It is one drug that has raised hue and cry just as much as it has saved lives. DDT, which is the short form of Dichlorodiphenyltrichloroethane has been used continually in public health programmes over the past 60 years. It has saved millions of lives from diseases such as malaria, typhus and yellow fever. Despite a public backlash in the 1960s, mainstream scientific and public health communities continued to recognise its utility and safety.
DDT's delisting for various uses in the United States in 1972 was a political, not scientific, judgement. After decades of extensive study and use, DDT has not been proven to be harmful to humans.
By 1997, its future looked bleak. Environmentalists were pushing for it to be banned worldwide, and its most articulate champion, the South African Department of Health, stopped using it. Surprisingly, DDT recovered its reputation, and last year the World Health Organisation (WHO) championed it again.
But the celebrations have been short-lived. The momentum to increase DDT use has stalled for lack of increased political and financial support. The first attempt to eradicate malaria in 1950s relied almost solely on the chemical DDT; the latest attempt probably will not. But until a cheap and effectual vaccine is available, DDT will still have a crucial role to play.
DDT was first synthesised by Othmar Zeidler in 1874, but it was not until the 1930s that a scientist working for a Swiss chemical company discovered its insecticidal properties. Paul Mueller happened upon it when looking for an insecticide to control clothes' moths. He sprayed a small amount of DDT into a container and noted the slow but sure way it killed flies. He wiped the container clean, but when he added new flies, they too died. He soon realised he had come across a persistent, powerful residual insecticide.
In 1898, Ronald Ross, a medical doctor stationed with the British army in India, discovered that mosquitoes transmit malaria. Shortly thereafter, a leading Italian zoologist, Giovanni Battista Grassi, identified the specific genus of mosquito (Anopheles) as responsible for transmitting the malaria-causing parasite. Insecticides, notably pyrethrum, had been used in malaria control prior to DDT. They were sprayed on the inside walls of houses where the Anopheles mosquito rests after feeding.
One of the significant limiting factors of this form of vector control — known as indoor residual spraying (IRS) — was that it is labour-intensive and therefore expensive, especially since the insecticides used before DDT had to be sprayed every two weeks. DDT, however, lasted for over six months.
When used in malaria control, DDT has three separate mechanisms: repellancy, irritancy, and toxicity, which together are remarkably successful at halting the spread of the disease.
By 1952, there were virtually no cases of malaria transmitted domestically in the US, in contrast to the between one to six million cases just a few years earlier.
In 1955, WHO launched its own malaria eradication programme, based on the extraordinary successes seen thus far with DDT. The programme was funded mostly by the US Government.
But Rachel Carson's 1962 book "Silent Spring" questioned the impact synthetic chemicals were having on the environment. Her argument was that DDT and its metabolites make bird eggshells thinner, leading to egg breakage and embryo death. Carson postulated that DDT would, therefore, severely harm bird reproduction, leading to her theoretical "silent spring". She also implied that DDT was a human carcinogen by telling anecdotal stories of individuals dying of cancer after having used DDT sprays in the recent past.
In 1971, after considerable pressure from environmentalist groups, the newly formed Environmental Protection Agency (EPA) held scientific hearings investigating DDT. The hearings lasted for more than eight months. The administrative law judge in charge of the hearings, Edmund Sweeney, ruled that DDT should remain available for use because it was not found to represent a cancer threat to humans, to cause mutations in humans, or to threaten the development of foetuses.
DDT was relatively benign, and the allegations against it did not stand up to scrutiny.
But Sweeney was overruled in 1972 by the administrator of the EPA, Mr William Ruckelshaus. The decision to cancel certain uses of DDT was essentially a political one without any grounding in good science.
Although many believe that DDT was banned after 1972, it actually was not. It continued to be used in emergencies for pest control, for which exemptions were granted by the federal government, and it is still available for public health use today.
Between 1997 and 2000, member states of the United Nations Environment Programme (Unep) negotiated the Stockholm Treaty on Persistent Organic Pollutants, with DDT as one of the "dirty dozen" chemicals targeted. Green groups wanted the chemical banned and set this year as the year for its demise. Ironically, because of the disastrous surge in malaria cases in South Africa, coupled with Johannesburg being chosen as the final negotiating location in December 2000, DDT was not banned; instead, it was to be phased out when "cost-effective alternatives" were available.
In 2000, the South African Department of Health reintroduced DDT. In just one year, malaria cases fell by nearly 80 per cent in KwaZulu-Natal province, which had been worst hit by the epidemic. DDT remains an essential part of South Africa's malaria control programme and the success of its use in that country has encouraged other countries in the region to follow suit.
Since the late-2005 turnaround at Usaid and the September last year statements from WHO about the benefits of DDT, no country has started to use it again. Uganda has come closest so far, but to no avail. Health department malaria experts in Kenya and Tanzania have shown interest that they would like to use DDT, but business continues as usual. This is not the fault of senior management at the PMI. But according to field sources the same cannot be said of all Usaid staff, many of whom are still upset at the decision taken in 2005 to promote DDT once again. Furthermore, Global Fund support is weak, and field reports indicate that its contractors in the field are not always supporters of DDT. Many other aid agencies are even worse, often actively opposing IRS, and DDT on the ground. The environmental movement continues to exaggerate the dangers of DDT. Some corporations go even further. Bayer actively discouraged the use of DDT in Uganda, citing a possible threat to the country's supply of food for export.
The UN is once again ramping up opposition to DDT use. At its third session, ending on May 4 "the Conference of the Parties of the Stockholm Convention requested its secretariat in collaboration with WHO and interested parties to develop a business plan for promoting a partnership to develop alternatives to DDT for disease vector control". Since there are many players who want to sell alternatives to DDT, the chemical has few champions, and since those represented in this group are no friends of DDT, the partnership is likely to be well-financed. It may prove to be the final nail in DDT's coffin. DDT is no panacea, but it has a better track record on malaria control than any other intervention.
The writer is a resident fellow at American Enterprise Institute.