DDT Use and Malaria: Review and Position Statement

Author:  Clint Slaughter, M.D., Walden University MPH Student, 4/7/2009

Significance of Malaria

Introduction
Malaria is a protozoan that is transmitted to humans through a carrier Anopheles mosquito and is the most important parasitic disease to affect humans (Braunwald, 1998, pg. 1180).  According to the World Health Organization’s (WHO) World Malaria Report 2008, there were approximately 247 million cases of malaria in 2006, 86% of them occurring in Africa, and leading to an estimated 881,000 deaths (2008).  Malaria rates peaked around 5 million cases per year in the 1930’s (Gates, 2009), and although significant progress has been made in the prevention and treatment of the disease, it is and will continue to be a major battleground for public health efforts.

Pathophysiology
There are four types of malaria that infect humans, Plasmodium vivax, Plasmodium ovale, Plasmodium malariae, and Plasmodium falciparum, with nearly all of the severe cases leading to death being caused by the falciparum subtype (Braunwald, pg.1180).   Frighteningly, the WHO estimates that 91% of the malaria cases in 2006 were due to this deadly strain of the disease (World malaria report, 2008).  The lifecycle of the parasite is important to understand so that effective interventions can be made to decrease transmission.  Humans are an essential part of this cycle, with malarial gametocytes being ingested by a mosquito during a blood meal from an infected human, which then form zygotes that then mature into infective sporozoites that migrate to the insect’s salivary glands.  These sporozoites are then injected into another human during another blood meal, starting the next phase of the lifecycle.  In human liver cells, the sporozoites develop into schizonts, which produce and release merozoites into the bloodstream.  Interestingly, in the ovale and vivax malarial subtypes, some of these organisms become dormant and stay in the liver cells, only to be reactivated sometimes years later with acute infection.  Once in the blood, the merozoites invade red blood cells where they further mature into hemoglobin-consuming trophozoites that then make more merozoites that are released when the red blood cell is spent and the cycle continues (Braunwald, pg 1180-81).
Active malaria infection causes a variety of symptoms including cyclic fevers, the lysis, or breaking of red blood cells that carry oxygen to the body, splenic enlargement and rupture, cerebral malaria with encephalopathy and coma, hypoglycemia, acidosis, kidney failure, and sometimes death (Braunwald, pg 1182-83).  Malaria has been a human health risk for so long, that mutations have arisen to protect certain populations from the disease, the most well-known being sickle-cell trait, where carriers have abnormal hemoglobin leading to early rupture of red blood cells that stops the intravascular reproductive cycle.  Glucose-6-phosphatase (G6PD) deficiency is an enzyme deficiency that acts similarly to sickle-cell trait (Braunwald, pg 663).  Also, certain populations in endemic malarial areas lack the Duffy blood-group antigen, which is required for P. vivax to infect cells (Braunwald, pg 1180).  Although the mutations can be beneficial in preventing severe malaria infections, they can also confer other health problems, since those homozygous for hemoglobin S, the sickle-cell trait, are very sensitive to low oxygenation or stress, lysing red blood cells even without a malarial infection, while those heterozygous for the trait with only one gene are protected from malaria with only minimal other effects (Braunwald, pg 648-50).

Intervention and control
The approach to intervention and control of malaria has already run the gamut, with governments, non-governmental organizations (NGOs), healthcare professionals and the like, utilizing the clinical intervention model, the public health intervention model, and the environmental stewardship model in attempting to decrease malaria transmission, morbidity and mortality (Moeller, 2005).  The clinical intervention model treats those who have already become ill, using chloroquine, mefloquine, or quinine, depending on the subtype and severity of the disease (Harrison’s, pg 1187).  Malaria is indeed treatable, but causes worse disease and has increased mortality However, because of the pervasiveness and severity of the disease, the public health intervention model must be used as well to educate those at risk with preventative practices.  Environmental stewardship is also paramount in fighting the disease to control the vectors to human disease.  There are many approaches to this model in regards to malaria, such as eliminating mosquito breeding areas (Sibbald, 2002) and the use of chemical agents such as DDT or peremptoriness to kill mosquito populations and mosquito larvae.  Some of these environmental approaches, such as the use of DDT, have demonstrated significant human health and environmental side effects that may outweigh the risks of the disease.  Bill Gates, who’s foundation has become a major player in the global fight against malaria, discussed some of these challenges in his TED talk this February, citing that treated nets plus indoor DDT spraying can cut deaths by over 50% (Gates, 2009).  Gates also addresses some of the challenges that we face in that not only can the malaria parasite itself develop resistance to drugs, but the vector mosquitoes also become resistant to insecticide.

Impact of DDT

Use of DDT
DDT, or 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane, was used extensively as an agricultural and domestic insecticide from the 1930’s to the 1970’s when it was banned in many countries, including the U.S..  It is a type of organochlorine pesticide that has a wide range of effectiveness against mosquitoes as well as many common agricultural insects such as potato beetles, the coddling moth, corn earworm, the cotton bollworm, and tobacco budworms (DDT: An Introduction, N.D.).  Because of its broad spectrum effectiveness and low cost, DDT saw wide use around the world beginning after WWII.  In the decades following, however, the agricultural application of the chemical caused widespread contamination of water, air, and soil, and was found to persist for decades in the environment (Toxicological Profile, 2002).

Toxicity
Similarly to other pesticides, DDT causes significant toxicity with large acute exposures or overdoses, causing neurologic impairment, headache, vomiting, tremors, and other effects (Third National Report, 2005), and after a few decades if use, it was blamed for many environmental phenomena as well.  In 1962, Rachel Carson, an environmental activist, wrote Silent Spring, a book documenting declines in bird populations, the presence of the chemical in fish, livestock, pets, and humans, and an association with cancer (Raloff, 2000).  After the publication of the book, public awareness and concern about the dangers of the widespread use of DDT became such that by the mid-1970’s, many countries such as the U.S. and much of Europe, had banned the use of the chemical.  The heavy use of DDT over just 40 years led to quantifiable changes in wildlife, as well as pressured insects such as mosquitoes, to begin demonstrating resistance to the chemical (Matambo, et al. 2007).  Encouragingly, since the ban, the bird populations affected have rebounded (Glausiusz, 2007).

DDT Controversy
DDT has remained in use in some areas and over the last few years has been in somewhat controversial use once again against mosquitoes in the fight against malaria.  Part of the reasoning behind this is the difference in usage, small-area spraying verses spraying entire agricultural areas, as well as an alarming rise in malaria cases in some areas since the ban, attributable to greater difficulty controlling mosquito populations without DDT (DDT: An Introduction, N.D.).  Over the decades since DDT was banned, more detailed information has been uncovered about its true effects on environmental and human health.  It seems that Carson was correct and even may have underestimated DDT’s effect on bird populations and hormonal influences on fish and amphibians (Raloff, 2000).  More research on the carcinogenic effects of the chemical show that the age of those exposed plays a role in risk for cancer, demonstrating an increased risk with exposures at younger ages (Cohn, Wolff, Cirillo, & Sholtz, 2007).  Continuing studies of the effects of DDT have also shown that rather than causing a large increase in cancer risk, it has similar estrogen-mimicking effects to many of our present-day chemical exposures such as Bisphenol-A and phthalates, as well as many modern, approved pesticides and fertilizers, increasing the risk of certain types of cancer with long-term and cumulative exposures (Third National Report, 2005).

Position Statement
Malaria is one of the most significant preventable and treatable diseases to continue to scourge humankind, so much so that it is one of the only environmental pressures through which we can actually see human evolution at work to protect ourselves against it in the form of sickle cell trait and G6PD deficiencies.  Malaria needs to be fought on many fronts:  education and prevention, eradicating the vector, the Anopheles mosquito, as well as medically treating the parasite itself once it has infected a human.  The more people infected, the more reservoir sources mosquitoes have to continue the lifecycle of malaria, the more mosquitoes, the more chance to infect more humans, and the cycle continues.
DDT is, thus far, the most effective chemical agent we have against mosquitoes and has been proven to decrease transmission of malaria when sprayed in homes (Gunasekaran, Sahu, Jambulingam, & Das, 2005), especially in conjunction with other prevention measures.  Despite this, DDT has been shown to cause significant environmental damage when used in large quantities for agricultural use, effecting avian and fish populations, pressuring mosquitoes to become resistant, as well as causing human health problems with moderate or high level exposures.
Although the decision to ban the use of DDT as an agricultural pesticide in the 1970’s was correct and should be upheld, the reasonable use of DDT to fight malaria continues to be a question of risk verses benefit.   At this juncture, the malaria epidemic in certain parts of the world, especially in Africa, does justify the use of DDT for this purpose specifically.    However, vigilance must be maintained and continued research is imperative to find more sustainable and less toxic methods to fight the disease, realizing that overuse of any chemical or method, be they pesticide or drug, will pressure these organisms to adapt and become resistant to our efforts.  DDT should be nothing more than a bridge to keep the malaria epidemic at bay as we look at improvements in mosquito control methods, through both environmental and chemical means, improvements in treatment of the disease itself, as well as continued efforts towards a vaccine.

References:
Braunwald E, et. al., (ed.) (1998). Harrison’s Principles of Internal Medicine, 14th ed. New York, New York: McGraw Hill.

Centers for Disease Control (2005).  Third National Report on Human Exposure to Environmental Chemicals.  Retrieved on April 2, 2009 from: http://www.cdc.gov/exposurereport/pdf/results_08.pdf

Cohn, B., Wolff, M., Cirillo, P., & Sholtz, R. (2007). DDT and breast cancer in young women: New data on the significance of age at exposure. Environmental Health Perspectives, 115(10), 1406–1414. Retrieved on April 2, 2009 from Walden Library Academic Search Premier database.

Duke University (n.d.).  DDT:  An Introduction. Retrieved on April 2, 2009 from: http://www.chem.duke.edu/~jds/cruise_chem/pest/pest1.html

Gates, W. (2009).  TED Talks Bill Gates:  How I’m trying to change the world now (Video).  Retrieved on April 2, 2009 from: http://www.ted.com/index.php/talks/bill_gates_unplugged.html

Glausiusz, J. (2007, November). Can a maligned pesticide save lives?. Discover, 28(11), 34-36. Retrieved April 2, 2009, from Academic Search Premier database.

Gunasekaran, K., Sahu, S., Jambulingam, P., & Das, P. (2005, February). DDT indoor residual spray, still an effective tool to control Anopheles fluviatilis-transmitted Plasmodium falciparum malaria in India. Tropical Medicine & International Health, 10(2), 160-168. Retrieved April 2, 2009

Lewis, K. (2008, November 4). DDT stalemate stymies malaria control initiative. CMAJ: Canadian Medical Association Journal, 179(10), 999-1000. Retrieved April 2, 2009, from Academic Search Premier database.

Matambo, T., Abdalla, H., Brooke, B., Koekemoer, L., Mnzava, A., Hunt, R., et al. (2007). Insecticide resistance in the malarial mosquito Anopheles arabiensis and association with the kdr mutation. Medical & Veterinary Entomology, 21(1), 97-102. Retrieved April 2, 2009, from Academic Search Premier database.

Moeller, D. W. (2005). Environmental Health (third ed.). Cambridge, MA: Harvard University Press.

Raloff, J. (2000, July). The Case for DDT. Science News, 158(1), 12. Retrieved April 2, 2009, from Academic Search Premier database.

Salazar-García, F., Gallardo-Díaz, E., Cerón-Mireles, P., & Borja-Aburto, V. (2004). Reproductive Effects of Occupational DDT Exposure among Male Malaria Control Workers, Environmental Health Perspectives, 112 (5), 542-547.

Sibbald, B. (2002). DDT use finally eliminated in North America. CMAJ: Canadian Medical Association Journal, 166(10), 1322. Retrieved April 2, 2009, from Academic Search Premier database.

World Health Organization (2008).  World malaria report 2008.  Retrieved on April 2, 2009 from:  http://www.who.int/malaria/wmr2008/

U.S. Department of Health and Human Services (2002).  Toxicological Profile for DDT, DDE, and DDD.  Retrieved on April 2, 2009 from:  http://www.atsdr.cdc.gov/toxprofiles/tp35.html

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13 Responses to “DDT Use and Malaria: Review and Position Statement”

  1. Our biggest concern in the southeast US is the cold winter and warm spring are leading to the mosquito variety that carries west nile virus. already 2 confirmed cases in the Atlanta Ga area.

  2. The truth will set you free. If you watch this film you will have a tremendous amount of easily verified information that is based on FACTS. There is no excuse for 3 Billion people dying – absolutely none – all because of the words of one woman. Was it written in stone. The climate control scandal is parallel to the DDT mess. Watch is movie and learn. It is your country and your world. How hard is it? Be different, get involved. Find out that DDT is harmless – Rutledge Taylor proved it…

  3. Anni, I know of the film…

    Pretty funny, this concerning DDT… I have been chatting with various folks about the it and my partner said that he used to play in the DDT spray when he was a kid—and he is normal (well… mostly LOL).

    The guy doing my emissions test today said that he and his friends used to ride their bikes in the clouds behind the DDT truck and he said he doesn’t have cancer and is just fine!

    I’ve been learning more so I can be up on it when I do chat. I like the film’s site, so, thought I’d share it:

    http://www.3billionandcounting.com

  4. Thanks for the comments, but unfortunately anecdotal evidence of people playing in DDT is not valid science. Also, if you’ll notice the gist of my article is that while DDT is harmful to wildlife and humans on the scale previously used in agriculture, and well supported since Silent Spring was published, small scale use to combat malaria is reasonable and justifiable. My position is very similar to the movie in that when all considerations are taken into account, the use of a toxic substance can to more good than harm in certain situations. While it is true that agricultural-scale use of DDT caused significant problems with bird reproduction, bioaccumulates in fish and livestock, and increases the risk of cancer, spraying small amounts on mosquito netting or the walls of homes in malaria endemic areas can save thousands of human lives and outweigh the health impacts. Be cautious of reactionary viewpoints based on fear and partial truths. DDT is by no means harmless but can have reasonable uses. Climate change is also very well supported and is certainly not a scandal if you are able to synthesize actual scientific data rather than relying on media hype response to an issue.

  5. After seeing the documentary, 3 BILLION AND COUNTING, at a recent prescreening in L.A., I’m interested in seeing the science which Rachel Carson used to back up her book, Silent Spring. Could you help me with this? Also, I’d like to know what was in the thousands of pages of testimony given to the EPA prior to the banning of DDT? Any help you could be, would be appreciated!

  6. I had no idea that all of this was going on until I was talking to a friend who told me about the 3 Billion and Counting web site and I checked it out. I am following all of this now and want to learn more. I will not be able to be at the premier but appreciate all info. on this subject.

    • Looking at the information on the 3 Billion and Counting website, they seem to be misrepresenting the ban on DDT, which is on agricultural use, rather than vector control use to combat malaria. As far as I can tell, there is no scandal, as DDT is still used to fight malaria throughout the world. However, comprehensive approaches to mosquito control are most effective, which include education, decreasing breeding grounds, bed netting, the use of chemicals like DDT, as well as other complimentary and less toxic alternatives.

      My article above is a well researched presentation of the malaria and DDT controversy, with references for original sources for the information behind it. We’ll have to see how well referenced the film is and if they’re representing all sides of the issue honestly or if they’re creating a scandal out of a misunderstanding of the reality of the DDT saga.

  7. I just wondered .. since you mention that Bill Gates stated “that treated nets plus indoor DDT spraying can cut deaths by over 50% (Gates, 2009”
    WHY would this not be set in place .. NOW .. and let everyone check out the facts .. while lives are being saved .. instead of lost? I went to http://www.3billionandcounting.com and found incredible information about many things, besides DDT. But it is obvious, the argument over DDT is not over. I just hope that while the fight over it continues .. they allow the indoor spraying to begin to save lives.

  8. The Environmental movement in the 60’s as a political force began with DDT being used as a rallying pivotal point. There had to be a compelling argument. Thus the DDT ban fit the bill. It not only provided for the population control maxim. Which is central to this ecological philosophy which revolves around the concept of the “web of life” or inter-connectedness of nature as an ecosystem. The view being that “man” is subservient to nature. This worship of nature as a religion looks upon man as a disturber of the ecological system. So this intruder must be reduced or eliminated in order to save “mother nature”. Thus we have eugenics disguised as population control.

    This DDT ban also provided for another facet of the environmental doctrine. This being the protection of wildlife. It is here that the “wildlands” project comes into play. This being that room or space must be made available for the wildland habitat. Again man and industrialism is seen as a disturber of this balance.

    Thus DDT was the perfect vehicle to achieve the furtherance of this nature religion into the political realm. By vilifying DDT and banning it politically. It provided for humans and industrialism, which are the major obstacle in the way of mother nature, to be eradicated in mass quantities and displaced from disrupting the wildlands.

    There is so much more to this than meets the eye. But for now a good start is this revealing documentary by Dr. Rutledge titled 3 Billion And Counting. I have not seen the film yet but have done lots of digging into this topic. The website http://www.3billionandcounting.com offers a good starting point in the unraveling of the greatest hoax thus far perpetuated against mankind

  9. fishydude Says:

    The DDT ban was part of the Zero Population growth movement. Purely political. Had nothing to do with science. Margaret Sanger would have been proud. After all, she started planned Parenthood for the same reason. The slow the population growth of “undesirable people.”

    • fishydude,
      That sounds like an unfounded conspiracy theory to me. While zero population growth is an important aspiration from a sustainability standpoint, it is certainly unacceptable to imply that we should be actively discriminating against people. Rachel Carson’s “Silent Spring” published in 1962 is what triggered the response to DDT, as it uncovered the significant effects to bird populations and persistence in the environment when used at agricultural levels. Although some groups still want DDT banned entirely, most reasonable public health professionals and environmentalists agree that it is still useful in small amounts to combat malaria, certainly the lesser of two evils.

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