The experimenters wore nylon socks to collect their foot odor (a clean nylon sock was used for a control). Then for a period of three minutes they counted how many mosquitoes preferred to land below the (stinky) nylon sock instead of the clean one. It wouldn't seem surprising to me that the mosquitoes preferred to land by the smelly nylon sock - after all that sock smelled like food. What is interesting is that mosquitoes landed by the smelly nylon sock much more often after they were infected with malaria. The implications are obvious - malaria infected mosquitoes are more attracted to us than mosquitoes that aren't infected.
|Figure 1 in the mentioned article. Notice that infected mosquitoes land significantly more often than uninfected mosquitoes|
Specifically, these researchers were looking at the Anopheles gambiae. Past research (which is cited incorrectly in the article) has already shown that An. gambiae infected with malaria eat more frequently and for a longer time than those not infected. This study is another evidence that the malaria parasite is able to control the actions of it's host. The researchers point out the advantages of this mechanism - if an infected mosquito is attracted to a host the parasite can be transmitted more effectively.
This isn't the first example of so-called "mind controlling" parasites. Dicrocoelium dendriticum is a parasite that affects the behavior of ants. Ants infected with Dicrocoelium dendriticum will climb to the top of a blade of grass and wait in the hot sun to be eaten by grazing cattle - the next step in the parasite's life cycle. This current study does not prove that malaria has this extent of mind control over the mosquitoes, but it is interesting that infection with malaria changes a mosquito's behavior in the favor of the parasite. The authors mention that more research is required, specifically they are now investigating the behavior as a function of the parasite's life cycle (will a mosquito be more attracted to human odor after the parasite reaches it's transmissible stage?) Current studies of malaria transmission often use uninfected mosquitoes or computer models based on behavior of uninfected mosquitoes, which may be inadequate, given this new research.
Renate C. Smallegange, Geert-Jan van Gemert, Marga van de Vegte-Bolmer, Salvador Gezan, Willem Takken, Robert W. Sauerwein, & James G. Logan (2013). Malaria Infected Mosquitoes Express Enhanced Attraction to Human Odor PLOS ONE DOI: http://dx.plos.org/10.1371/journal.pone.0063602