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Does DDT Have A Place in Today's Malaria Vector Control?

 

By: Manuel F. LLuberas MS, IDHA

When Othmar Zeidler first synthesized dichloro-diphenyl-trichloroethane in the nineteenth century with apparently no particular purpose in mind, he could not have foreseen the controversy that would follow his invention two Centuries later. DDT was manufactured in 1874 as part of what today could probably be considered a science fair project. In 1939, Dr. Paul Müller independently produced DDT and patented it a year later in conjunction with the Giegy Corporation. By 1948, DDT had proven itself so effective against so many different insect vectors of disease that Dr. Müller was awarded the prestigious Nobel Prize for his work on this insecticide. By the end of the 1990s, the early pages of history exulted DDT as the panacea against the scourge of malaria and many other vector-borne diseases and insect pests while later chapters labeled it as the scourge that would irreversibly damage the environment and be single-handedly responsible for the demise of many animal species and possibly the entire human race.

The Eighth World Health Assembly introduced DDT as a tool in the Global Malaria Eradication Campaign that started in May of 1955. By 1967, malaria had been eradicated from all developed countries where the disease was endemic and large portions of Latin America and Asia were freed from the risk of infection. The impact DDT had over malaria was such that in 1970, the Committee on Research on the Life Sciences of the Committee on Science and Public Policy of the National Academy of Sciences was quoted as saying "To only a few chemicals does man owe as great a debt as to DDT. In little more than two decades, DDT has prevented 500 million human deaths, due to malaria, that otherwise would have been inevitable." Thirty years later, the statement remains valid, though the current figure could easily be well into four times what was quoted.

The success of the integrated vector control programs against malaria vectors in the Zambian Copper Belt in the 1930s and 1940s and those of the Global Malaria Eradication Campaign of the 1960s that eradicated malaria from the United States and many other countries provide us conclusive evidence that strategically-sound and well-coordinated and designed vector management initiatives can bring about enormous tangible benefits and improved health and socioeconomic development. Unfortunately, many of these programs have fallen victims of their own successes and were discontinued or cancelled when they were viewed as unnecessary or no longer needed.

Sadly, at the end of the 1999, it is estimated that there were somewhere between 300 to 500 million global cases of malaria, with somewhere between 1.5 to 2.5 million deaths, mostly on children under five years old. Moreover, though the effectiveness of integrated vector management has been demonstrated to be an affective and invaluable tool against vector-borne diseases like malaria, Chagas disease and many others, they are often viewed as exercises in futility or as useless and irresponsible. Furthermore, though DDT remains a viable and valuable tool against many vectors of public health importance, having DDT in the arsenal of many integrated vector management programs adds another dimension, as many consider this insecticide detrimental to the environment and harmful to humans. These opinions, however, are often expressed by many who do not know, or chose to ignore the history of the hostilities between mosquitoes and man, people have not witnessed the devastating effects of malaria on a child or those who have lost themselves in the opinions and expressions of others that are based on speculation and incomplete science. Many experiments on caged birds, for instance, have demonstrated that DDT and its metabolites (DDD and DDE) did not cause serious eggshell thinning, even when these birds were fed DDT at levels many hundreds of times greater than the wild birds would ever ac-cumulate. Other studies found egg shells about 7% thicker after two years on a DDT diet. Moreover, a study published in the Journal of the American Medical Association showed that men who were carefully examined after voluntarily ingesting 35 mg of DDT daily for nearly two years "developed no adverse effects." Furthermore, 35 workers exposed during 9-19 years to DDT at 600 times the average US exposure levels showed no evidence of cancer, as reported in the Archives of Environmental Health.

These and many other studies demonstrate that many individuals arguing against the use of DDT in public health vector control have completely ignored one irrefutable fact: DDT has saved and continues to save lives! The effects of properly planned and executed integrated vector management programs can be seen today in portions of southern Africa. Zambia, for instance, has made significant strides against malaria in the last few years. After years of operating a national malaria control program which relied almost exclusively on the use of impregnated mosquito nets and therapeutic drugs against the disease, the Zambian National Malaria Control Program and the Central Board of Health reported more than 2 million malaria cases and an estimated death toll of over 50,000 lives by the end of 2002. While public health authorities were feverishly fighting malaria following the "conventional approach" and trying to explain to their citizens why malaria continued to afflict them, a few private corporations in the Copper Belt area were quietly re-structuring their RBM-based programs to include indoor residual spraying, or IRS. These programs began operating in an integrated fashion, erecting physical and chemical barriers against the vectors and the plasmodia while simultaneously seeking the support of country leaders and enlisting the assistance of the general population and the media.

By the end of the rainy season of 2003-2004, the malaria vector control programs in the Copper Belt area had not just reduced the incidence the disease, they had pushed malaria several notches down from the top of the list of communicable diseases and eliminated malaria-related mortality from many areas. Moreover, the programs have been instrumental in reducing the rate of absenteeism and increasing productivity in several copper mines. The success of malaria control program in the Copper Belt region, and especially its vector control component inspired the national malaria control program to adopt the Copper Belt model and implement it at national level. Together, Zambia's public and private sector, including international, private corporations like H.D. Hudson Manufacturing Company, have joined hands to fight malaria with very positive and tangible results. The results of this partnership are so encouraging (publications are in progress) that several countries in southern Africa are looking at establishing it as the template for collaboration. It should be noted that the success of this model is due in great part to the dedication of Zambia's vector control teams and their managers and to the manner in which they met the challenges of the revitalized national malaria control program. In addition to the obvious challenges inherent to this type of collaboration, the introduction of residual insecticide applications brought with them challenges and opportunities unfamiliar to many. This was especially evident when DDT was added to the vector control arsenal. In light of the restrictions and limitations imposed by the Stockholm Convention on Persistent Organic Pollutants (POPs), specific information pertaining to the procurement, handling, transport, use and disposal of DDT and DDT-contaminated rinse water were incorporated in the indoor residual spray team training conducted prior to the beginning of each malaria control season. The goal of this training was to ensure that all team members and supervisors understood the Convention's implications and were able to answer basic inquiries from the general population benefiting from their activities. In addition, steps and procedures were instituted to enhance personal and environmental safety precautions, minimize the chances of inadvertent or accidental release of DDT in unwanted areas and reduce the risk of unauthorized use of the insecticide.

In summary, the integrated malaria vector control programs implemented in Zambia and other parts of southern Africa have provided tangible proof that the use of DDT as part of an indoor residual spray campaign is effective in bringing the disease to a manageable level. These programs provide a glimmer of hope to the countries where they have been implemented and to the surrounding countries also afflicted by this devastating disease that have not been able to implement their own programs. The long history of the hostilities between man and vector provide us with many powerful examples of the successes of properly managed and oriented vector control programs. Vector management professionals need to be proactive in promoting their activities and dispelling the myths and common misconceptions associated with the use of insecticides for vector control. Only then we will be able to reduce the impact of these dreadful diseases.

References:
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WHO, Geneva, 2004 (WHO/CDS/CPE/PVC/2004.10): Global Strategic Framework for Integrated Vector Management WHO/CDS
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