User:Yilloslime/DDT and Malaria

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[edit] DDT use against malaria

As discussed above, DDT was initially developed to control the insect vectors of diseases like malaria and typhus, but its use quickly spread to agriculture. While agricultural use has since been banned, its use against malaria continues to this day in some parts of the world. The World Health Organization estimates that there are between 300 million and 500 million cases of malaria every year, resulting in more than 1 million deaths, with about 90% occurring in Africa, and mostly to children under the age of 5. [1]

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Most prior use of DDT was in agriculture, but the controlled use of DDT continues to this day for the purposes of public health. Current use for disease control requires only a small fraction of the amounts previously used in agriculture, and at these levels the pesticide is much less likely to cause environmental problems. Residual house spraying involves the treatment of all interior walls and ceilings with insecticide, and is particularly effective against mosquitoes, which favour indoor resting before or after feeding. Advocated as the mainstay of malaria eradication programmes in the late 1950s and 1960s, DDT remains a major component of control programmes in southern African states, though many countries have abandoned or curtailed their spraying activities. South Africa, Swaziland, Mozambique and Ecuador are examples of countries that have very successfully reduced malaria infestations with DDT.

Indeed, the problems facing health officials in their fight against malaria neither begin nor end with DDT. Experts tie the spread of malaria to numerous factors, including a chronic lack of funds in the countries worst hit by malaria, and the resistance of the malaria parasite itself to the drugs traditionally used to treat the illness.[2] According to Richard Tren, "Malaria surged through Africa in the 1990s, fueled by resistance to chloroquine and other historically effective drugs."[3]

The growth of resistance to DDT and the fear that DDT may be harmful both to humans and the environment led donor countries and various national governments to restrict or curtail the use of DDT in vector control. At the same time, use of DDT as an agricultural insecticide was often unrestricted, and restrictions were often evaded, especially in developing countries where malaria is rife, so that resistance continued to grow.[4]

A commentary on the current state of global malaria control was published in the May 2007 issue of the Journal of the American Medical Association. The authors identify "3 critical factors that are currently absent or in too short supply" for making progress in the fight against malaria: "leadership, management, and money," while making no mention of restrictions limiting the use of DDT. They also single out resistance of the malaria parasite to chloroquine as the cause of increasing malaria mortality in sub-Saharan Africa, not restrictions on DDT.[5]

Today there is debate among professionals working on malaria control concerning the appropriate role of DDT. The range of disagreement is relatively narrow: Few believe either that large scale spraying should be resumed or that the use of DDT should be abandoned altogether. The debate focuses on the relative merits of DDT and alternative pesticides as well as complementary use of interior wall spraying, insecticide-treated bed-nets, and other mosquito control techniques.

Since the appointment of Arata Kochi as head of its anti-malaria division, the WHO has shifted its position in this controversy, from primary reliance on bed-nets to a policy more favorable to DDT. Until an announcement made on 16 September 2006, the policy had recommended indoor spraying of insecticides in areas of seasonal or episodic transmission of malaria, but a new policy also advocates it where continuous, intense transmission of the disease causes the most deaths.[6] In 2007, the WHO clarified its position, saying it is "very much concerned with health consequences from use of DDT" and reaffirmed its commitment to phasing out the use of DDT.[7]

[edit] Overall effectiveness of DDT against malaria

In the period from 1934-1955 there were 1.5 million cases of malaria in Sri Lanka, resulting in 80,000 deaths. After the country invested in an extensive anti-mosquito program with DDT, there were only 17 cases reported in 1963. Thereafter the program was halted, and malaria in Sri Lanka rebounded to 600,000 cases in 1968 and the first quarter of 1969. Although the country resumed spraying with DDT, many of the local mosquitoes had acquired resistance to DDT in the interim, presumably because of the continued use of DDT for crop protection, so the program was not nearly as effective as it had been before. Switching to the more-expensive malathion in 1977 reduced the malaria infection rate to 3,000 by 2004. A recent study notes, "DDT and Malathion are no longer recommended since An. culicifacies and An. subpictus has been found resistant."[8]

A 2004 editorial in the British Medical Journal argues that the campaign against malaria is failing, that funding of malaria control should therefore be increased, and that use of DDT should be considered since DDT has "a remarkable safety record when used in small quantities for indoor spraying in endemic regions."[9]

One insecticide supply company states on its website:

DDT is still one of the first and most commonly used insecticides for residual spraying, because of its low cost, high effectiveness, persistence and relative safety to humans. [...] In the past several years, we supplied DDT 75% WDP to Madagascar, Ethiopia, Eritrea, Sudan, South Africa, Namibia, Solomon Island, Papua New Guinea, Algeria, Thailand, and Myanmar for Malaria Control project, and won a good reputation from WHO and relevant countries' government.[10]

According to DDT advocate Donald Roberts, malaria cases increased in South America after countries in that continent stopped using DDT.[11] Other mosquito-borne diseases are also on the rise. Roger Bate claims that until the 1970s, DDT was used to eradicate the Aedes aegypti mosquito from most tropical regions of the Americas. The reinvasion of Aedes aegypti since has brought devastating outbreaks of dengue fever, dengue hemorrhagic fever, and a renewed threat of urban yellow fever.[12]

[edit] Mosquito resistance to DDT

Although the publication of Silent Spring undoubtedly influenced the U.S. ban on DDT in 1972, the reduced usage of DDT in malaria eradication began the decade before because of the emergence of DDT-resistant mosquitoes. Paul Russell, a former head of the Allied Anti-Malaria campaign, observed in 1956 that eradication programs had to be wary of relying on DDT for too long as "resistance has appeared [after] six or seven years."[13]

In some areas DDT has lost much of its effectiveness, especially in areas such as India where outdoor transmission is the predominant form. According to one article by V.P. Sharma, "The declining effectiveness of DDT is a result of several factors which frequently operate in tandem. The first and the most important factor is vector resistance to DDT. All populations of the main vector, An. culicifacies have become resistant to DDT." In India, with its outdoor sleeping habits and frequent night duties, "the excito-repellent effect of DDT, often reported useful in other countries, actually promotes outdoor transmission."[14]

Due to this DDT resistance, in Sri Lanka, parts of India, Pakistan, Turkey and Central America, DDT has already been replaced by organophosphate or carbamate insecticides, e.g. malathion or bendiocarb. [15]

According to a pesticide industry newsletter, DDT is obsolete for malarial prevention in India not only owing to concerns over its toxicity, but because it has largely lost its effectiveness. Use of DDT for agricultural purposes was banned in India in 1989, and its use for anti-malarial purposes has been declining. Use of DDT in urban areas of India has halted completely. Food supplies and eggshells of large predator birds still show high DDT levels.[16] Parasitology journal articles confirm that malarial vector mosquitoes have become resistant to DDT and HCH in most parts of India.[17] Nevertheless, DDT is still manufactured and used in India.[18] One study concludes "The overall results of the study revealed that DDT is still a viable insecticide in indoor residual spraying owing to its effectivity in well supervised spray operation and high excito-repellency factor."[19]

The initial appearance of this resistance was largely due to the much greater quantity of DDT which had been used for agricultural spraying, rather than the relatively insignificant amounts used for disease prevention. According to one study which attempted to quantify the lives saved due to banning agricultural use of DDT and thereby slowing the spread of DDT resistance: "Correlating the use of DDT in El Salvador with renewed malaria transmission, it can be estimated that at current rates each kilo of insecticide added to the environment will generate 105 new cases of malaria."[4]

Advocates for continuing use of DDT against malaria state that "Limited use of DDT for public health has continued to be effective in areas where it is used inside homes. As DDT's chief property is repellency, mosquitoes often avoid the DDT treated homes altogether. In so doing, they avoid the exposure that promotes resistance as well. DDT resistance exists in West Africa and in other malarial areas, such as India. Isolated occurrences of DDT resistance have occurred in South Africa, and South Africa continues to monitor for resistance. As the various Departments of Health that use it carefully control DDT use, it is unlikely that resistance will emerge as a major problem."[20]

Studies of malaria-vector mosquitoes trapped while exiting windows in KwaZulu-Natal Province, South Africa found susceptibility to 4% DDT (the WHO susceptibility standard), in 63% of the samples, compared to the average of 86.5% in the same species caught in the open. The authors concluded that "Finding DDT resistance in the vector An. arabiensis, close to the area where we previously reported pyrethroid-resistance in the vector An. funestus Giles, indicates an urgent need to develop a strategy of insecticide resistance management for the malaria control programmes of southern Africa." [21]

The avoidance of DDT-sprayed walls by mosquitoes is sometimes touted as a beneficial aspect of DDT.[19] For example, a 2007 study published in PLoS ONE reported that DDT-resistant mosquitoes still avoided DDT-treated huts, while entering huts treated with other insecticides to which they were not resistant. The researchers argued that DDT was the best pesticide for use in IRS (even though it did not afford the most protection from mosquitos out of the three test chemicals) because the others pesticides worked primarily by killing or irritating mosquitoes—modes of action the authors presume mosquitoes will develop resistance to.[22] Others have argued that the avoidance of DDT sprayed walls by mosquitoes is detrimental to the actual eradication of the disease.[23] Unlike other insecticides such as pyrethroids, DDT requires a long period of contact before mosquitoes pick up a lethal dose; however its irritant property makes them fly off before this occurs. "For these reasons, when comparisons have been made, better malaria control has generally been achieved with pyrethroids than with DDT." [15]

[edit] Residents' resistance to use of DDT

In areas where resistance from residents prevents a high percentage of the homes being effectively sprayed, the effectiveness of the intervention is greatly reduced.[15][13] Many residents resist spraying of DDT for various reasons. For instance, the smell lingers,[24] and DDT leaves a stain on the walls.[25][23][15][24][26] While that stain makes it easier to check whether the room has been sprayed it causes some villagers to avoid spraying of their homes [13][26][27][15] or to resurface the wall, which eliminates the residual insecticidal effect of the spraying.[23][26][27] "Pyrethroids such as deltamethrin and lambda-cyhalothrin are … much more acceptable to householders because they leave no visible deposit on walls… therefore rates of refusal of spraying by householders are lower with pyrethroids than with DDT."[15]

In addition, DDT is not suitable for this type of spraying in Western-style plastered or painted walls, only traditional dwellings with unpainted walls made of mud, sticks, dung, thatch, clay, or cement.[21][24][27][26]As rural areas of South Africa become more prosperous, there is a shift towards Western style housing, leaving fewer homes suitable for DDT spraying, and necessitating the use of alternative insecticides.[27]

Other villagers object to DDT spraying because it does not kill cockroaches[15] or bedbugs;[23] rather, it excites such pests making them more active,[24][27][26][25][13] so that often use of another insecticide is additionally required.[27] Pyrethroids such as deltamethrin and lambdacyhalothrin, on the other hand, are more acceptable to residents because they kill these nuisance insects as well as mosquitoes.[15] DDT has also been known to kill beneficial insects, such as wasps that kill caterpillars that, unchecked, destroy thatched roofs.[13]

As a result, says Dr. Avertino Barreto, chief of infectious disease control in Mozambique, resistance to DDT spraying is "homegrown", not due to "pressure from environmentalists". "They only want us to use DDT on poor, rural black people," he says. "So whoever suggests DDT use, I say, 'Fine, I'll start spraying in your house first.' "[24]

[edit] Human exposure associated with DDT spraying for disease vectors

In the low income areas where malaria eradication is necessary, it is almost impossible to ensure that DDT intended for disease prevention does not get diverted to use on crops, on a totally unregulated basis. "The consequent insecticidal residues in crops at levels unacceptable for the export trade have been an important factor in recent bans of DDT for malaria control in several tropical countries".[15] Adding to this problem is a lack of skilled personnel and supervision.[23]

Evidence for exposure to DDT is seen in South Africa[28][29], where in contrast to areas where DDT use has ceased (even where it was used heavily), in areas where DDT is currently in use ostensibly in small amounts for malaria prevention only, DDT levels in men and women were significantly higher than the allowable daily intake.[26] Breast milk from regions where DDT is used for malaria control contains enough DDT to greatly exceed the allowable daily intake of breast feeding infants.[30][31] These levels have been associated with neurological abnormalities in babies ingesting relatively large quantities of DDT in their milk[15] although toxicity via this mode of intake has not been proved.[26]

Some researchers have suggested that the negative health effects of exposure to DDT might outweigh the health benefits afforded by anti-malarial properties. For example, scientists with the US National Institute of Environmental Health Sciences argued in The Lancet that "Although DDT is generally not toxic to human beings and was banned mainly for ecological reasons, subsequent research has shown that exposure to DDT at amounts that would be needed in malaria control might cause preterm birth and early weaning, abrogating the benefit of reducing infant mortality from malaria...DDT might be useful in controlling malaria, but the evidence of its adverse effects on human health needs appropriate research on whether it achieves a favourable balance of risk versus benefit."[32]

[edit] Criticism of restrictions on DDT use

There are claims that restrictions on the use of DDT in vector control have resulted in substantial numbers of unnecessary deaths due to malaria. Estimates for the number of deaths that have been caused by an alleged lack of availability of DDT range from hundreds of thousands, according to Nicholas Kristof,[33] to much higher figures. Robert Gwadz of the National Institutes of Health said in 2007 that "The ban on DDT may have killed 20 million children."[34] Paul Driessen, author of Eco-Imperialism: Green Power, Black Death,[35] argues that the epidemic of malaria in Africa not only takes the lives of 2 million people a year, but leaves those who survive malaria unable to contribute to the economy while sick and more vulnerable to subsequent diseases that might kill them.

These arguments have been called "outrageous" by former WHO scientist Socrates Litsios, and May Berenbaum, a professor of entomology at the University of Illinois at Urbana-Champaign, says that "to blame environmentalists who oppose DDT for more deaths than Hitler is worse than irresponsible."[36] In May 2008 article in Prospect, John Quiggin and Tim Lambert write that "the most striking feature of the claim against Carson is the ease with which it can be refuted."[37]

It has been suggested that DDT treatments were used long enough to eliminate insect-borne diseases in the West, but now that it is only needed in poorer nations in Africa, Asia and elsewhere, it has been banned or otherwise restricted. Some environmental groups have been strongly criticized for trying to ban all use of DDT. According to Amir Attaran, many environmentalist groups fought against the public health exception of DDT in the 2001 Stockholm Convention, against the objections of third world governments and many malaria researchers. "Greenpeace, World Wildlife Fund, Physicians for Social Responsibility and over 300 other environmental organizations advocated for a total DDT ban, starting as early as 2007 in some cases."[38] In an opinion piece in Nature Medicine he strongly objected to what would have been a de facto ban and stated: "Environmentalists in rich, developed countries gain nothing from DDT, and thus small risks felt at home loom larger than health benefits for the poor tropics. More than 200 environmental groups, including Greenpeace, Physicians for Social Responsibility and the World Wildlife Fund, actively condemn DDT for being "a current source of significant injury to...humans."[39]

Criticisms of a ban on DDT often refer specifically to the 1972 US ban (with the implication that this constituted a worldwide ban), while ignoring that DDT has not been banned for public health use in most areas of the world where malaria is endemic.[40] Reference is also often made to Rachel Carson's Silent Spring even though she never pushed for a ban on DDT. In fact, she devoted a page of the book to consideration of the relationship between DDT and malarial mosquitoes, with cognizance of the development of resistance in the mosquito, concluding:

It is more sensible in some cases to take a small amount of damage in preference to having none for a time but paying for it in the long run by losing the very means of fighting [is the advice given in Holland by Dr Briejer in his capacity as director of the Plant Protection Service]. Practical advice should be "Spray as little as you possibly can" rather than "Spray to the limit of your capacity."

However, the fact that DDT is not formally banned in developing nations does not necessarily mean that those nations have the option to use it. Developing nations are typically heavily dependent on aid from agencies that made the aid contingent upon non-usage of DDT. The British Medical Journal of March 11, 2000, reports that the use of DDT in Mozambique "was stopped several decades ago, because 80% of the country's health budget came from donor funds, and donors refused to allow the use of DDT."[41] Many African nations have been dissuaded from to using DDT in part because the European Union has said that their agricultural exports may not be accepted if spraying was "widespread."[42]

According to the USAID website, "USAID has never had a “policy” as such either “for” or “against” DDT for IRS. The real change in the past two years has been a new interest and emphasis on the use of Indoor Residual Spraying (IRS) in general – with DDT or any other insecticide – as an effective malaria prevention strategy in tropical Africa."[43] But the pro-DDT advocacy group Africa Fighting Malaria maintains that USAID and some other international donor organizations have refused to fund public health DDT programs.[44] Similarly, Roger Bate of AFM asserts that many countries have been coming under pressure from international health and environment agencies to give up DDT or face losing aid grants, and that Belize and Bolivia have gone on record to say that they gave in to pressure on this issue from the US Agency for International Development.[45] USAID's Kent R. Hill states that the agency has been misrepresented:

USAID strongly supports spraying as a preventative measure for malaria and will support the use of DDT when it is scientifically sound and warranted.[46]

However, USAID "favored" DDT alternatives in its funding:

Contrary to popular belief, USAID does not "ban" the use of DDT in its malaria control programs. From a purely technical point of view in terms of effective methods of addressing malaria, USAID and others have not seen DDT as a high priority component of malaria programs for practical reasons. In many cases, indoor residual spraying of DDT, or any other insecticide, is not cost-effective and is very difficult to maintain. In most countries in Africa where USAID provides support to malaria control programs, it has been judged more cost-effective and appropriate to put US government funds into preventing malaria through insecticide-treated nets, which are every bit as effective in preventing malaria and more feasible in countries that do not have existing, strong indoor spraying programs.[47]

[edit] Alternatives to DDT

[edit] DDT versus other insecticides

Those who advocate for increased use of DDT claim that the alternatives to DDT are generally more expensive, more toxic to humans and not always as effective at controlling malaria and insect-borne diseases, and that the petrochemical companies which patent those alternatives push(ed) for DDT's ban simply for their own profits; DDT had entered the public domain, their patented insecticides have not. Actual data on the cost-effectiveness of DDT versus other insecticides and/or means of fighting malaria is, in fact, lacking. One complicating factor is that the relative costs of various measures vary, depending on geographical location and ease of access, the habits of the particular mosquitoes prevalent in each area, the degrees of resistance to various pesticides exhibited by the mosquitoes, and the habits and compliance of the population, among other factors.

Organophosphate or carbamate insecticides, e.g. malathion or bendiocarb, are considerably more expensive than DDT, and malathion requires more frequent respraying. Pyrethroids such as deltamethrin and lambdacyhalothrin are also more expensive than DDT, but due to their much greater coverage per unit weight, the net cost per house is about the same.[15]

There are some insecticide alternatives to DDT, including methoxychlor and pyrethroids. The environmental and health effects of alternatives are also under scrutiny. Under the Stockholm Convention, these are issue to be addressed when investigating and promoting alternative chemicals. A recent study has found that DDT as well as pyrethroid residues, such as permethrin and deltamethrin, were present in breast milk from a malaria controlled area in South Africa. The DDT was derived from malaria control, but the pattern of pyrethoid pollution indicated exposure via agricultural use, where mothers frequently work in cotton fields, as well as from domestic use of insecticide dusts in vegetable gardens.[48]

  1. ^ Cite error: Invalid <ref> tag; no text was provided for refs named Larson
  2. ^ Norton, Jim. The DDT Ban Myth. Info-pollution.com. Retrieved on 2006-03-15.
  3. ^ [Africa: One in Three Malaria Drugs Failing, AllAfrica, 6 May 2008
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  5. ^ Feachem RG, Sabot OJ (2007). "Global malaria control in the 21st century: a historic but fleeting opportunity". JAMA 297 (20): 2281–4. doi:10.1001/jama.297.20.2281. PMID 17519417. 
  6. ^ WHO | WHO gives indoor use of DDT a clean bill of health for controlling malaria
  7. ^ http://www.yubanet.com/artman/publish/article_56180.shtml
  8. ^ Briët, Olivier JT; Gawrie NL Galappaththy, Flemming Konradsen, Priyanie H Amerasinghe and Felix P Amerasinghe (2005). "Maps of the Sri Lanka malaria situation preceding the tsunami and key aspects to be considered in the emergency phase and beyond". Malaria Journal 4: 8. doi:10.1186/1475-2875-4-8. PMID 15676073. 
  9. ^ Yamey, Gavin (8 May 2004). "Roll Back Malaria: a failing global health campaign". BMJ 328: 1086-1087. doi:10.1136/bmj.328.7448.1086. PMID 15130956. 
  10. ^ Yorkool Chemical - Manufacturer/Supplier of DDT, pyrethroid, and microbial insecticides for Malaria Control. Retrieved on 2006-03-15.
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  12. ^ Bate, Roger (24 April 2001). Without DDT, malaria bites back. spiked-online.com. Retrieved on 2006-03-15.
  13. ^ Cite error: Invalid <ref> tag; no text was provided for refs named Gladwell
  14. ^ Sharma, V. P. (10 Devember 2003). "DDT: The fallen angel". Current Science 85 (11): 1532-1537. 
  15. ^ a b c d e f g h i j k Control of Malaria Vectors in Africa and Asia C.F.Curtis
  16. ^ Agarwal, Ravi (May 2001). "No Future in DDT: A case study of India". Pesticide Safety News. 
  17. ^ Sharma, V.P. (1999). "Current scenario of malaria in India". Parassitologia 41 (1-3): 349-53. PMID 10697882. 
  18. ^ Art Fisher, Mark Walker, Pam Powell. DDT and DDE: Sources of Exposure and How to Avoid Them (PDF). Retrieved on 2006-03-15.
  19. ^ a b [1][dead link]
  20. ^ Africa Fighting Malaria - Frequently Asked Questions
  21. ^ a b Hargreaves K, Hunt RH, Brooke BD, et al (2003). "Anopheles arabiensis and An. quadriannulatus resistance to DDT in South Africa". Med. Vet. Entomol. 17 (4): 417–22. doi:doi:10.1111/j.1365-2915.2003.00460.x. PMID 14651656. 
  22. ^ Grieco JP, Achee NL, Chareonviriyaphap T, et al (2007). "A new classification system for the actions of IRS chemicals traditionally used for malaria control". PLoS ONE 2 (1): e716. doi:10.1371/journal.pone.0000716. PMID 17684562. 
  23. ^ a b c d e Mabaso ML, Sharp B, Lengeler C (2004). "Historical review of malarial control in southern African with emphasis on the use of indoor residual house-spraying". Trop. Med. Int. Health 9 (8): 846–56. doi:10.1111/j.1365-3156.2004.01263.x. PMID 15303988. 
  24. ^ a b c d e In Malaria War, South Africa Turns To Pesticide Long Banned in the West, Roger Thurow, Wall Street Journal, July 26, 2001
  25. ^ a b DDT and Africa's war on malaria, BBC
  26. ^ a b c d e f g Malaria and the DDT Story
  27. ^ a b c d e f South Africa’s War against Malaria Lessons for the Developing World, Richard Tren and Roger Bate, Cato Institute
  28. ^ http://whqlibdoc.who.int/bulletin/1990/Vol68-No6/bulletin_1990_68(6)_761-768.pdf
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  33. ^ Kristof, Nicholas D. (March 12 2005). "I Have a Nightmare". New York Times: Section A, Page 15 , Column 1. 
  34. ^ Finkel, Michael, "Malaria," National Geographic, July 2007
  35. ^ Eco-Imperialism - Green Power. Black Death.
  36. ^ Rachel Carson's birthday bashing, Kirsten Weir, Salon.com, June 29, 2007, accessed July 1, 2007.
  37. ^ Rehabilitating Carson, John Quiggin & Tim Lambert, Prospect, May 2008.
  38. ^ Malaria Foundation International
  39. ^ Attaran A, Roberts DR, Curtis CF, Kilama WL (2000). "Balancing risks on the backs of the poor". Nat. Med. 6 (7): 729–31. doi:10.1038/77438. PMID 10888909. 
  40. ^ Dr Alan Lymbery and Professor Andrew Thompson, letter in the The Australian, February 2, 2004. [3]
  41. ^ Sidley P (2000). "Malaria epidemic expected in Mozambique". BMJ 320 (7236): 669. doi:10.1136/bmj.320.7236.669. PMID 10710569. 
  42. ^ US Department of State. U.S. Senator Does a "Slam Dunk" for Africa Malaria Day.
  43. ^ USAID Health: Infectious Diseases, Malaria, Technical Area, Prevention and Control, Indoor Residual Spraying.
  44. ^ Africa Fighting Malaria Frequently Asked Questions. Retrieved on 2006-03-15.
  45. ^ Bate, Roger (May 14 2001). "A Case of the DDTs: The war against the war against malaria". National Review LIII (9). 
  46. ^ Kent R. Hill (2005). USAID isn’t against using DDT in worldwide malaria battle. Retrieved on 2006-04-03.
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  48. ^ Bouwman H, Sereda B, Meinhardt HM (2006). "Simultaneous presence of DDT and pyrethroid residues in human breast milk from a malaria endemic area in South Africa". Environ. Pollut. 144 (3): 902–17. doi:10.1016/j.envpol.2006.02.002. PMID 16564119. “Even if the pyrethroids were at that stage not used for indoor residual application, the authors indicated that such use would result in pyrethoids being taken up by the mothers and excreted in breast milk, thereby exposing breast feeding infants.” 

[edit] DDT versus non-chemical vector control

Before DDT, malaria was successfully eradicated or curtailed in several tropical areas by removing or poisoning the breeding grounds of the mosquitoes or the aquatic habitats of the larva stages, for example by filling or applying oil to places with standing water. These methods have seen little application in Africa for more than half a century.[1]

The relative effectiveness of IRS (with DDT or alternative insecticides) versus other malaria control techniques (e.g. bednets or prompt access to anti-malarial drugs) varies greatly and is highly dependent on local conditions.[2]

A study by the World Health Organization released in January of 2008 found that mass distribution of insecticide-treated mosquito nets and artemisinin based drugs cut malaria deaths in half in Rwanda and Ethiopia, countries with very high malaria burdens. IRS with DDT was determined to not have played an important role in the reduction of mortality.[3]

Vietnam is an example of a country that has seen a continued decline in malaria cases after switching in 1991 from a poorly funded DDT-based campaign to a program based on prompt treatment, bednets, and the use of pyrethroid group insecticides. Deaths from malaria dropped by 97%.[4]

In Mexico, the use of a range of effective and affordable chemical and non-chemical strategies against malaria has been so successful that the Mexican DDT manufacturing plant ceased production voluntarily, due to lack of demand.[5] Furthermore, while the increased numbers of malaria victims since DDT usage fell out of favor would, at first glance, suggest a 1:1 correlation, many other factors are known to have contributed to the rise in cases.

A review of fourteen studies on the subject in sub-Saharan Africa, covering insecticide-treated nets, residual spraying, chemoprophylaxis for children, chemoprophylaxis or intermittent treatment for pregnant women, a hypothetical vaccine, and changing the first line drug for treatment, found decision making limited by the gross lack of information on the costs and effects of many interventions, the very small number of cost-effectiveness analyses available, the lack of evidence on the costs and effects of packages of measures, and the problems in generalizing or comparing studies that relate to specific settings and use different methodologies and outcome measures. The two cost-effectiveness estimates of DDT residual spraying examined were not found to provide an accurate estimate of the cost-effectiveness of DDT spraying; furthermore, the resulting estimates may not be good predictors of cost-effectiveness in current programmes.[6]

However, a study in Thailand found the cost per malaria case prevented of DDT spraying ($1.87 US) to be 21% greater than the cost per case prevented of lambdacyhalothrin-treated nets ($1.54 US),[7] at very least casting some doubt on the unexamined assumption that DDT was the most cost-effective measure to use in all cases. The director of Mexico's malaria control program finds similar results, declaring that it is 25% cheaper for Mexico to spray a house with synthetic pyrethroids than with DDT.[5] However, another study in South Africa found generally lower costs for DDT spraying than for impregnated nets.[8]

A more comprehensive approach to measuring cost-effectiveness or efficacy of malarial control would not only measure the cost in dollars of the project, as well as the number of people saved, but would also take into account the negative aspects of insecticide use on human health and ecological damage. One preliminary study regarding the effect of DDT found that it is likely the detriment to human health approaches or exceeds the beneficial reductions in malarial cases, except perhaps in malarial epidemic situations. It is similar to the earlier mentioned study regarding estimated theoretical infant mortality caused by DDT and subject to the criticism also mentioned earlier.[9]

A study in the Solomon Islands found that "although impregnated bed nets cannot entirely replace DDT spraying without substantial increase in incidence, their use permits reduced DDT spraying."[10]

A comparison of four successful programs against malaria in Brazil, India, Eritrea, and Vietnam does not endorse any single strategy but instead states "Common success factors included conducive country conditions, a targeted technical approach using a package of effective tools, data-driven decision-making, active leadership at all levels of government, involvement of communities, decentralized implementation and control of finances, skilled technical and managerial capacity at national and sub-national levels, hands-on technical and programmatic support from partner agencies, and sufficient and flexible financing."[11]

DDT resistant mosquitoes have generally proved susceptible to pyrethroids. Thus far, pyrethroid resistance in Anopheles has not been a major problem.[12]