Its official then! Mosquitoes do like biting some people over others

A mosquito biting
English: A mosquito biting the photographer (Photo credit: Wikipedia)
Are you the target for mosquitoes on a hiking trip? Does your family disagree with you when you say that you are being targeted by these buzzing creatures? Thanks to the paper published by G. Mandela Fernandez-Grandon and colleagues in PLoS One, you now have scientific evidence to tell everybody that you were always right about biting preferences of mosquitoes.  Three questions immediately spring to mind, a when you read something like this. One, how do you prove something as bizarre as this? Second, do scientists really spend time studying something like this? What else do we know about the biting behaviour of mosquitoes? Let’s dwell into them one by one.

How do you prove something like this?

First of all, to prove this you need a bunch of trained mosquitoes at your disposal. Well, mosquitoes are not like chimps who can be trained, so you need a mechanism to let them fly and pick their subjects and then monitor their behaviour. Well, there are Green Fluorescent protein mutant varieties of mosquitoes but the authors of the PLoS study used a simpler option.
Y Tube Olfactometer



                    Image credit: G. Mandela Fernandez Grandon
                    Source: doi:10.1371/journal.pone.0122716.g002
Called, the Y-tube olfactometer, this simple device is designed to allow two stimuli to be placed in the Y shaped arms. The mosquito flies in through the release chamber (at the top) and then actually has an option to choose between the two stimuli being presented to it. The study involved releasing a bunch of 20 mosquitoes in each go and two separate stimuli were placed at the end of the device. The researchers found that when the stimuli were non identical twins, mosquitoes seemed to be prefer one over the other (most mosquitoes were attracted towards one of the twins) whereas in case of identical twins the group of mosquitoes was split in halves, with both individuals attracting almost equal number of mosquitoes. These results were obtained after replicating the experiment 10 times for each set of identical/ non identical twins that were involved in the study.

Mosquitoes prefer biting some people over others

                                                                  Image credit:  www.desciphered.com 

Since identical twins share the same genetic information, researchers now strongly believe that the reason why mosquitoes choose one person over the other might actually lie in our genes. While it is still early to know which genes actually are responsible for this effect, with next-gen sequencing at our disposal, it will not take us very long to pin point the genes in the near future.

Do scientists really study something like this?

Short answer, Yes. 

Long answer, scientists are not looking at this question just because it is intriguing or because somebody has a point to prove.  Understanding the factors that affect mosquito bites will help scientists come up with mechanisms that can be used to deter them. So, hypothetically, if we understand that expression of a particular odour keeps mosquitoes away, then a drug could be designed that will enhance the production of such an odour and can be administered in areas where mosquito bites are causing lethal diseases such as malaria, dengue, chikungunya etc. A long acting drug like this would be much more effective in curbing these diseases than the mosquito repellents that we currently use.

What else do we know about the biting behaviour of mosquitoes?

There is quite a bit that has actually been done in the lab to understand the biting behaviour of mosquitoes. Ansell and colleagues (2002) found that Anopheles gambiae, the major malarial vector in Africa, prefers biting pregnant women over non-pregnant women. Similarly, Lacroix et al 2003 mosquitoes like biting people who have malarial infection rather than those who don’t. People with a greater body mass also act like mosquito magnets was found by Port et al 1980 and later confirmed by Logan et al 2010. More importantly, home remedies like eating garlic or vitamin B does not really have effect on mosquito bite deterrence as was discovered by Rajan and colleagues in 2005 and Ives and colleagues in 2005 respectively. But if you are an alehead, then Lefervre and his team (2010) are sure you are actually inviting Anopheles gambiae to bite you.


If you would like to know more about malaria and how we have responded to it, then there is a nice post about Living with malaria on our blog. Also, Justin Boddey at WEHI, Australia speaks to us about how his team has found a new way to stop the spread of malaria. 

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References:

Fernández-Grandon, G., Gezan, S., Armour, J., Pickett, J., & Logan, J. (2015). Heritability of Attractiveness to Mosquitoes PLOS ONE, 10 (4) DOI: 10.1371/journal.pone.0122716

Ansell J, Hamilton KA, Pinder M, Walraven GE, & Lindsay SW (2002). Short-range attractiveness of pregnant women to Anopheles gambiae mosquitoes. Transactions of the Royal Society of Tropical Medicine and Hygiene, 96 (2), 113-6 PMID: 12055794

Lacroix R, Mukabana WR, Gouagna LC, & Koella JC (2005). Malaria infection increases attractiveness of humans to mosquitoes. PLoS biology, 3 (9) PMID: 16076240

Logan, J., Cook, J., Stanczyk, N., Weeks, E., Welham, S., & Mordue (Luntz), A. (2010). To bite or not to bite! A questionnaire-based survey assessing why some people are bitten more than others by midges BMC Public Health, 10 (1) DOI: 10.1186/1471-2458-10-275

Rajan TV, Hein M, Porte P, & Wikel S (2005). A double-blinded, placebo-controlled trial of garlic as a mosquito repellant: a preliminary study. Medical and veterinary entomology, 19 (1), 84-9 PMID: 15752181

Ives AR, Paskewitz SM, Inter-L&S 101, Biology Interest Groups, & Entomology Class 201 (2005). Testing vitamin B as a home remedy against mosquitoes. Journal of the American Mosquito Control Association, 21 (2), 213-7 PMID: 16033124

Lefèvre, T., Gouagna, L., Dabiré, K., Elguero, E., Fontenille, D., Renaud, F., Costantini, C., & Thomas, F. (2010). Beer Consumption Increases Human Attractiveness to Malaria Mosquitoes PLoS ONE, 5 (3) DOI: 10.1371/journal.pone.0009546


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3 comments:

  1. This is a very interesting article. I would like to add a couple of points which seem to have missed. There is a long standing understanding that mosquito's have an odor preference. The Odor is based on the types of metabolic chemicals secrted in the skin wich are further acted upon by microbial content. Thus it makes sense to implicate skin microbiome as one of the contributors. Currently studies are underway to identify the key microbes. The idea is if you can establish a microbiome that isn't attractive (or even repellant) to mosquito that would solve a lot of the problem. But this approach is years away from practice. There is a second line of thought, which is more challenging. Does plasmodium somehow influence mosquito to have ferocious biting habbits (There are a couple of papers in case of dengue that it is possible, hence not a novel idea). Also does plasmodium infection in humans somehow influence metabolic state such that they are more attractive to mosquito, since that had be an advantage in transmission.

    An important punchline. Easier than designing drugs that people have to take to generate a specific odor, the idea would be to have some sort of sprayable that will change the odor, for at least a lasting time. If this turns out to be the case, it is debatable as to how the mosquito will adapt, since the only way a mosquito will reproduce is they need a blood meal. There is going to be a evolutionary pressure to evolve.

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    Replies
    1. Dear Varun,

      Thank you for visiting our blog and sharing your thoughts with us.

      We do agree with you that we left out the microbiome's role in body odour. There were two reasons for this. One being that microbiomes are a vast topic and it would end up making the post even longer :). The other is exactly what you have mentioned, treatment involving microbiome manipulation is many many years away. We are yet to understand the microbiome and we simply do not know how manipulating it could affect us.

      The second point which you make about Plasmodium parasite being able to influence mosquito biting behaviour has been studied and is detailed in the paper by Lacroix et al 2003 (referenced above). Considering what we know about behaviour modification of organisms, (our post about Mind controlling parasites http://www.coffeetablescience.com/2012/11/mind-controlling-parasites.html), it would
      not be surprising at all, that the parasite is even directing the mosquito to fly to well habited areas and seek out people with lower immunity.

      Reg. your point about designing a repellant rather than a drug, we think other wise. The problem with repellants are that they either get washed off or run out of stock (true for remote areas). So, instead of having to ship bottles of repellant to remote locations and makng sure that everybody uses them, regularly, it would be better, if something like a camp could be organized and these drugs be administered and could last for six months or one year (like a nicotine patch or something) and keep mosquitoes at bay. Wouldn't you agree?

      We would love to hear more from you on this. :)

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    2. Than you editor for clarification. I think that is a reasonably good argument.

      Delete

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