Using Mosquitoes To Put The Bite On Malaria

April 25, 2011

Joanne Silberner

abadonian
Bite me: Could malaria-infected mosquitoes protect against the disease?

The parasite responsible for the intense fevers, chills, and headaches of malaria has proven elusive to the scientific effort to come up with a vaccine.

So Dutch researchers are trying a new approach — "vaccinating" people by having them get bitten by mosquitoes carrying the malaria parasite, similar to how people get infected in the real world. Their way is different than the conventional vaccine approach of injecting people with bits and pieces of the malaria parasite, or a parasite that's been weakened in the lab.

Those approaches aren't working all that well in clinical trials so far. The Plasmodium parasite is a notoriously tough challenge for vaccines because it spends most of its time hiding inside red blood cells and liver cells, out of sight of the immune system – one reason why it was able to kill 781,000 people in 2009. Most of those were children in developing countries.

In the Dutch experiment, 10 volunteers were bitten multiple times by malarious mosquitoes. The researchers then gave the volunteers an anti-malaria drug, chloroquine. (And yes, the researchers were very careful to pick a malaria type that responds to chloroquine, not a chloroquine-resistant variety.)

A couple of years ago, the researchers reported that this process works in the short run to protect against malaria. But that's not such a big deal. People naturally infected by malaria build up an immunity that holds for several months.

What's new is that the researchers went back to six of the volunteers 28 months later. Once again the volunteers allowed themselves to be bitten by malarious mosquitoes. Four of the six did not get infected. And the immune systems of the remaining two put up a fight – their infections were delayed (and quickly treated). The results were published online in The Lancet.

Wondering who would volunteer to be bitten by a malarious mosquito? Study author Robert Sauerwein of Radboud University in the Netherlands says most were university students. And the trial was designed pretty carefully.

A lot more work needs to be done to test this approach. This study was very small – only six people. And the researchers note that they may have stacked the deck a little – they used the exact same strain of malaria to infect, and to re-infect. And they worked with adults with mature immune systems, rather than children.

It's not clear yet why the experimental vaccination protected longer than infection by mosquito in the field. The anti-malarial drug could have helped. Or maybe it was the intense exposure to multiple bites at the same time. Whatever the reason, they say, it's worth investigating given how well the malaria parasite has been at outsmarting attempts to get rid of it.

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