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Don't let the bed bugs bite -

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Norman Swan: Hello and welcome to the Health Report with me, Norman Swan.

Today, do healthy men need to worry about their testosterone levels? And if they don't, why is there such an increase in testosterone prescribing?

Should we all be concerned about our Vitamin B12 levels? Well, maybe if you're getting on, you should.

That's later, after a salutatory message if you're planning your summer holiday in strange hotels or hostels. There are all sorts of beasties to look out for, not the least being the dreaded bedbug, which is the special interest of Dr James Logan of the London School of Hygiene and Tropical Medicine. And what you're about to hear will set your hair on end.

James Logan: Well, we've all heard the story 'sleep tight, don't let the bedbugs bite', and actually when I was young I used to think that they were some mystical creature that lived underneath your bed, but in actual fact they are…

Norman Swan: If only they were!

James Logan: Yes, indeed. They are very, very real. They are much bigger than people think, they are about a centimetre in size.

Norman Swan: A centimetre!

James Logan: Yes. They look sort of like an apple pip, maybe a little bit fatter, especially if they are blood fed. They are real parasites. They do live in and around our beds, and we only have them if we are unlucky.

Norman Swan: Tell me the work you've done on them.

James Logan: We've been looking to develop new ways to help control them, and one of the issues with bedbugs is that they are extremely difficult to find. They will find us very, very easily because they pick up on our smell basically and heat coming from our body.

Norman Swan: So even though they are a centimetre in size when they are fully adult, they are still hard to find?

James Logan: They can be incredibly hard to find, and the reason is that they love to live in any nooks and crannies, hidden away behind skirting boards, underneath your furniture, behind pictures on the wall even or cracks in the wall. When pest controllers come in to investigate a potential bedbug infestation they find it very hard to find them. One way is to use dogs which can be trained to sniff out bedbugs, and they are sniffing out a smell which is associated with the bedbug faeces. And what this smell actually does is it attracts bedbugs, so it's an aggregation pheromone…

Norman Swan: So they are whistling up their mates.

James Logan: It's not for mating, it's just for any other bedbug that's around to basically guide them back to a safe refuge in the crack in the wall. And what we've been doing here at the London School of Hygiene and Tropical Medicine is we've been looking to identify that pheromone, to identify the chemicals that the bedbugs can detect, and in fact we have identified it. We can develop a new trap which could be used to monitor bedbug infestations. So you might imagine, for example, in a hotel you might have 500 bedrooms, and to have an inspector go around every one of those bedrooms would take a very long time. But if you had a sentinel trap in each of those bedrooms that could be checked daily or checked weekly, you would pick up on a bedbug infestation as soon as it started and get rid of the bedbug infestation before it gets out of control.

Norman Swan: Apart from being creepy, do they cause any harm?

James Logan: I'm glad you're talking about the bedbug and not me! Bedbugs can cause a little bit of harm, they are capable of harbouring diseases within their bodies, but there is no evidence that they transmit any disease. In certain countries or even in poor areas in developed countries bedbugs can cause anaemia because they can take so much blood, particularly from children. The other issue is that some people react quite badly to their bites. The worst case scenario is you have an anaphylactic shock, that's quite rare, but your bites can also become infected if you scratch them.

Norman Swan: What do we know about how they are transmitted? I mean, you hear the stories of the backpacker who comes into the hotel room and then you've got it forever, or you are a backpacker and you take it away in your luggage. Is this mythology or true?

James Logan: There's definitely some truth in that. They are the ultimate hitchhiker, they are designed to cling onto fabric, they will do this with ease. They are also being transported in secondhand furniture.

Norman Swan: And you've put volunteers and exposed them to bedbugs to see how rapidly they accumulate.

James Logan: Yes, we have. We did this for a Channel 4 show, we were really interested in finding out how quickly a bedbug infestation could develop just from one or two bugs.

Norman Swan: So how did you do the study, albeit for television?

James Logan: We had a laboratory built in the middle of a field, in the middle of nowhere, and we set up a bedroom in there and we had a volunteer willingly sleep inside that room with the bedbugs and they fed on her blood. She was very brave. It was very interesting because what we also did was we used nightvision cameras which allowed us to see the behaviour of the bedbugs, and that's something we really didn't know anything about. How quickly when the lights went out would they come out of their refuge and find you?

Norman Swan: And?

James Logan: It was pretty immediate, they find their way to the bedpost and climb up the bedpost and straight in there. It was really quite remarkable.

Norman Swan: How many did you seed in the room and then how quickly did they multiply?

James Logan: We put two in the room to begin with, and within just one night both bedbugs came out and fed on the volunteer, then they both laid eggs, and then within about a week those eggs hatched. And so it was quite a frighteningly quick process.

Norman Swan: What can be used to eliminate them? Because it is said that it's almost impossible to get rid of them.

James Logan: It is very difficult to get rid of them. The first job is to find out that they are there, to confirm they're there, and once you've done that one of the most effective ways is to use insecticide. One of the problems with that is that bedbugs have developed resistance to several chemicals, so when that happens we have to find an alternative chemical that has a different method of killing them.

Or what is becoming more fashionable these, days because people don't like to have a lot of chemicals around their household, is to heat a room or even an entire house or apartment up to around 45 to 50 degrees, and this dehydrates the bedbugs very quickly and kills them. And it has proven to be very successful.

The other way you can do it is to bring the temperature right down to below -20, and again that will kill the bedbugs, but again they have their issues as well because bedbugs do hide in any cracks and crevices, and getting the temperature in those areas up to the temperature required can be quite difficult.

Norman Swan: Do they have a natural predator? Can you stick something else in the room like the dog?

James Logan: I'll be honest with you, I have seen a dog eat a bedbug, remarkably, and this was a dog that was sniffing out bedbugs and it did eat it, but apart from any other predators…you know, I'm sure there are things that eat them but I don't think there's anything natural that we can use to control them.

Norman Swan: People do say, you know, just put me in line with a mosquito and the mosquito will bite me and not anybody else, so there's a sense that some people are more susceptible to being bitten than others, and you are looking at this.

James Logan: Yes, that's right, we've been looking at this for some years and actually what we found is, like most insects, mosquitoes have an incredibly good sense of smell and that's how they find us. And so the likelihood is that the reason some people get bitten more than others is due to the way you smell. And we did investigate this by getting a whole lot of volunteers, putting them inside big thermal survival bags, these big silver foil bags, sealing it around their neck and then collecting their body odour which we could then test against mosquitoes.

Norman Swan: So, I've just stopped feeling itchy with the bedbug story and now you're nauseating me! But carry on.

James Logan: Yes, I love my job, it's great. So we collected their body odours, and the only difference that we found between people who get bitten and people who don't get bitten very much is that people who don't get bitten smell differently. And it's not that they lack the attractive chemicals because we all produce carbon dioxide which is an attractant if we are alive. What it was was the people who don't get bitten are producing natural repellents. So it's almost as if your body has a natural defence system against mosquitoes, and we've identified those chemicals and we're now going on to develop a product, a repellent that you can use to actually keep them away.

But even more interesting than that, we've done a few surveys as well on why some people get bitten more than others, and one thing that seemed to stand out was there could be a hereditary component to this, a genetic component to this. So we think that the trait for being unattractive to mosquitoes might actually be passed down from parent to child. And that's something that we are investigating.

Norman Swan: And given that things like malaria have genetically selected some populations, like black populations, for abnormalities of their red blood cells which protect them against the parasite, are those genes for being bitten less more aggregated in African populations, for example?

James Logan: That is a very good question and one that hopefully one day we will answer. We don't know the answer yet. There is a suggestion in some places in Africa that you find that a very small proportion of the population is the more susceptible in terms of contracting malaria, and whether that is due to immunity to malaria itself or due to something like this where they are less attractive to mosquitoes we don't know, but it is an interesting phenomenon.

Norman Swan: And how specific are the commercial repellents on the market to specific bugs?

James Logan: Repellents tend not to be particularly specific to particular insects. They do work better or worse depending on the insect, but generally the best repellent on the market is one which contains DEET, dimethyltoluamide, which is a synthetic chemical, that is the one which works the best. And if you're ever in a tropical region where there is a chance of getting a disease like malaria, that is the chemical that you should use.

Norman Swan: And do we know how it works?

James Logan: We've done quite a bit of research on how DEET works. We used to think that it worked by blocking the sense of smell. So it basically confused the insect and the insect wasn't able to actually detect chemicals that came off our bodies. But more recently what we've shown is that they can actually detect the chemical itself, this is quite weird because DEET is a synthetic chemical, and why would a mosquito pick up on a synthetic chemical? But for whatever reason, we don't quite understand it yet, but it seems like DEET is acting on the receptors that would normally respond to plant chemicals that are repellent to the insect. And so there seems to be this sort of coincidence happening here. We don't quite understand why yet, but it's certainly very interesting. We don't have the full story, but we think that's how it works.

Norman Swan: And you're working across the board trying to get pheromones working against things like mosquitoes.

James Logan: We are trying to get chemicals that we can use to control mosquitoes. What we think is that if we can enhance traps, make them more attractive by having attractants in there, we can have a better surveillance system for mosquitoes that might transmit diseases like malaria or dengue fever, and if we can develop good repellents then we can keep the insects off people and therefore hopefully reduce disease transmission in that way.

Norman Swan: And is there any evidence that traps actually reduce the insect population enough to make a difference, rather than just being for surveillance?

James Logan: That's a very good question. There is not a lot of evidence out there that we can do that. For some populations we can, usually an island population where you don't then get an influx of other insects, but you do need quite a high number of traps. And one of the problems that we have is that no matter how hard we've worked we still haven't been able to develop a trap that is as attractive as a person. And so if you put the best trap in the world next to a person, the mosquito will always go to the person over the trap. So by having repellents in that scenario on the person, you then make the person less attractive and all of a sudden the trap becomes more attractive, and we call that a push-pull control strategy. And so there are studies now going on in Kenya to see whether this strategy will actually work.

Norman Swan: James Logan is a medical entomologist at the London School of Hygiene and Tropical Medicine.

And you're listening to the Health Report here on RN with me, Norman Swan.

Dr James LoganMedical Entomologist
London School of Hygiene and Tropical Medicine

Further Information
Dr James Logan, London School of Hygiene and Tropical Medicine

PresenterDr Norman Swan ProducerBrigitte Seega