DDT as a Cost Effective Solution for Improving Public Health Through Disease Vector Control
DDT is a synthetic chemical originally used primarily as a pesticide. It was first synthesized in 1874, but its use as a pesticide remained unknown for another sixty-five years, when Dr. Paul Mueller of Switzerland discovered it (West 1952, EPA 1975, Dunlap 1981). By 1945, DDT was used globally in agricultural pest control and this continued until 1959, when it declined due to the combined effects of increased insect resistance, the development of alternative pesticides, growing public concerns, and increasing government restrictions (EPA 1975, Turusov 2002). DDT is currently banned for all purposes other than disease vector control. (Tren 2004, WHO 2004)However, this brings us to the following question: why is DDT still used if there have been concerns about it for the past fifty years?
Simply put, the benefits outweigh the costs, at least currently. DDT is considerably less toxic to humans than its alternatives, while also repelling and eliminating troublesome insects. Another benefit of DDT is the fact that it is far cheaper than alternatives and often needs to be sprayed in areas less frequently. Furthermore, if DDT remains limited to only disease vector control in the ways mandated by the recent Stockholm Convention, there are minimal negative effects on the environment. All of this demonstrates that at the current time, the benefits of the use of DDT for public health controls outweigh the costs.
DDT, or dichlorodiphenyltrichloroethane, is synthetically made by condensing chloral hydrate with chlorbenzene in concentrated sulfuric acid (U.S. Department of Health and Human Services 2002). It is referred to as an organochlorine insecticide, one of four chemical classes of insecticides recommended by the World Health Organization for indoor residual spraying (FAQ on DDT use for disease vector control 2004). In order to prevent insecticide resistance, many unrelated insecticides are used in combination or rotation. Since DDT is the only insecticide from the organochlorine class represented in the World Health Organization’s recommended insecticides for indoor residual spraying, it plays a huge role in malaria vector control and cannot be discarded until inexpensive, effective alternatives can replace it (The use of DDT in malaria vector control).
DDT is tremendously easy and inexpensive to produce for indoor residual spraying. Alternatives to DDT can cost “two to twenty-three times the basis of cost per house per six months of control” (Walker 2000). In addition, “it seems that pyrethroids cost two to three times as much as DDT per house sprayed, given that, in low income countries, the insecticide represents a larger share of a [program’s] cost than spraymen’s wages” (Curtis & Lines 2000). These numbers only include the costs of the chemical and its distribution. When comparing costs, one must also consider how the use of DDT reduces or eliminates the costs that diseases such as malaria and typhus create.
Since most areas affected by malaria and typhus are poor, rural areas that cannot afford alternative insecticides, the fact that DDT is so easy to produce is beneficial to countries affected by diseases that can be eradicated by IRS (indoor residual spraying). Currently, DDT is produced by companies in China and Mexico (U.S. Department of Health and Human Services 2002). Its production could be extended to the poor and rural areas where the risks of contracting malaria or typhus are extreme, thus eliminating or decreasing the costs of DDT shipments while allowing semi-stable and developing countries to become more economically and politically self-sufficient (Even if countries that need IRS are not stable, their access to controlled DDT for emergency public health control will be increased with DDT factories in more locations). The only people who might not benefit from increasing disease-stricken countries’ access to this life-saving chemical are the chemical companies themselves. Chemical companies would benefit if we were banning DDT use, on the other hand, because they would then be able to sell their more expensive insecticides.
DDT’s effectiveness at eradicating malaria has been proven time and time again. Various factors contribute to its usefulness in malaria control such as its long effective action, its strong repellency action, and its capability of being sprayed at specific times of the year before seasonal disease peaks.
DDT to this date has the longest effective action out of the twelve insecticides recommended for indoor residual spraying (FAQ on DDT use for residual house spraying, WHO). Compared to the other insecticides which may require a house to be sprayed every two to three months, DDT only needs to be sprayed one to two times per year. This not only sufficiently reduces the costs of the IRS program, but also the number of times a home has to be entered by trained sprayers.
The topic of resistance is understandably of great concern to all public health policymakers. Incidentally, resistance to DDT is primarily caused by agricultural crop protection, which has been outlawed since 1972 (Bate 2007), and will continue to be outlawed in accordance with our policy. In addition, there is evidence that suggests even mosquitoes containing the resistance factor may be adversely affected by DDT in indoor residual spraying. In an experiment comparing three insecticides’ toxicity, irritancy, and repellency actions, DDT proved to have the strongest repellency action out of the three, even though the mosquito species used in the experiment was genetically resistant to only DDT (Grieco et. al. 2007). Although DDT is less toxic than other insecticides, the chemical's strong repellency action means that “DDT basically functions as a form of chemical screening, which stops mosquitoes from entering houses and transmitting malaria. . . To date, a truly efficacious DDT replacement has not been found and one may never be found because of the true nature in which DDT functions” (Grieco et. al. 2007).
Insecticide-treated nets may be the closest we have come to a safe and effective alternative to indoor residual spraying with DDT. However, a few factors still make IRS with DDT superior to insecticide-treated nets. Nets can offer a more discriminating screen from malaria-causing mosquitoes, but residents are only protected as they lie in their beds. In addition, nets offer little or no repellency action, so mosquitoes will likely still enter the home. In cases of sudden outbreaks of malaria or typhus in developing countries, there is no time (or political stability) to educate the home residents how to effectively use their insecticide-treated nets. Indoor residual spraying, on the other hand, can be done quickly and efficiently by trained emergency professionals.
Ecology and Natural Resources
There has been much speculation about the effects of DDT on the environment. However, the effects on the environment have not been confirmed (Roberts, Manguin and Mouchet 2000). The effects on soil and water resources are minimal. The most common of these are persistence, distribution and accumulation. These effects are primarily due to a great deal of DDT being introduced into the environment. The amount of DDT introduced into the environment depends upon the use of the pesticide. When it is used for agricultural purposes, the pesticide is sprayed in high levels and over a greater area. However, when DDT is used for residual house spraying, the levels are much lower and more confined. With a ban on the agricultural use of DDT, the pesticide will be used only for public health control and, therefore, introduced only into a small area and only in an enclosed space (Roberts, Manguin and Mouchet 2000).
There have also been many accusations that DDT has negative effects on wildlife, most notably birds. The most commonly known alleged effect of DDT on birds if the thinning of eggshells and, as a result, the death of chicks and reduction in population of different types of birds. In reality, there have been numerous studies proving that DDT has little, if any, affect on the thickness of eggshells. A study conducted by Bitman showed that DDT only affected eggshells when the level of calcium in the birds’ diet was well below the normal level of 2.5 percent. Thinning of eggshells was seen at a level of .56 percent calcium but not at a level of 2.7 percent (Edwards 2004). The speculation that populations of birds decreased due to the use of DDT is untrue. Many counts have been done that prove that the population of many types of birds increased during the time that DDT was being used (Edwards 2004). In addition, the claims that ingestion of DDT by birds can kill them have been proven to be false. One study found that even extremely high levels of DDT in food did not severely poison birds (Edwards 2004).
The claims that DDT negatively affects marine wildlife have also been questioned. An article written by Paul Ehrlich describing an experiment performed by Charles Wurster claimed that marine algae died due to levels of 500 ppb DDT. Since DDT is only soluble at a level of 1.2 ppb, he was questioned as to how he could have achieved such high levels. In response, he admitted that he had added enough alcohol to achieve the desired results (Edwards 2004). Since these conditions are unlike those found in a normal marine environment, these findings can be discounted.
The primary effect of DDT on other wildlife is food web accumulation. Food web accumulation occurs when animals ingest DDT and then get consumed by other animals higher up the food chain (Williams, 1970). Since DDT is stored in fat, the levels of the pesticide found in animals lower in the food chain get passed along to high-order carnivores (Moore, 1967). This means that the animals further along the food web, accumulate higher levels of DDT and, therefore, experience complications linked to the pesticide. However, this food web accumulation occurs only when high levels of DDT are introduced directly into the environment. With a ban on agricultural spraying the levels of DDT in the environment will be much lower. Therefore, DDT will accumulate much more slowly and will not be seen in high levels in animals. This will greatly reduce the complications seen in animals that have been linked to DDT consumption.
Human Health Concerns
It is known that humans are exposed to pesticide contamination through drinking water, dermal exposure, inhalation, and ingestion. The EPA has stated that current levels of DDT pesticidal residues do not pose any negligible health risks to human populations. Additionally, the risk of cancer from DDT exposure has not been stated as a substantive threat to human health (EPA). Other pesticides including agricultural herbicides (Atrazine, Metalochlor, Cyanozine, Alachlor, Acetochlor) and urban herbicides (Simazine, Prometon, Tebuthiuron, 2,4-D, and Diuron) and insecticides (Diazinon, Chloropyrifos, Carbaryl) have created concern for their potential to negatively impact human health with acute and long-term effects (Gilliom). From simple irritation and flu-like symptoms to more significant, long-term effects on the brain and nervous system, reproductive functions, vitality of organs, endocrine emitters, and risks of cancer and tumors(EPA). These pesticides are found in measurable amounts within water sources, the air, and soil. DDT has not been directly linked to cancer, chronic health effects, or fatality; this suggests that pesticidal substitutes for DDT have had more substantial and numerous impacts on human health than studies on DDT have shown.
Recently, some members of the scientific community have expressed additional criticism to claims of DDT’s negative effects. Opposition to Rachel Carson’s Silent Spring
(1962) have brought attention to many discrepancies in Carson’s argument against the use of DDT. First, Carson claims that DDT has carcinogenic effects on humans; however, after reviewing the original experiment performed, several errors were brought to light. The food given to the rats being observed was moldy and contained aflatoxin, a known carcinogen. When the tests were repeated using non-contaminated foods, there were no cases of tumors developing (as reported in previous study). Industrial workers and farmers that have worked in close contact or with DDT (i.e. Montrose Chemical Company) have not, to this day, shown signs of cancerous developments related to DDT exposure. It is important to note that African nations continually attribute the use of the chemical DDT as a crucial preventative factor to malaria disease, a move that has protected the lives of roughly 500 million people. In fact, there are some positive health impacts: DDT ingestion induces hepatic microsomal enzymes, which destroy carcinogenic aflatoxins and there by inhibit tumors and promote a healthy liver. Increased estrogen is also a common characteristic of DDT exposure; however, these levels were 40% less than the natural estrogenic pesticides. As part of this DDT defense, the scientific community has put many falsehoods of Carson’s argument under careful observation. They found the statements about decreasing bird populations and thinning eggshells lacked any sound scientific evidence, and in some cases, created the opposite effect. (Edwards, 83-87)
There is substantial evidence proving that current pesticidal use (and resultant contamination) do, in fact, pose risks to human health. In fact most, if not all, pesticides can cause adverse health effects when exposed to levels above EPA’s set MCLs, or maximum contaminant level (EPA). The U.S. EPA and the National Fish and Wildlife Foundation released a publication outlining eleven of the most commonly used pesticides and their known health effects; many of which included carcinogenic effects, reproductive complications, damage to nervous system, and endocrine disruption (EPA). These pesticides and their adverse health effects are comparable to the claimed effects of DDT, and some of these claims are currently facing scrutiny from the scientific community. DDT’s use in disease prevention and its efficiency as an insecticide in agriculture give much cause for further research into the actual consequences of DDT use. Much more research is needed in this area in order to effectively assess the toxicity of DDT.
The prevalence of malaria varies wildly throughout the world. According to the CDC website on malaria (where all these figures come from), forty-one percent of the world’s population lives in areas where malaria is transmitted in parts of Africa, Asia, the Middle East, and Central and South America. There are at least one million deaths that occur every year because of malaria. At the end of 2004 there were around 3.2 billion people living in areas at risk of malaria transmission and 107 countries and territories. In 2002, malaria was the fourth cause of death in children in developing countries, after conditions occurring around the time of birth, lower respiratory infections, and diarrheal diseases. Malaria caused 10.7% of all children’s deaths in developing countries. There are between 350 and 500 million clinical episodes of malaria that occur every year. Approximately 60% of the cases of malaria worldwide and more than 80% of the malaria deaths worldwide occur in Africa south of the Sahara. In areas of Africa with high malaria transmission an estimated 990,000 people died of malaria in 1995 which breaks down to 2700 deaths per day and 2 deaths per minute. In Malawi in 2001 malaria accounted for 22% of all hospital admissions, 26% of all outpatient visits, and 28% of all hospital deaths (CDC).
There are two types of malaria as defined by the CDC website, uncomplicated malaria and severe malaria. Uncomplicated malaria, which is the most common, consists of attacks lasting 6-8 hours that consist of fever, chills, sweats, headaches, nausea and vomiting, body aches and general malaise. Diagnosis of malaria depends on the demonstration of parasites on a blood smear examined under a microscope. In P. falciparum malaria, additional laboratory findings may include mild anemia, mild decrease in blood platelets (thrombocytopenia), elevation of bilirubin, elevation of aminotransferases, albuminuria, and the presence of abnormal bodies in the urine (urinary "casts"). Severe malaria occurs when P. falciparum infections are complicated by serious organ failures or abnormalities in the patient's blood or metabolism. The manifestations of severe malaria include: cerebral malaria, with abnormal behavior, impairment of consciousness, seizures, coma, or other neurologic abnormalities, severe anemia due to hemolysis (destruction of the red blood cells), hemoglobinuria (hemoglobin in the urine) due to hemolysis, pulmonary edema (fluid buildup in the lungs) or acute respiratory distress syndrome (ARDS), which may occur even after the parasite counts have decreased in response to treatment, abnormalities in blood coagulation and thrombocytopenia (decrease in blood platelets) and cardiovascular collapse and shock. Severe malaria occurs most often in persons who have no immunity to malaria or whose immunity has decreased. These include all residents of areas with low or no malaria transmission, and young children and pregnant women in areas with high transmission. In all areas, severe malaria is a medical emergency and should be treated urgently and aggressively (CDC).
Individual and Government Cost
Malaria is not only taxing on an individual’s and overall population’s health, it is detrimental to the economy. For an individual, the costs of malaria could include: expenses for travel to and also for treatment at clinics and dispensaries, the cost of drugs used for treatment of malaria, lost days and pay from work, absence from school, expenses for preventive actions, and also the cost of a burial should a death occur (CDC). Clearly, the burdens of malaria on an individual alone are extensive; however, even more substantial is the toll malaria takes on the government. Governmental costs of malaria include: purchase of drugs and healthcare supplies, maintenance of treatment facilities, public-health interventions, lost days of work, as well as lost joint economic ventures and tourism. These costs can add considerably to the economic burden of malaria, and in turn inhibit their economic growth and GDP (CDC). In a recent estimate, the economic growth per year of countries with endemic malaria was 1.3% lower than countries without a prominent malaria threat. (Gallup, Sachs)
Geography and Economic Impact
Malaria is most prominent in poor, subtropical and tropical areas around the world. Africa, south of the Sahara, is shown to have the most intensive malaria problem, where an estimated 90% of deaths due to malaria take place (CDC). Though malaria is a geographically specific disease, and can be intensified by the efficiency of the disease vector, the severity of the strain of malaria, as well as the local climate, another intensifying factor is the socio-economic stability of the area infected (CDC). While malaria can thrive in continents such as Africa, the instability and poverty in the same areas is playing a major role in the extent of the damage due to the disease. In heavily burdened countries malaria accounts for up to 40% of public health expenditures, 30-50% of inpatient hospital admissions, and up to 60% of outpatient health clinic visits (Gallup, Sachs). In countries with a high level of poverty, malaria takes a higher toll as people who cannot afford treatment have limited access to health care. Consequently, families, communities, and countries are trapped in a downward spiral of poverty. It has been shown that with the eradication of malaria from an area, the GDP of that country begins to steadily increase. (Gallup, Sachs)
DDT Use Against Malaria
According to a journal article posted on the Malaria Foundation International website, using DDT for the eradication of malaria has been particularly effective in the past. With the earliest of field studies, DDT was shown to be a spectacular repellent, irritant, and toxin that worked against malaria vector mosquitoes (Roberts, Manguin and Mouchet 2000). House spraying produced rapid results in 1943 in the Mississippi Valley, USA, and then in Italy, Venezuela, Guyana, India and several other countries. This house-spraying initiative functioned as national malaria-eradication services. Most countries adopted the malaria-eradication strategy that was formulated and coordinated by WHO (Roberts, Manguin and Mouchet 2000). Colonial Africa wasn’t a part of this effort because of the lack of national structure and expertise. However, some African countries did start their own eradication programs involving DDT. Although DDT does not completely stop malaria transmission, especially in wet areas of West Africa, the overall effect of applying DDT to house walls was an almost complete reduction or elimination in other areas (Roberts, Manguin and Mouchet 2000). Malaria was eradicated from most of North America and Europe and there were strong decreases in the prevalence in the Mediterranean Basin, the Middle East, the Far East and even in Southern Africa (Roberts, Manguin and Mouchet 2000). The previous effects of DDT against malaria is a clear indicator of how important DDT can be as a disease control agent and how when implemented correctly it can have a huge impact on the health of a country.
Throughout the years many alternatives to the use of DDT have been proposed and often utilized. The foremost of these alternatives was the use of other insecticides that were considered to be less toxic. Organophosphate and carbamate insecticides, while requiring the same dosage as DDT to be effective, are more expensive than DDT. Pyrethroids can be applied less regularly than organophosphates and carbamate insecticides; however, they still remain more expensive than DDT (Curtis). Not only is DDT less expensive than most alternatives, but in most cases it lasts much longer, requiring less applications. It has also been proven that DDT not only kills mosquitoes but repels them, which delays pesticide-resistance in vectors (Rosenberg).
Other alternatives to the use of DDT have included further education of disease control in high risk areas, increased health care and anti-malarial medicine, and organized efforts to eliminate vector breeding sites (CDC). Several of these options are better served as additions to the use of DDT, instead of alternatives. Area’s where malaria is prevalent are most commonly impoverished or economically unstable, decreasing the possibility of an organized effort to eradicate disease vectors, as well as the ability to pay for increased health care. The use of DDT in these areas is quick, effective, and much easier to utilize. With the severity of the disease in many areas, action must be taken quickly to save lives.
Transmission of Typhus through Lice
DDT can help stop Typhus. How? By ridding areas that have bad sanitation of louse infestations. It is commonly known that Typhus is caused by the bacteria known as Rickettsia prowazeki, which is spread by the common body louse aka Pediculus humanus corporis. This bacterium is transferred to the human body when the feces or crushed body of the louse is rubbed into a bite wound, usually because of scratching and picking that common among those with Lice. They are most commonly found around the waistline, neck, groin, and armpits. The eggs, or “nits”, are glued to fibers in clothing or body hair by the female louse. Once the egg-laying process begins, the female will lay approximately 10 eggs a day for 20-30 days (Conlon). As lice require a temperature between 73.4 and 100.4 degrees Fahrenheit to survive, if the host dies, the lice must move on quickly or die themselves (Conlon). Likewise, the eggs themselves will not hatch for a longer period of time if the temperature drops (due to the host dying). Upon hatching, the young lice will begin feeding immediately, and live around 30 days once fully mature (Conlon). When lice feed upon a person with Typhus, the majority of them will become infected with the R. Prowazeki bacteria which multiply in the intestinal tract of the louse. R. Prowazeki will begin to appear in the feces 3-5 days after first infection, and will usually kill the louse after about 9 days (Conlon).
However, if the louse manages to survive, it is infectious for its entire life. Once endemic in a population, if the conditions are right Typhus can spread rapidly as the Lice travel from person to person. As it is solely a louse-bourne disease, it figures that the disease will be spread only in ideal situations for the louse. Generally, Typhus usually becomes epidemic when people are clustered together and there is a heavy lice population, the lice will spread rapidly as host scratching will cause them to “wander about and reach the outer surface of clothing, from which they may be readily transferred to other persons” (Conlon, P.5) So, in crowded slums, prisons, refugee camps, or during war time or a disaster of some kind, or when people are unable to bathe regularly lice are known to spread rapidly and efficiently. In these types of conditions, when sanitation is unavailable and personal hygiene is particularly low, DDT would be vastly useful in eliminating the lice, and thus, eliminating Typhus from vulnerable populations.
Typhus is a disease that could kill thousands in epidemic form. Typhus spreads easiest in cramped conditions with poor sanitation. These conditions typically happen in times of war or other emergency situations. DDT use in these situations is the fastest and cheapest type of control because of the application by spraying the person.
It is true that Typhus is well controlled in most situations. Also, DDT use for the disease’s control is the third best control method. The first best control method is simple sanitation. This disease is spread by Pediculus Humanus corporis, a type of lice and can be controlled by washing your body, clothes, and house. The second best method for controlling the disease is to attack the cause. Typhus is caused by the infection called Rickettsia Prowazekia. This infection does have vaccine that was developed in 1938. In other words, in perfectly stable conditions Typhus is easily controlled without the use of DDT. The problem is that many places in the world are not stable and cannot get the vaccine. In times of war or emergences the best way to get rid of this disease is to kill the lice with DDT.
In history the worst cases of Typhus outbreaks have occurred during war. The first ever reported case of epidemic Typhus happened in 1489 during a Spanish siege of Granada. The men were in cramped and disgusting conditions. The conditions were ripe for the body lice and the disease that they carry. The best documented success in controlling a Typhus outbreak happened during WWII.
At the height of WWII an alarming outbreak started in the Italian city of Naples. If the disease had been allowed to proceed unchecked, the whole cities population would have been threatened. The army decided that DDT dusting would be the easiest route to controlling the disease. By dusting the people and all of their belongings the disease was stopped. During this outbreak and others that happened in Japan, strength tests were conducted on DDT and other pesticides.
The findings about the effectiveness of DDT compared to others pesticides were less than exciting. DDT was found on average to be half as affective as other ones. Why then is DDT still thought of as being the best pesticide available to the control of this disease? The answer to that question is simple. The reason that DDT is not as effective as the other pesticides is because it is not as toxic. This fact allows for DDT to be safe enough to use on people.
The last thing to remember about Typhus is the fact that the bugs that transmit the disease live on the person. This means that the pesticide treated nets used to fight Malaria could not prevent the spread of typhus. Either you would carry the lice into the nets with you or you would just get the disease when you went out of the net. Because of the conditions that make typhus outbreaks possible DDT is the best and easiest way to stop an outbreak in its tracks.
In order to continue using DDT for disease vector control in a responsible manner, what needs to change? First of all, there would have to be some alterations and additions to the current United Nations policy and regulations on DDT. Use itself would be more regulated, but acquiring it would be somewhat easier. Areas that are at a high risk for either Malaria or Typhus, as well as areas in emergency situations, would be able to acquire DDT for disease vector control. The use of DDT by these areas would be monitored by the United Nations. Nations that cannot afford to synthesize or purchase their own DDT, as well as areas in emergency situations, would have DDT provided by the UN. In the case of a stable government, the local government would be allowed to handle public spraying, while in the case of unstable governments, a UN task force would. The United Nations would also make efforts to increase public education about the benefits of DDT in the hopes of persuading the public to allow Indoor Residual Spraying for their own protection against disease.
Despite its many current benefits, it is important to note that DDT is hard to monitor and is, by no means, the ultimate solution. The current Stockholm Convention fully recognizes that at some point, a better alternative will be discovered, eliminating the current necessity of DDT. Currently, however, the benefits of using DDT as disease vector control outweigh the costs, as long as said use is properly regulated.
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