Science Interviews

Interview

Sun, 3rd Jan 2016

Best of NG - Bedbug genetics

Toby Fountain, Sheffield university

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Kat - The first interview Iím featuring is from October 2012, and itís one Iíll never forget. Toby Fountain from the University of Sheffield was responsible for one of the least pleasant experiences Iíd had for a long time, when he took me into the bedbug breeding room in his lab. I asked him to explain the growing bedbug threat, how genetics can help us to understand infestations, and what we can do to prevent picking up these unwanted invaders.

Toby -   Bedbugs were pretty much everywhere until about 1940 and then with the introduction of better public health legislation and powerful insecticides, they were pretty much wiped out across the western world.  Then we found that just after 2000, reports started resurfacing again, and it looks like the bedbugs are now making a bit of a comeback.  But itís become a bit of a mystery.  No one really knows why.  Why now?  Why have they been in obscurity and then suddenly come out?  So, what my research is basically looking at is the potential mechanisms for their resurgence.

Kat -   So, how do bedbugs spread around the place?

Toby -   So, the interesting thing about bedbugs is that they're flightless.  So, they can't move very far under their own steam.  So, what bedbugs actually have the sort of nasty habit of doing is hitchhiking in our belongings.  So, you might go to an infested hotel for example and the bedbug may crawl into your bag or into your clothes.  Itís then very easy for you to jump on a plane or jump on a train, and that bug can be dispersed a huge distance, and thatís how it looks like they're probably spreading.

Kat -   They feed on us, they suck our blood at night when weíre asleep.  Is this a particular health risk?

Toby -   Itís probably more of a mental health problem than a physical [one].  They donít take a huge amounts of blood, but it can give you quite severe reactions.  So, reactions vary from person to person, but you can be bitten multiple times by one bug and might have hundreds of bugs at your property.  I think the real problem is, itís striking you at your home is the thing and there's no real escape from there.  So I think the psychological distress is more of the problem.  And itís also the economic problem for both people trying to get rid of them, but also, itís had a massive cost for the tourist industry.  Obviously, if a hotel is found to have bedbugs, people arenít going to want to go there.

Kat -   And I'm slightly freaking out just sitting here, talking to you.  Itís not very pleasant.  How are you trying to study how these populations have spread around the world recently?

Toby -   So the cool thing that we can do is actually use genetics in order to track their dispersal.  So what we do is basically DNA finger-printing.  So, itís quite hard to finger-print a bedbug, so what we do is we take samples of its DNA and we look at variable regions across its genome.  We can then compare different individuals at these variable regions and we can come up with an idea of how related the individuals are.  So for example, if we find youíve had bedbug infestation at say, a hotel, we can genotype the bugs from there, and then also, genotype a bug that you may have thought youíve brought home.  Then we can match them and see how likely it is that they came from the same place.  So this has a lot of practical applications because it means that in lawsuits and other things like that, we can prove that bugs have likely come from a hotel.  So, it means that people arenít getting wrongfully sued for it.

Kat -   So obviously, a bedbug is very small and humans are very big, and they donít drink a lot of blood.  Why do they need to disperse of they found a nice place where they can live, where there's lots of humans?  Why do they feel this need to travel the world?

Toby -   So, weíve been looking at a few possible answer to that.  So, one thing we looked at, whether inbreeding was playing a role.  So, a lot of animals will actually disperse to move away from their brothers and sisters in order to avoid mating with them.  The other possibility is that itís actually a lack of space.  So, what looks to be the driving factor is actually that bedbugs donít actually live in the bed a lot of the time.  What theyíll do is they'll live in small cracks and crevices surrounding the outside of the bed.  It looks like that these cracks and crevices actually have a certain capacity and once they've reached this capacity, a bug has to move a bit further away. And it looks like as infestations become occupied, that becomes the driving factor, the search for space to hide away.  It's also why it looks like if you go to hotel and you leave your bag near the bed for example, that's the ideal place for a load of new  harbourage space for the bedbugs to crawl into.

Kat -   And tell me a bit about what your research has shown so far, so looking at populations of bedbugs and how they've changed around the world?

Toby -   So genetic diversity is a very important thing to look at because it's how species evolve.  Having diversity is how you can adapt to new situations and conditions.  What we're finding is actually, infestations have very, very low diversity.  It looks like bedbugs are very inbred and while for most species that would be a big problem, it seems to not affect the bugs at all.  They can still rapidly grow.  And it looks like only a few individuals, a very small number of individuals start infestations.  So, what we're seeing is that even one female that's been mated multiple times can come to your house or lay a lot of eggs very quickly, and within a few weeks, you could have a big infestation on your hands.

Kat -   Obviously, when you look at species like humans, inbreeding is really bad and we see inbred human populations, and other animal populations having genetic problems when inbreeding.  So, this doesn't seem to be happening with bedbugs?

Toby -   So, a few mechanisms that this could be.  It could be that, what we see is something called purging.  So what happens is that, you have a load of recessive genes - genes don't occur very often - and that these are lost very quickly.  So every individual that has this gene die.  And so, the genes can't be passed on and are lost from the population.  So once you get this purge, the bugs are actually quite successful because they don't have these deleterious alleles in the population.  So that's one thing we're looking at as well.

Kat -   What should people do if they're concerned about picking up a bedbug infestation?  What should they look out for?

Toby -   So the thing that we really want to emphasise is the importance of being vigilant and just looking out, reducing your chances of picking them when you go to a hotel, and also, looking out for the signs.  So if you think you're being bitten, you want to be looking out for  sort of brown spots around your bed.  When they grow, they shed their skin, so you can also see shed skins around.  You want to look around the cracks, around the mattress, around the obvious places that look like bugs may be hiding.  And if you can catch them early then they're not as hard to get rid of.  And if you're aware, your chances of having a full blown infestation are actually fairly small.

Kat - That was Toby Fountain from the University of Sheffield.

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