DDT, one of the most studied insecticides, has again come under attack. In May 2009, Environmental Health Perspectives (EHP) published The Pine River Statement: Human Health Consequences of DDT Use. This Statement, authored by 15 scientists from the US and SA, summarises information on the health risks of DDT use and makes recommendations for public health policy.
This is not the first time that the chemical has been placed under the magnifying glass and found to have no adverse human health effects. Indeed anyone who reads the Pine River Statement cannot but conclude that there is no evidence that DDT is harmful to human health, though this doesn’t stop the authors from saying that it ‘may pose a risk for human populations’, which is hardly a definitive statement. At best this statement should prompt researchers to conduct further analysis. At worst it could cause a knee-jerk reaction that results in some large multilateral organisation condemning its use despite its proven track record for controlling death and disease in malaria endemic countries.
In September 2006, the WHOs Global Malaria Programme announced its firm support for the use of DDT in indoor residual spraying (IRS) programmes and called for an expansion of such efforts. IRS programmes entail the application of tiny amounts of insecticide on the inside walls of houses to protect occupants for up to one year from deadly malaria-carrying mosquitoes.
Prior to the 2006 WHO announcement, the US President’s Malaria Initiative (PMI) began actively supporting IRS programmes and procuring DDT for those countries that sought to use it, a policy which stands to this day. The decision of the WHO, the PMI policies, and those policies developed over many years by malaria control programmes, are based on the historic and contemporary evidence that DDT is a remarkably effective and safe public health insecticide. Evidence of associations between DDT and cancer in humans is weak. Indeed, according to the International Agency for Research on Cancer, DDT shares a classification as a potential carcinogen with a number of other everyday household consumables such as beer, coffee and peanut butter..
Yet in an apparent reversal, the WHO recently announced that in line with a goal of reducing reliance on DDT for public health purposes it would work with the United Nations Environment Programme (UNEP) and the Global Environment Facility (GEF) to combat malaria using “sustainable” (for which no definition is given) alternatives to DDT. The promotion of such non-chemical methods of malaria control as “sustainable”, in effect only sustains disease transmission and an intolerably high burden of malaria in poor countries. Through these statements the WHO in effect abdicates its role in formulating evidence-based public health policy and adopts an environmentalist agenda over the health interests of people living in malarial areas.
Malaria kills a child every thirty seconds in Africa. The majority of deaths world-wide, over a million each year, occur in children under the age of five and in pregnant women. Effective malaria control saves lives, prevents the trauma of unnecessary deaths in families, and improves local economies. Malaria sufferers have great difficulty in carrying out sustained work, which intensifies human misery and poverty in areas where the disease is prevalent. Malaria is thus not only a human tragedy; it’s an economic one as well. In malarial countries it is estimated that the disease reduces per capita economic growth by 1.3 percent per year. This equates to approximately $12 billion in forgone income.
DDT was first used in public health during World War II when it was widely used in both the European and Pacific theatres of war to control lice-spread typhus as well as other insect-borne diseases. The first major applications of DDT against malaria took place after WWII and with remarkable outcomes. To control malaria, DDT was primarily used in IRS programmes. The insecticides used in IRS can act in several ways. First, they can act as a spatial repellent, keeping mosquitoes out of houses, thereby working rather like a chemical screen. DDT is the only insecticide recommended for IRS that works as a spatial repellent compound. Insecticides can also act as a contact irritant, causing mosquitoes to exit houses sooner than they otherwise would. Lastly, insecticides can act as a toxicant, killing mosquitoes as they land on sprayed surfaces.
A great advantage of IRS over other community-based approaches to malaria control is that once the insecticide is sprayed on the walls, no additional work by residents is needed for it to be effective. In South Africa DDT was introduced in 1946, and where it was applied annual cases fell from 1,177 (1945-46) to just 61 by 1951. In 1996 South Africa stopped using DDT due to international pressures and the desire to try an alternative control mechanism. Shortly after this, SA had a massive malaria outbreak. There was an eight-fold increase in malaria deaths from 1996 to 1999. The number of malaria cases increased at a similar rate from 5,000 per annum to more than 60,000. However, in 2000, SA reintroduced indoor residual spraying with DDT, amidst international pressures to ban the insecticide, and the number of cases dropped by a remarkable 80 per cent.
There can be no disputing the extraordinary impact that DDT has made, and continues to make, in disease control programmes around the world. The remarkable degree to which DDT saved lives has allowed communities to grow and prosper contrary to the expectations of critics who argue that DDT is harmful to humans. Broadly, the concerns that DDT may be harmful to human health are not supported by any meaningful data on deaths or diseases as a consequence of coming into contact with DDT, and are further contradicted by evidence over many decades of reduced disease and rising populations wherever the chemical has been used.
Robust, evidence-based discussion and debate over the role of DDT and other man-made chemicals in malaria control is helpful. Further research into DDT could help focus attention on the long-term lack of investment in the search for legitimate replacement chemicals for DDT. Until viable replacements are found the WHO should support the ongoing use of DDT based on the scientific evidence of its continued effectiveness. The promotion of environmental management as an alternative to the use of insecticides undermines malaria control and ultimately endangers the lives of millions of people at risk from the disease, who continue to suffer in silence.
Author: Jasson Urbach is a director of the Health Policy Unit (a division of the Free Market Foundation) and of Africa Fighting Malaria. This article may be republished without prior consent but with acknowledgement to the author. The views expressed in the article are the author's and are not necessarily shared by the members of the Foundation.
HPU Feature Article / 01 September 2009