Eco-friendly ways to fight malaria take shape in SE Asia

Malaria is transmitted by its vector, the mosquito. Spraying insecticides is a quick, relatively easy and effective way to control the mosquito population and reduce the burden of malaria. The insecticide DDT, for example, was used successfully for mosquito control during the global malaria eradication efforts of the 1950s and 1960s. Today, DDT-resistant mosquitoes can be found in several Southern Asian countries, including India, Sri Lanka and Pakistan. This, together with concerns about its possible negative effects on human health and the wildlife population, has resulted in a reduced usage of DDT in these parts of the world. However, when used in areas with susceptible mosquitoes and by strictly following the WHO guidelines, DDT and other insecticides remain an essential component of malaria vector control today. But they can be complemented with more eco-friendly interventions.

One such technique is based on the fact that some fish eat mosquito larvae. The concept is simple. After mosquito eggs hatch into larvae, it takes another one to two weeks before the larvae turn into adult mosquitoes. During this period underwater, they can be eaten by predatory fish before they have a chance to turn into adult mosquitoes, the carriers of malaria. This approach to malaria vector control is not new but merely forgotten. In fact, it was already used before the discovery of DDT and helped to eradicate malaria in many countries such as Italy, Malaysia and Madagascar.

Interestingly, a very common freshwater aquarium fish is a good candidate for this task: the guppy (Poecilia reticulata). It has a healthy appetite for mosquito larvae. On top of that, its small size, large numbers of offspring, tolerance of variable degrees of water quality and low cost make it ideal for mosquito control. Before releasing the guppies, however, it needs to be determined that they do not disturb the balance of the eco-system. Recently, two Southern Asian countries have given a new life to this old technique and put the guppies to the test.

In Sri Lanka, guppies were released in the river basins below the major dams of the Central Province, a region where malaria outbreaks have occurred. After one year of guppy-treatment, these river basins had significantly reduced numbers of mosquito larvae when compared to untreated basins. The guppies did an even better job than a chemical alternative and were about 2.5 times cheaper to apply.

The story of the southern Indian state of Karnataka, home to a thriving silk industry, is even more remarkable. Here, people were afraid that spraying insecticides to control malaria would not only affect mosquitoes but also their valuable silkworms. Instead, they decided to release guppies and topminnows (also known as "mosquito fish") in village ponds and wells. The results were unlike anything they had imagined. In the Kolar district, located in the southeastern part of Karnataka and home to 36,500 people, malaria went down from 1446 cases in 2001 to only two in 2005. The disease was virtually eliminated. In four other districts, with a combined population of 1.2 million, malaria incidence went down from 73,270 to 497 cases (99.3 per cent). That the project was extended to other parts of Karnataka needs no further explanation.

For those who are still not convinced, using fish has several other advantages: the technique has been successfully applied before and protocols are available; besides malaria, it is also effective against other mosquito-borne diseases in Asia, such as yellow fever and dengue; lastly, it does not harm humans, wildlife and the environment - in contrast to, what many belief, insecticides. Finally, the bigger mosquito-eating fish, such as the tilapia can serve as a food source for the local population.

In our eco-conscious society, now is the time to start thinking about environmentally friendly approaches to mosquito and malaria control. Health officials in malaria endemic regions in other parts of Asia should follow the example of India and Sri Lanka and explore their options for using fish to control malaria.

Frank Konings received a doctorate in microbiology from New York University and worked as a New York State epidemiologist. He has written many scientific articles and opinion pieces about public health issues in Asia, Africa and the United States.