Fighting Malaria with Fewer Chemicals

In Yale Environment 360, Sonia Shah highlights a promising trend: communities in Mexico, China, Tanzania, and elsewhere are adopting non-chemical methods to control the populations of mosquitos that transmit malaria. They've seen their numbers of malaria cases drop, and dramatically reduced their use of the pesticide DDT.

In addition to the environmental health risks that DDT poses, its continued use often results in mosquitos becoming resistant to the pesticide - or, they can adapt to interventions like insecticide-treated bednets by changing the times and places in which they bite, which Shah reports has happened in Dar es Salam.

Here are some of the non-chemical approaches that Shah describes:

In Oaxaca, Mexico, malariologists found that the local malaria vector, Anopheles pseudopunctipennis, hatches from the still, algae-choked waters on the edges of streams, rarely flying more than 2 kilometers from its birthplace. And so, starting in 1999, they recruited volunteers in malarious communities to remove green algae and trash from the rivers and streams near their settlements.

... In Dar es Salaam, Tanzania, Anopheles gambiae lays its eggs in trash-blocked sewer drains, and so community workers there began a program of clearing drains and spreading the microbial insecticide Bacillus thuringiensis into sewers. "This was the lowest-hanging fruit of them all," says Gerry Killeen of the Ifakara Health Institute in Tanzania, "the most basic and undramatic environmental management." It led to a 30 percent drop in A. gambiae's transmission of malaria.

The drawback to this kind of approach is that it must be developed for the conditions that exist in each community, based on the characteristics of their malaria-transmitting mosquitos. By contrast, an intervention like insecticide-treated bednets can be applied almost identically in many different countries - which makes it appealing to donors and international organizations that work in many different countries. Eradicating mosquito habitat can also be very labor-intensive, and require constant vigilance.

Shah also points out that non-chemical methods were used before the world became so enamored with DDT:

These nuanced -- but decidedly low-tech -- programs recall an earlier, pre-chemical era, when malaria control workers made similar gains against the disease by tinkering with the local environment, mostly because they had few other options. In the copper mines of Zambia during the 1930s, for example, malariologists significantly reduced malaria by clearing vegetation, removing obstructions from local waterways, and draining flooded areas. In Panama, during the building of the canal in the early 1900s, anti-malaria workers drained swamps and coated puddles with a thin skin of larvae-suffocating oil, part of a multi-pronged anti-malaria strategy that enabled the canal to be built. Similar measures helped eradicate malaria in the U.S. South.

Environmental management methods fell into disuse after World War II, with the development of a string of synthetic insecticides and drugs, led by DDT and chloroquine. Powerful and highly effective, modern insecticides and anti-malarial drugs can kill malaria mosquitoes and parasites quickly and cheaply, wherever they are used, regardless of local conditions. They can be implemented in even the most remote locales, with minimal infrastructure.

Fashion isn't the only area where things that were once considered old-fashioned suddenly can become the cool new trend.