How a fungus may help control malaria

The World Health Organization’s World Malaria Report 2010 highlights a massive effort to control malaria. For example, insecticide-treated mosquito nets have been provided to protect more than 578 million people in sub-Saharan Africa and 75 million people are now protected by indoor residual spraying.

However, deaths from malaria worldwide in 2009 still totalled 781,000 and the disease shows a resurgence in some areas, such as Rwanda and Zambia. Much work is still to be done to achieve the goal of ending malaria deaths by 2015, as suggested by the UN Secretary-General’s special envoy for malaria Ray Chambers.

A major problem is finding a way of eliminating mosquito larvae without environmental damage. Mosquitos breed in open water, where the larvae feed on fungi and other micro-organisms on the water surface before pupating and hatching into adults.

Some biological methods have been tried, such as encouraging dragonflies, the larvae of which eat mosquito larvae, and toads, which eat adult mosquitos while their tadpoles also feed on the larvae. Mosquito fish, Gambusia affinis and G holbrooki, are voracious predators of mosquito larvae but unfortunately also eat other fish and those useful dragonfly larvae.

Researchers from Wageningen University in the Netherlands, are studying two fungi, Metarhizium anisopliae (formerly called Entomophthora anisopliae) and Beauveria bassiana. Both are also used to control beetles, thrips and weevils.

The fungal spores enter the mosquito larvae then germinate to produce hypae which spread through the body consuming its internal contents thus killing the larvae before they pupate. More spores are then released to continue the process.

At a test site in Kenya the researchers used a synthetic oil as a means of spreading and retaining the fungal spores on the water surface. This formulation proved to be 50 per cent more effective than using the spores alone and reduced pupation levels to less than 20 per cent while appearing to pose minimal risk to other aquatic organisms.