WEDNESDAY, May 29 (HealthDay News) -- Scientists have discovered
that mutating a smell-related gene in mosquitoes hinders their
ability to sniff out humans from other warm-blooded prey.
Researchers said the findings, published May 27 in the journal
Nature, clearly show how important scent is to mosquito
"hunting preferences." And they hope the results will pave the way
to better weapons against the mosquitoes that transmit diseases
including malaria and dengue fever.
It's well known that certain mosquitoes "specialize in humans,"
said Leslie Vosshall, a professor at Rockefeller University, in New
York City, and senior researcher on the study.
Because they devote their time to moving from one person to the
next, she said, they are the mosquitoes responsible for spreading
diseases such as malaria -- which alone killed close to 700,000
people worldwide in 2010, according to the U.S. Centers for Disease
Control and Prevention (CDC).
Scientists have assumed that odor plays a prime role in how
mosquitoes zero in on people. They are attracted by other factors
-- like body heat and the carbon dioxide people exhale -- but other
warm-blooded creatures also give off those cues.
"None of those factors would be as important as smell," Vosshall said.
And Vosshall's team found clear genetic proof of how important
scent is. In experiments with one strain of disease-carrying
mosquitoes, the researchers were able to "knock out" a gene
involved in odor detection. The result? The bugs lost their ability
to distinguish humans from guinea pigs.
It's not surprising that mosquitoes' odor receptors would be key
in their preference for humans, said Michel Slotman, who studies
disease-transmitting mosquitoes and was not involved with the
But the findings offer important details about the insects'
scent-detecting systems, according to Slotman, an assistant
professor of entomology at Texas A&M University in College
He said the results raise the possibility of using genetic
modification to alter mosquito populations in certain areas where
mosquito-borne diseases are endemic. "The idea behind this approach
is that natural mosquito populations are replaced by ones that have
a gene that modifies their host preference so they no longer prefer
humans," Slotman said.
That's just speculation, however. And Slotman added that, "Of
course, there are possible complications."
One question, he said, is, would mosquitoes with substantially
impaired smell-detection survive in the wild? And even if the
engineered mosquitoes survived, what would be the impact? If people
were still the most abundant and convenient biting target, Slotman
noted, would the "human biting rate" even go down
For their part, Vosshall said she and her colleagues have no
plans "to unleash a race of mutant mosquitoes." Instead, she said
she hopes that a clearer understanding of mosquito genetics and
hunting preferences will aid the development of better insect
It's no use, however, for people to try to mask their scent.
Humans have an odor, Vosshall noted, and they can't change it.
In a second part of the study, her team found that the mutant
mosquitoes were attracted to human skin even when it was protected
by the common insect repellant DEET.
"If you coat the arm with DEET," Vosshall said, "the mutants are still very enthusiastic about human skin. But once they land, they fly away."
That, she said, indicates that the "smell pathway" must be one
important way by which DEET works. But it's not the only way: The
repellant also has some type of action once the insects touch down
on the skin, Vosshall said.
DEET has been widely used as an insect repellant for about 50
years, yet no one is sure exactly how it works, Vosshall noted.
Slotman said that based on this and past research, DEET appears
to have "multiple modes of action."
According to the CDC, malaria alone infected 219 million people
globally in 2010, killing 660,000 -- mostly children in sub-Saharan
A campaign to eradicate malaria worldwide was begun in the
1950s, but it failed -- in part because mosquitoes developed a
resistance to the insecticides used to kill them.
Learn more about
mosquitoes and malariafrom the U.S. Centers for Disease Control
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