Decades of malaria vaccine research has won little ground against a disease that kills over a million people each year. But there's new hope that slowing down the transmission of malaria may be possible, thanks to a novel vaccine for mice that causes their blood to kill mosquitoes that bite them.
Humans are the preferred source of blood for the Anopheles mosquito. When the unwilling blood donor harbors the malaria-causing Plasmodium parasite, the mosquito can transmit the infection to other people. Although researchers continue to work toward a vaccine that fights Plasmodium, they haven't been successful so far. So infectious disease researcher John Beier and vaccine developer Lucy Cardenas-Freytag of Tulane University in New Orleans decided to take a different tack: They wanted to create a vaccine for humans that kills the mosquito after it bites someone who harbors Plasmodium, but before it can transmit the parasite to someone else.
Beier and Cardenas-Freytag, working with molecular biologist and entomologist Brian Foy from Colorado State University in Fort Collins, started by immunizing mice with proteins from genes taken from the midgut of the Anopheles mosquito. They hoped to stimulate antibody production in the mice; transferring these antibodies to the mosquito, they reasoned, would attack the insect and kill it. The team tried to generate an antibody response in three different ways: using two well-known mosquito midgut proteins, PM1 and mucin, and a mix of all known midgut proteins. To the team's surprise, the mucin and mixed immunizations stimulated a white blood cell and mild antibody response in the mice, without harming them. Half of the mosquitoes that then sampled these animals' blood died within 7 days. This suggests that immune cells in blood stay active within the mosquito at least long enough to damage the insect, the team reports in the April issue of Infection and Immunity.
This vaccine approach “sets the stage to attack malaria on a whole new front,” says mosquito biochemist Shirley Luckhart of Virginia Polytechnic Institute in Blacksburg. Such a “killing the messenger” vaccine, focused on the mosquitoes transmitting the infection from one human to another, is “exquisitely suited for the malaria problem,” said parasitologist Thomas Templeton of Cornell University in Ithaca, New York.