New international convention allows use of DDT for malaria control
Malaria-endemic countries can continue using dichlorodiphenyltrichloroethane (DDT) to help control malaria due to an exemption clause in a convention banning the controversial substance. The Stockholm Convention on Persistent Organic Pollutants which came into force on 17 May, following its ratification by 50 states, outlawed the use of 12 industrial chemicals dubbed the "Dirty Dozen," including DDT.
The exemption clause allows malaria-endemic nations to use DDT strictly for indoor residual wall spraying (IRS): a measure which contributed to slashing the number of malaria cases in South Africa from 64 622 in 2000 to 8016 last year
"Malaria is now at its lowest level in ten years," said Rajendra Maharaj, a specialist scientist working with South Africa's national malaria control programme. "We attribute that to DDT."
Under pressure from environmentalists, South Africa suspended DDT for IRS in 1996 after five decades of use and switched to another class of insecticide known as pyrethroids. But the 19992000 malaria epidemic in KwaZulu-Natal and neighbouring provinces prompted the government to revert to DDT for prevention and to introduce artemisinin-based combination therapy for treatment.
Other African nations, such as Eritrea, Ethiopia and Swaziland have continually used DDT for IRS in certain areas. China and India the main supplier of the insecticide are two other countries currently using DDT focally. Some other countries in eastern and southern Africa are considering the introduction of DDT as part of their malaria control operations in epidemic-prone areas. The United Nations Environment Programme estimates that about 25 countries will use DDT under exemptions from the DDT pesticide ban.
Recognizing the role of DDT in disease vector control, WHO helped lobby for the exemption provisions during negotiations on the content of the Stockholm convention in 2000. Allan Schapira of WHO's Roll Back Malaria department said that IRS is often more rapidly effective in controlling epidemics than insecticide-treated bed nets. However, "insecticide-treated bednets remain the recommended method in settings of intense, ongoing transmission where it is at least as effective and usually much more acceptable by the populations," said Schapira.
Junaid M. Seedat, Managing Director of the international non-profit organization, Massive Effort Campaign, which campaigns to raise awareness of developing country diseases, said WHO should be more active in promoting DDT for IRS rather than relying on insecticide-treated bed nets alone as a preventative tool.
However, Dr Kabir Cham, Senior Adviser with WHO's Malaria Policy and Strategy Team, said that insecticide-treated bed nets and IRS each have their specific roles in malaria control. "DDT is one of 12 insecticides approved by WHO for IRS, and like all of them it has certain advantages and disadvantages, which should be analysed in the local context to make the best choice," said Cham.
In 1935 DDT was discovered to be a highly effective insecticide which led to its widespread use as a general pesticide in agriculture. Its use for disease control began during the Second World War and became the main product used in global efforts, supported by WHO, to eradicate malaria in the 1950s and 1960s. According to WHO's booklet, "Frequently asked questions on DDT use for disease vector control," this campaign resulted in a significant reduction in malaria transmission in many parts of the world and was probably instrumental in eradicating the disease from Europe and North America.
However, following widespread concern over the environmental and health risks posed by the chemical's persistence in the environment long after its initial application, DDT was banned in the US in 1972 and later in other countries. According to WHO, although there is no direct link between DDT and any negative human health effect, there is growing evidence that it may disrupt reproductive and endocrine function.
The WHO booklet "Frequently Asked questions on DDT use for disease vector control," is available at: http://mosquito.who.int/docs/FAQonDDT.pdf