Malaria and foot odor-the missing link!

Via Gawker.com and the LA Times, here’s a news alert that all college students should be mindful of. Researchers at the London School of Hygiene and Tropical Medicine have published in the medical journal PLOS One a new defense against malaria transmission. Malaria is a disease which affects a large proportion of the world’s population, with an estimated 220 million cases (nearly 1 in 20 people) worldwide in 2010. It is caused by the several species of the protozoan genus Plasmodium, and transmission requires specific species of mosquitoes that are essential for the life cycle of Plasmodium. There are treatments for malaria that can help infected patients to clear the parasite, but there is currently no vaccine. Main methods for control for the transmission of malaria have traditionally focused on controlling the reproduction of mosquitoes.

The experiments conducted by the researchers were simple; new adult female mosquitoes were fed human blood which was either infected or uninfected with Plasmodium. Following verification of infection, mosquitoes were introduced to socks (20 Den panty sock, HEMA, The Netherlands) that had been worn for 20 hours beforehand

…by a male volunteer of whom the relative attractiveness to An. gambiae s.s. compared to 47 other men is known…

Control socks, of course, were fresh right out of the package. The researchers constructed a mesh matrix, and measured the rate at which the mosquitoes landed on the matrix (landing rate).

journal.pone.0063602.g001

As can be clearly noted from their data figure, infected mosquitoes were 4 times as likely to be attracted to the human odor than uninfected mosquitoes. The authors conclude that the presence of Plasmodium is altering the behavior of the mosquitoes, which may increase the rate of transmission as the population of infected vectors (the mosquitoes) rises. They suggest that current mathematical models for malaria transmission may be underestimating the rate at which the protozoan spreads through populations, as generally uninfected mosquitoes are used in behavioral studies and do not take into account the effects of the parasites themselves on vector-host interactions. Effective malaria control programs need to accurately model all aspects of parasite/vector/host interactions.

From the point of view of the pathogen (Plasmodium,) this is a perfect strategy. Plasmodium species depend upon the mosquito vector for the sexual portion of their life cycle, and this requires approximately 2 to 3 weeks to occur. As this occurs, it is advantageous for the organism not to be transmitted to a new host during a blood meal. However, after sexual maturation has occurred and the new sporozoites migrate to the salivary glands of the mosquito, modification of behavior will allow the subsequent transmission back into a new host during as the mosquito feeds. Long time fans of BIO230 will recall how another Apicomplexan protozoan, Toxoplasma gondii, has been found to potentially modify its host’s behavior, leading to the inappropriately named “Crazy Cat Lady Syndrome.”

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About ycpmicro

My name is David Singleton, and I am an Associate Professor of Microbiology at York College of Pennsylvania. My main course is BIO230, a course taken by allied-health students at YCP. Views on this site are my own.

Posted on May 16, 2013, in Braaaains!, Strange but True. Bookmark the permalink. 2 Comments.

  1. I wonder if a similar host-parasite relationship exists between mosquitoes and West Nile Virus. Would infected mosquitos be “hungrier” than non-infected? A similar experiment wouldn’t be hard to replicate…if only we had the proper biohazard level at YCP. I even know a few good sock candidates.

    • I was skeptical about the possibility that WNV might alter mosquito behavior, due to the very basic difference in symbiotic relationship between mosquitoes and Plasmodium and WNV. With Plasmodium, the pathogen carries out part of its reproductive life cycle in the insect vector, and without that specific host, the sexual cycle cannot occur. With West Nile Virus, the pathogen is being carried along with a blood meal, but no portion of the viral life cycle occurs within the insect. This relationship is much more of a “mechanical” vector relationship, and the only real specificity is that mosquitoes have a strong (but not absolute) preference for the animal from which they get a blood meal. This posting from BIO230 pointed out that reptiles can act as reservoirs for WNV in North America.
      However, a quick Google search for “viruses that modify behavior” turned up this primary literature citation from Pubmed, describing the relationship between Barley Yellow Dwarf virus, a virus that infects wheat, and its insect vector the aphid. This citation proposes the Vector Manipulation Hypothesis. The authors suggest that vector and host modifications further complicate the web of interactions between all of the players in the spread of an infectious disease.
      Note to any interested Senior Thesis students: the Biosafety concerns voiced by Heather G. regarding WNV will be a non-concern with BYDV. The only people who will be annoyed with that choice of pathogen will be Kleiner and Smith.

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