The global use of DDT and alternative control strategies against malaria has been reviewed in an article published online in Environmental Health Perspectives. The review was commissioned for the Stockholm Convention on Persistent Organic Pollutants, an international treaty that plans to phase out the use of the chemical by 2020 over concerns about the long-term risks it poses to human health and the environment.

 

More attention needs to be given to the adverse effects of DDT in relation to the health gains from its use in malaria prevention, says Henk van den Berg, of Wageningen University in the Netherlands. “[T]he evidence base on some of the more serious and chronic health effects of DDT is growing.”

 

DDT is an insecticide that lingers in the environment for up to 12 years. It is sprayed inside buildings to discourage the mosquitoes that carry the malaria parasite from entering and kills the ones that do, protecting those inside from the disease. Research into the health effects of DDT exposure carried out in North America and Europe have suggested it can cause early foetal loss during pregnancy, lower fertility, problems with brain development, diabetes, and several types of cancer.

 

The Stockholm Convention, signed by 152 countries, came into effect in 2004 and aims to protect human health and the environment from dangerous, long-lasting chemicals. The agreement hopes to stop the production and use of DDT by 2020. Under the guidance of the World Health Organization (WHO), the treaty allows countries to use DDT for disease control where other methods are not available.

 

Van den Berg says between four and five thousand tonnes of DDT are used every year for disease control. “Ironically, DDT use in Africa has increased since the Convention came into effect,” writes the author. Fourteen countries still use DDT to control malaria and leishmaniasis, a parasitic disease spread by sand flies, with several more countries preparing to re-introduce the chemical, he says.

 

 

The full impact of DDT on human health is not known. No global assessment of the health risks associated with spraying the chemical indoors has been done because data are insufficient, says van den Berg. Some preliminary research suggests that coming into contact with the chemical in this way is associated with impaired semen quality, he adds. Most of the evidence into harmful effects of DDT comes from populations exposed to far lower levels of the chemical than those that might occur when it is used for indoor spraying.

Although authorities are concerned about the harmful effects of DDT, any actions aimed at reducing exposure to the pesticide must be weighed against the scale of human illness caused by malaria. If the use of DDT is reduced, or the chemical is replaced by other pesticides, the alternative control methods must be just as effective at controlling the disease, the WHO said last month in a press statement.

 

Margaret Chan, Director-General of the WHO, described the task of sustainably reducing the toll of vector-borne diseases like malaria and the use of DDT as a “double challenge”.

 

 

Currently, 11 insecticides other than DDT are recommended  for indoor spraying. In some parts of the world mosquitoes have developed resistance to some of these DDT alternatives, says van den Berg. No new insecticides are expected to be developed any time soon, he adds. Recent EU legislation may further discourage the manufacture of suitable alternatives, experts have suggested.

 

Insecticide resistance is also a concern for communities that use DDT. The number and size of malaria-prevention schemes that use the chemical for indoor spraying is expanding in Africa as a result of the global community’s renewed focus on reducing malaria burden in recent years, explains van den Berg.

 

This expansion brings with it growing concerns about mosquitoes developing resistance to the pesticide, he says, which could have far-reaching consequences. “To be prepared for future emergencies, the continued effectiveness of insecticides needs to be safeguarded.”

 

 

Several malaria-prevention strategies do not use chemicals to control mosquitoes that spread the disease. Instead, these initiatives take different approaches such as improving housing quality, changing the habitat of mosquitoes, and destroying those places where they breed, says van den Berg.

 

The fall in malaria transmission achieved in some African countries as a result of strategies that include indoor spraying of DDT could now enable these non-chemical methods to take centre stage in the fight against malaria, explains van den Berg. This could, in turn, reduce the world’s reliance on pesticides.

 

But the effectiveness of non-chemical methods remains unclear, highlights van den Berg in the report. Integrating such measures into malaria management programmes requires the continued development of new technologies, he adds.

Last month the WHO and the United Nations Environment Programme released details of a five-year pilot trial of pesticide-free malaria management in Mexico and Central-American countries. The number of people with the disease fell by more than 60% after the pesticide-free initiatives were introduced.

 

The pesticide-free projects are now going global, with similar schemes to be launched several countries in North and East Africa, Central Asia and the Middle East, according to the WHO.