Study: Malaria-infected mosquitoes more attracted to human odor

We think of malaria as a disease that infects more than 200 million people a year, with transmission happening through mosquito bites.

But it's not entirely the fault of the mosquitoes. Scientists are exploring how the malaria parasite itself may actually change a mosquito's behavior to make it more attracted to humans, as if controlling its mind so that the bug goes after us.

A new study in the journal PLOS One demonstrates, for the first time, that mosquitoes infected with malaria are more attracted to human odor than uninfected mosquitoes. This is only a proof of concept, however; more research needs to be done to confirm.

“What we've shown is malaria parasites can manipulate the mosquito's behavior to make it sense our body odor much more easily, and that means they’re much more likely to find us," said Dr. James Logan of the Department of Disease Control at the London School of Hygiene & Tropical Medicine, senior author of the study.

Methods

Researchers used 59 malaria-infected mosquitoes and 97 mosquitoes that were not infected. (Only female mosquitoes transmit the parasite.)

A male volunteer wore nylon socks for 20 hours to collect human odor on the material. Scientists then examined how mosquitoes responded to a human-smelling sock compared with a standard nylon sock without a human odor.

Results

Both groups of mosquitoes were generally uninterested in the sock without the human odor. But mosquitoes with malaria paid a lot more attention to the human-smelling sock, landing on it and probing it more than the non-infected mosquitoes.

This represents the first time female mosquitoes have exhibited a behavior change as a result of malaria in response to human odor, the study authors wrote.

Implications

Logan and colleagues have won a research grant to study this further over three years. In the next step, they will take body smell samples from 30 people, "mixing it all up so we’ve got an overall coverage of different types of human odor," he said. Scientists already know that individuals can differ in their attractiveness to mosquitoes.

Eventually, this may lead scientists to identify chemicals that can be used as lures for traps to target malaria-infected mosquitoes. Currently, the traps catch all kinds of mosquitoes, regardless of their malaria status. It would be more efficient, and better for monitoring purposes, to trap only those that have the parasite. This method might even be used to bring the population down.

There are some other intriguing examples in nature of how parasites control the minds of their hosts. A type of fungus, for example, can take over and eventually kill the ants it infects.

But these "zombie ants" don't have the tremendous human impact of malaria-carrying mosquitoes, which caused an estimated 660,000 deaths in 2010.

"The importance is that we showed in a biologically relevant system of a mosquito, a parasite and a blood host, that the parasite can manipulate the behavior of a mosquito," said lead study author Renate Smallegange, who now works at Wageningen Academic Publishers.

More: New discovery may be step toward ending malaria