Sometimes I will post things I have written for my MPH classes if I think the subject is interesting or timely. This is a forum post I wrote for my Environmental Health class about whether we should bring back DDT, an insecticide used to combat malaria in the United States that was later banned because of environmental hazards.

I have been inclined to believe that it is not a good idea to reintroduce DDT because of its hazards. The fact that it has been banned in the United States indicates that there must have been significant adverse effects. However, I believe that forming a truly informed stance requires looking at both sides of an issue and seeking out information that may undermine  my current stance on a subject. So I went looking for articles on the benefits of DDT and why it should be used against malaria in places like Africa. A couple of examples of articles supporting DDT that I found were “Thirtieth Anniversary Of Misguided Ban On DDT Without This Pesticide, Millions Die Of Malaria, Says Health Group; Senate To Extend Ban” by the American Council on Science and Health (2002) and “What the World Needs Now is DDT” (Rosenberg, 2004). The main arguments I found supporting the use of DDT were as follows:

  • DDT is very effective at eliminating malaria and is responsible for the elimination of malaria transmission in the United States and other countries.
  • There is no evidence that DDT poses harm to humans, while malaria is a serious health threat known to take many lives.
  • DDT is the most cost effective way to eliminate malaria in developing countries.

So my next task was to look at each of these arguments and find out what evidence there was for and against them. So starting with my first bullet point:

DDT is very effective at eliminating malaria and is responsible for the elimination of malaria transmission in the United States and other countries. DDT is very effective at killing mosquitos and it was a big part of the malaria elimination campaign in the United States. I think the issue is whether DDT is the most crucial component of malaria elimination. Much of malaria elimination campaign in the United States was focused on spraying DDT, but it also included drainage and removal of mosquito breeding sites (Centers for Disease Control, 2012). So while DDT was widely used during the malaria elimination campaign altering the environment to discourage mosquito breeding was also a part of fighting malaria. I know this seems like heresy, but I have to wonder if drainage, better indoor plumbing and sewage systems and the removal of mosquito breeding sites may have actually provided a longer term solution to malaria transmission. After all, DDT hasn’t been used in the United States for decades and we still have mosquitos, but malaria isn’t a serious public health threat here. So just because we used DDT to fight malaria transmission, doesn’t necessarily mean that it was the most effective tool against malaria or that it will save Africa from malaria without other efforts like drainage and sewage control. Moving on to the next point…

There is no evidence that DDT poses harm to humans, while malaria is a serious health threat known to take many lives. People usually take this to mean that something is proven to be safe, but that’s not what “no evidence of harm” means. “No evidence of harm” was the same strategy used to convince the public that tobacco didn’t increase the risk of cancer and that the use of lead in gasoline, plumbing and paint was benign. “No evidence of harm” can simply mean that no studies have been done on the effects that a substance has on humans. In reading through the report on DDD, DDE and DDT from the Agency for Toxic Substances and Disease Registry (ASTDR), I found that for many side effects on humans and animals there were simply no known studies available.

For example, in relation to the effects of DDT and its related compounds DDD and DDE on kidneys, the report says “No studies were located regarding renal effects in humans after oral exposure to DDT, DDE, or DDD.” This doesn’t mean that DDT has been proven to be safe for human kidneys, it just means that there aren’t any studies that have looked at that aspect yet. If DDT is harmful to the human renal system, not having any studies won’t actually change its toxicity; all it means is that studies haven’t been conducted on it. (However, studies on rats have shown some adverse effects to rodent kidneys.)  The report does cite some studies which have shown a higher incidence in lung cancer to some workers who are exposed to DDT and others showing elevated levels of liver enzymes with high exposure. DDT is known to cause adverse neurological effects in both humans and animals, though as the report states, “Few studies have explicitly evaluated neurotoxicity in humans following chronic exposure.” Again, it doesn’t mean that DDT has no neurological effects on humans at chronic exposure levels, simply that there is very little research on the subject. According to the report from the ATSDR, DDT is known to cause harm to the endocrine and reproductive systems of animals and there is research pointing to immunological damage as well.

But for the sake of argument, let’s assume that DDT is only harmful to animals and will eliminate malaria transmission without extensive work on sewage and drainage systems or other measures. Does this make it a good strategy for malaria control in humans? I think to answer this question we need to consider how far we really can remove ourselves from the health of the environment. If the water, air, plants and animals around us are damaged from toxic chemicals, will we really be spared any ill effects? I think this question is especially relevant when we are talking about about Sub-Sahara Africa where many people still rely on subsistence farming. Also, Sub-Sahara Africa is home to many rare and endangered plants and animals. If DDT is used in these countries and it does eliminate malaria transmission, will it cause more trouble by damaging the land and animals? If people rely on the health of their cattle, pigs and chickens to sustain them and these animals become sick and can’t reproduce, we might be looking at a situation where people could suffer further from poverty, malnutrition and starvation. Because DDT persists for long periods of time in the environment, if it is used in areas with rare and endangered species it could cause irreparable damage to the ecosystems of these places. And heading into the homestretch on what has become a near treatise at this point…

DDT is the most cost effective way to eliminate malaria in developing countries. The issue of DDT and malaria elimination gets at the heart of a lot of issues about what it means to actually help people in developing countries. If you think about it, we are presuming a lot when we in America discuss how to solve a problem in another country with a different culture thousands of miles away. Mosquito nets are an example of another strategy that is popular with Westerners as a way for people in Africa to fight malaria, but in some areas malaria is so common and most cases go away on their own that most people don’t even consider using a mosquito net. Sonia Shah (2010), author of The Fever: How Malaria Has Ruled Humankind for 500,000 Years, compares malaria in these regions to the flu in North America- it can kill, but many recover without ill effects. She compares mosquito nets in these areas to face masks in cold and flu season. If you handed out free face masks to everyone in your neighborhood during cold and flu season to wear every time they go out in public, how many people would wear them, even if it would stop transmission of the disease? And even if everyone used a mosquito net, the nets wear out and need to be replaced, so they’re not a long term solution. I think the issue of DDT is much the same way. We used DDT as did many other countries, and so we assume that developing nations should too. But it may not be the best answer for them.

I think Shah really sums it up best when she writes, “Perhaps what we need is a whole new approach. Instead of masterminding solutions for distant problems and then handing them down from on high — as we do not just in our anti-malaria efforts but in a variety of aid programs aimed at extreme poverty — we should empower the poor to come up with their own solutions, and then help figure out how to implement them. Such a process might not lead to grand, magic-bullet solutions. More likely, we’d get micro-solutions, variable from locale to locale, from village to village. But we’d be supporting self-reliance and building goodwill along the way. And we’d surely avoid the wastefulness — and really, the affront — of befuddling communities with “gifts” that many neither want nor use.” While she is referring specifically to mosquito nets and malaria, I think the same applies to DDT.

Also, mosquitos may be carriers of disease, but they are also part of the eco-system as are any naturally occurring pathogen or pest, whether it be viruses, bacteria, fleas or rats. The idea of DDT is that if we can kill the mosquitos we can stop the spread of malaria. But here’s the thing, mosquitos have been on the Earth for tens of millions of years. In order to do that they have had to be pretty adaptable and even with their primitive biology they are already starting to outsmart us. In some areas, cases of DDT resistance has been reported in mosquitos (Dasgupta, 2012).

DDT is not a magic bullet. If DDT is employed for malaria control, it should be used with extreme caution and to a minimum to prevent resistance and side effects, much like antibiotic stewardship. Dasgupta’s (2012) conclusion from the World Bank’s blog sums it up better than I can: “Continued use or reintroduction of DDT in malaria control should call for a careful country-by-country assessment of costs and benefits based on a country’s circumstances. Other vector control measures, such as larvicidal and environmental management may also be -necessary – when appropriate – based on scientific evidence.”

References

Agency for Toxic Substances and Disease Registry (n.d). DDT, DDE and DDD: Health effects. Retrieved from http://www.atsdr.cdc.gov/toxprofiles/tp35-c3.pdf

American Council on Science and Health Staff(2002, June 12).  “Thirtieth Anniversary Of Misguided Ban On DDT Without This Pesticide, Millions Die Of Malaria, Says Health Group; Senate To Extend Ban”. Retrieved from http://acsh.org/news/2002/06/10/thirtieth-anniversary-of-misguided-ban-on-ddt-without-this-pesticide-millions-die-of-malaria-says-health-group-senate-to-extend-ban

Centers for Disease Control and Prevention (2012). Elimination of Malaria in the United States (1947 — 1951). Retrieved from https://www.cdc.gov/malaria/about/history/elimination_us.html

Dasgupta, Susmita (2012, October 23). “Health costs and benefits of DDT use in malaria control and prevention.” Retrieved from http://blogs.worldbank.org/developmenttalk/health-costs-and-benefits-of-ddt-use-in-malaria-control-and-prevention

Rosenberg, Tina (2004, April 11). What the world needs now is DDT. New York Times Magazine. Retrieved from http://www.nytimes.com/2004/04/11/magazine/what-the-world-needs-now-is-ddt.html?_r=0

Shah, Sonia (2010, May 2). In Africa, anti-malaria mosquito nets go unused by recipients. Los Angeles Times. Retrieved from http://articles.latimes.com/2010/may/02/opinion/la-oe-shah-20100502

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