBS news.
I’ve been looking at this fight for a couple of weeks now; circling around the problem, and trying to figure out where to start. One of the top pages when you search on Google for either Malaria or DDT is Junk Science–a page that claims to “debunk” the DDT ban, claiming it’s “A Green Eco-Imperialist Legacy of Death.”
I’m going to examine their claims, since they seem to be the ringleaders. Their site is having intermittent server problems, so I’ll add a Fox News story written by one of the Junk Science “experts,” since it’s more likely to remain in a stable state.
What are the Claims?
The key claims I see repeated most often by JunkScience and DDT apologists are:
1. Banning DDT in the past caused the deaths of millions of people from malaria. (“environmental activists subsequently exported the ban to the rest of the world – with horrific consequences, including tens of millions killed and billions made ill by malaria over time” (Fox News)
2. DDT spraying now will save millions of people in the 3rd world from malaria (“anti-malarial use of DDT allows more healthy populations to work, generate wealth and climb out of the poverty/subsistence hole in which “caring greens” apparently wish to keep them trapped.”) (junkscience.com)
3. Mosquito resistance is not an issue. “Resistance” is not an issue since this mostly takes the form of avoidance and keeping mosquitoes away from human prey is the intended object anyway” (junkscience.com)
4. DDT is safe.“There never was any scientific evidence that DDT posed a risk to humans or wildlife.” (Fox News)
I’ll leave out all the emotional nastiness of Photoshopping photos of Rachel Carson into wearing a pro-DDT t-shirt (I’m not kidding), and focus on the stuff that as an entomologist, I’m uniquely qualified to comment on. I know about bugs. I know about pesticides. I’ve taught parasitology for over 5 years. Let’s begin with the first two claims. [NOTE: this is a multipart series. Don't miss the other posts!]
Claim 1: Banning DDT in the past caused the deaths of millions of people from malaria. I’m going to break this into two pieces:
Claim 1a: Lots of people die (and have died) of malaria.
This is absolutely correct, and a tragedy. Good on them for being interested in what’s happening. However, the malaria clock on their page is blatantly bogus, and they even admit it!! In tiny tiny type at the bottom of that page:
“Note that some of these cases would have occurred irrespective of DDT use. Note also that, while enormously influential, the US ban did not immediately terminate global DDT use and that developing world malaria mortality increased over time rather than instantly leaping to the estimated value of 2,700,000 deaths per year. However, certain in the knowledge that even one human sacrificed on the altar of green misanthropy is infinitely too many, I let stand the linear extrapolation of numbers from an instant start on the 1st of the month following this murderous ban. — Ed.”
Claim 1b: DDT is/was banned worldwide:
Exotoxnet (Extension Toxicology Network) is maintained by 5 major land grant universities. Their DDT Entry:
“REGULATORY STATUS: DDT is no longer registered for use in the United States, although it is still used in other (primarily tropical) countries. It is in EPA Toxicity Class II, moderately toxic. DDT was banned from use in the United States in 1972, and remains banned barring public health emergency (e.g., outbreak of malaria).”
So, not only is DDT still allowed to be used against malaria elsewhere, if there was a problem in the USA, it could still be used. In fact, most pesticides have a “special use” clause, which allows them to be used even if they are banned.
DDT was named as one of 12 persistent organic pollutants to be banned worldwide in a 2001 Stockholm convention, but parties to the Convention can use DDT for “disease vector control” under guidelines for use set by the WHO (UNEP 2001). There was a great deal of rejoicing by Pro-DDT folks about the recent WHO announcement that they planned to re-implement DDT spraying.
Except…this comment in Lancet (Dec. 2006) from the Former Head of the WHO Global Malaria Programme says it all:
“A recent press statement from WHO about dichlorodiphenyltrichloroethane (DDT) and indoor residual spraying for malaria control caused a considerable stir, despite the fact that, in terms of policy, it merely re-iterated WHO’s endorsement of DDT as a useful insecticide for malaria control.” (Emphasis mine)
It wasn’t a change in policy–it was just a press conference. Ergo: Claim 1b is false.
Claim 1= (1a + 1b): Banning DDT in the past led to deaths of millions of people from malaria.
I’ve already shown that DDT was, and is, still being sprayed long after the 1970’s US ban. Using DDT did work to eradicate malaria in several countries—the incidence of malaria in parts of Central America and Taiwan decreased dramatically, and was completely eliminated in the US.
So, what made DDT fail as a control in Africa, since we still have malaria there? Was it the reduction of sprays in the 1970’s? If DDT spraying had continued, would malaria have been eradicated?
There were many reasons that past DDT spraying programs failed.
There isn’t only ONE kind of malarial parasite (Plasmodium).
There isn’t only ONE species of malaria vector (insect that transmits the disease).
And certainly, there is not just ONE kind of ecosystem in which birds, mammals (including people) and malaria interact.
Each system is different, and that is part of why DDT sprays worked in some places, and not others.
If you would like to read an excellent discussion of some of the immunological differences between the 3 major species of malarial parasites, I refer you to “Yellow Fever, Black Goddess” by Christopher Wills. One of the best layperson’s explanations of the amazingly complex human immune systems around, and he covers differences between the malarias thoroughly. (Learning the malarial life cycle is not for the timid; it’s not surprising it took decades to fully understand it.)
The mosquito vectors differ quite a bit, not just in their individual species, but also in behavior. You have to know a lot about a pest to know where to spray it, when it will be there, and what pesticides it’s resistant to (We’ll come back to the behavior and resistance puzzle later–it’s both interesting and complex enough for it’s own post.)
Malaria in tropical Africa is one of the most difficult to control. Two of the world’s most efficient vectors of malaria are present: An. funestus, a swamp mosquito, and An. gambiae, which breed in temporary pools wherever they occur (this includes footprints, irrigation furrows, potholes, etc.). This area of Africa has never had good malaria control—now or in the past. Why?
“Africa south of the Sahara, except for South Africa and some of the islands, was not incorporated into the global malaria eradication campaign of 1955–1969. Therefore, few of the countries developed the infrastructure to undertake IRS on a national scale.” (IRS= Indoor residual spraying; WHO 2005)
Clearly, cutbacks on DDT sprays weren’t a factor in the failure of malaria control in this large area of the continent. (And potential future sprays aren’t going to work well either.)
What other things may have gone wrong in the past?
“Context-specific factors giving rise to high malaria burdens in complex emergencies include breakdown of health services, concentration of non-immune refugees in malaria risk areas, malnourishment, siting of refugee camps on marginal land prone to flooding or vector breeding, and problems in gaining access or supplying medicine to the displaced population.”
The sad truth is, this is the story of much of Africa. Conflict, movement of refugees, and life on the margins. This is not the optimum situation for mosquito control.It isn’t terribly suprising, given the political turmoil in this area, that a major public health initiative failed. Houses with well-sealed windows and internal plumbing offer better protection against vectors than a UN-issued tent and a water bucket. Malaria is a disease the poor and displaced are especially vulnerable to.
I’ll save discussion of the failures of DDT because of insect resistance for the later discussion, but that certainly factored into the malaria control program failures.
In conclusion, other factors were at work than just the reduced spraying of DDT in the 70s and 80s. There are probably few places where it would have worked; the absolutist statements of “genocide” caused by the DDT ban are clearly way over the top.
Claim 3: DDT spraying now will save millions of people in the 3rd world from malaria.
So, let’s say DDT is approved and easy to get for malaria control. Problem solved? Not really.
In order to have a successful spray program, you need an infrastructure. Quoting again from Lancet (Dec. 2006), the Former Head of the WHO Global Malaria Programme:
“Indoor residual spraying is an effective intervention, provided a programme infrastructure can be set up and maintained to include trained sprayers, supervisors, managers, stocks, equipment, and vehicles, that roads allow access to every village at the right time at least once a year, and that insecticides are not diverted to agriculture.
The need to prevent diversion has been highlighted for DDT, but for malaria control it is equally important for other insecticides. Furthermore, especially in areas with intense and perennial transmission, it is essential to maintain the population’s long-term acceptance of spraying once or several times a year. In view of the difficulties encountered in maintaining indoor residual spraying, WHO has invested substantially in exploring other methods, especially insecticide-treated bednets.”
The problem of training and infrastructure is so huge, the FIRST conclusion and recommendation from the WHO working group was:
“IRS should only be adopted if the necessary infrastructure exists or can be created to achieve and sustain high coverage and where local vectors are susceptible to the insecticides used.”(IRS= indoor residual spraying; WHO 2005; p. 52)
Spraying isn’t just as simple as popping a cork and filling the sprayer. The applicators need to formulate the pesticide correctly, apply it with the correct method, apply it at the correct time, and in the correct place. That all takes training, and the issue of diversion of pesticides to agriculture is not a trivial one. (Especially if you are a subsistence farmer.)
It’s thought that much resistance to DDT developed initially from extensive use of pesticides in agriculture, in addition to malaria control programs. This rapidly created selection pressure for mosquitoes that not only had certain proteins (kbr) that could detoxify DDT, but that had different behaviors. Mosquitoes that didn’t rest inside houses became more important malaria vectors, for example.
Monitoring and managing insecticide resistance to all pesticides used in mosquito control is a major part of the WHO recommendations, and should be a part of all control programs. That takes even more training, organization, and resources.
Public acceptance of spraying is a major issue that I have yet to see addressed by the Pro-DDT camp. I can only imagine the outcry if a group of strangers in face masks arrived in my town and said they were going to spray a white power (the residual after a spray is quite obvious) in everyone’s house. No exceptions.
I predict it would not be a successful program (and not just because of the Michigan Militia.)
Two more points: DDT doesn’t absorb well onto western-style houses that have been painted with synthetic paints, so won’t provide much residual protection for those homes. (It does fine on traditional housing materials of mud and wood.)
Lastly, in “DDT for malaria control: the issue of trade (2007)” it was pointed out that countries choosing to use DDT may face sanctions on agricultural products from the EU. We don’t want to hurt the growing economies of Africa by clinging to an old solution.
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Conclusion
I’ll stop here, since this is quite a lengthy post, and address insect resistance and DDT safety another day.
There is a lot of name calling and rhetoric being thrown around, but the real story is considerably more complex. DDT is not the major factor in the story of malaria—it is one piece of an extremely complicated disease puzzle.
I’m not denying there is data that DDT can make a difference; I’ll use one case study in Eritrea as an example of a success story (Nyarango 2006). They found that DDT, used as PART of an integrated strategy using bednets and other pesticides, effectively reduced malaria transmission by 80%. This is a country, however, that has a “well entrenched” health system in place, and has all the pieces to make the system work (and has been using DDT for the last 10 years, I’ll point out). Their conclusions from the Eritrea study?
“In Eritrea, the use of ITNs contributed most to the reduction in malaria morbidity and mortality….Arguably the most cost effective tool in malaria prevention is the use of ITNs. (ITN=insecticide treated net)
It’s cheap, it works…and it’s been the main focus of the WHO for the last decade. I’m not seeing a problem here. What else worked?
In 2004, more than 80% of the breeding sites in Southern Red Sea, Northern Red Sea and Anseba were covered through active community participation . The remainder was subjected to temephos, a larvicidal chemical…The role of the community was central to the success.”
So, by physically changing the breeding environment for mosquitoes, they were able reduce adults emerging. And no DDT was involved, plus local people were able to have control over the program. An additional global review (Keiser 2005) found that environmental interventions could reduce malaria risk by up to 80%; simple changes like clearing vegetation around houses or putting screens on windows could be effective.
What about DDT in Eritrea?
“The final question to be explored was the role of each of the interventional measures in reducing morbidity or mortality. Within the limitations of the current study design it is evident that combining ITN use with IRS or other vector control measures did not confer added value to the outcome in malaria mortality or morbidity.” (ITN=insecticide treated net; IRS=indoor residual spraying)
DDT helps, but it isn’t a magic bullet. I wish that it was the panacea that the pro-DDT folks made it out to be—but it isn’t.
———-
Publications cited not available online:
Nyarango, PM, et al. A steep decline of malaria morbidity and mortality trends in Eritrea between 2000 and 2004: the effect of combination of control methods. MALARIA J 5: – APR 24 2006
DDT for malaria control: the issue of trade. Lancet 2007 Jan 27; 369(9558): 248
Keiser, J, et al. Reducing the burden of malaria in different eco-epidemiological settings with environmental management: a systematic review
LANCET INFECT DIS 5 (11): 695-708 NOV 2005
EDITED 6/17 to add link to the second in the series, DDT and insecticide resistance
EDITED 8/10/07 to add link to collection of all posts on this topic by myself and others.
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