Eau de Manipulation: Malarial Mosquitoes More Attracted To Human Scent

By Christie Wilcox | May 15, 2013 4:00 pm

An Anopheles gambiae mosquito gorging herself on blood. Photo by Jim Gathany, from the CDC’s Public Health Image Library

By the time you realize what has happened, it’s too late. An Anopheles gambiae mosquito can land on your skin completely unnoticed. While you continue unaware, she stealthily walks over your exposed flesh, searching, probing the surface of your skin with her proboscis until she finds a blood vessel. She then situates her body perfectly at just the right angle, hunches down, and plunges her needle-like mouthparts into your skin. Tiny pumps pull the warm, protein-rich blood into her mouth.

With every millisecond increasing her chances of exposure, she drinks as quickly as she can. Your hand isn’t the only obstacle she faces: even as she sucks, your body senses the wound and attempts to plug the hole by forming a clot. She needs your warm, nutritious blood for her eggs, so she’s not about to let your protective mechanisms interfere. To ensure her meal keeps flowing, she pumps saliva laden with anti-coagulants and vasodilators  into the wound — and that’s when it happens. That’s when the Plasmodium falciprum sporozoites that have been waiting patiently in her salivary glands enter your bloodstream. Dozens can hitch a ride in her saliva, but it only takes one to cause malaria. One single, microscopic protozoan is enough to kill you.

Responsible for the most dangerous kind of malaria and at least half of malaria cases worldwide, Plasmodium falciprum is estimated to kill somewhere between 500,000 and 1 million people every year. In recent years, the parasite has developed resistance to many of our best treatments, leaving doctors without options in the over one hundred countries where malaria is endemic. While scientists continue to research new means of treatment from vaccines to drugs, nations struggling with malaria have shifted focus to prevention. Recently, this means scientists have become particularly interested in mosquito behavior to develop better, cost-effective control mechanisms. But a new study in PLoS ONE today suggests we know less than we might have thought, and that the parasite may be influencing its host mosquitos in ways we never even imagined.

“So far, most studies of Anopheles gambiae mosquito behavior have been conducted with uninfected mosquitoes,” write the authors, “but our data demonstrate that such results may not be representative of infected mosquitoes.” Previous studies found that Plasmodium-infected mosquitos probe skin more, bite more often and ingest larger meals than uninfected ones, but the scientific team comprised of scientists from the Netherlands, United Kingdom, and United States wondered whether infected mosquitos behave differently before they land.

Many parasites with multiple hosts are known to alter one hosts’ behavior to increase transmission to the next. Toxoplasma gondii, for example, suppresses rats’ fear of cats by altering how they respond to feline smells. The research team wondered if Plasmodium could control mosquitos along the same lines, so they tested how uninfected and infected mosquitos reacted to the scent of human skin. Their results were staggeringly significant.

Figure 1 A from Smallegange et al. The total number of landings by uninfected (green bars) and P. falciparum infected (red bars) mosquitos in response to no odor (left) or human skin odor (right).

Infected Anopheles mosquitos landed on the human-scented surface more than three times as often as non-infected mosquitos. “These results suggest that malaria-infectious females are more attracted to human odors than uninfected mosquitoes,” write the authors. “This is the first indication of a change in [mosquito] behavior in response to human odor, caused by infection with P. falciparum.”

The authors hope this research spurs further study into the ways in which Plasmodium alters mosquito senses. New types of attractant smells, for example, could lead to breakthroughs in trapping technology and provide powerful allies in the struggle against malaria.

But the discovery that mosquitos act differently when infected has its downsides, too. If the parasites can change how the mosquitos smell, how much does this alter how they behave? Are the usual battery of deterrent or attractant smells less effective? Is the alluring scent enough to draw mosquitos to feed when they normally wouldn’t, making our nightly netting less meaningful? Are there any other ways that the parasite alters its host, and what do these changes in behavior mean when it comes to bite prevention?

There is a long road ahead before scientists will fully understand the complex interactions between Plasmodium and their hosts. Studies like this one reveal just how little we understand these deadly parasites of ours, and how much more we have to learn if we want to win the battle against them.

Citation: Smallegange R., van Gemert G.J., van de Vegte-Bolmer M., Gezan S., Takken W. et al. (2013). Malaria Infected Mosquitoes Express Enhanced Attraction to Human Odor. , PLoS ONE, 8 (5) e63602. DOI:

CATEGORIZED UNDER: Evolution, Health, select, Top Posts
  • smartypants

    itv is sooooooooooooo long!!

    • Blade Avuari

      I personally disagree. Although this article is a bit longer than some of the others, I have been searching for articles that explain alot. But, I do understand your opinion.

  • brian

    I have often wondered about the Toxoplasma Gondii organism and if it had some ability to hyperpotentiate the hormone oxytocin in mammals (lessening fear or inhibition).

    Oxytocin derivatives have also been found in mosquitoes and this may be the method by which the malaria organism also plies its work in mosquitoes.

  • http://www.facebook.com/misterkleen John Raguso

    No mention here of the possible connection between Thalassemia and immunity to Malaria.. I’ve been diagnosed with Thalassemia and I’d like to know if I smell atrocious to ‘skeeters or not

  • http://www.facebook.com/Vatossan Cesar Elcesar

    i hate mosquitos so much. when i catch one i take one limb at a time, and if i can i’ll burn it.

NEW ON DISCOVER
OPEN
CITIZEN SCIENCE
ADVERTISEMENT

Discover's Newsletter

Sign up to get the latest science news delivered weekly right to your inbox!

Science Sushi

Real Science. Served Raw.

About Christie Wilcox

Christie Wilcox is a science writer and PhD Student at the University of Hawaii, where she studies the protein toxins in venomous fish. She is renowned in the science blogosphere for her delicate balance of contemporary science and scientific perspective seasoned with just the right amount of wit. Her award-winning posts have been featured in The Open Laboratory: The Best Science Writing On Blogs four years running and landed on the pages of major media outlets including The New York Times and Scientific American. To learn more about her life and work, check out her webpage or follow her on Twitter, Google+, or Facebook.

ADVERTISEMENT

See More

ADVERTISEMENT

@NerdyChristie on Twitter

Collapse bottom bar
+

Login to your Account

X
E-mail address:
Password:
Remember me
Forgot your password?
No problem. Click here to have it e-mailed to you.

Not Registered Yet?

Register now for FREE. Registration only takes a few minutes to complete. Register now »