Skip to 0 minutes and 10 seconds So what these mosquitoes have done, what’s made them so incredibly successful, is that they have adopted the
Skip to 0 minutes and 18 seconds human, throwaway environment: the human jungle in which we provide all kinds of the containers for them to lay their eggs in. They can be very small containers, even a Coca-Cola can for example, generally not much bigger than a barrel of rainwater perhaps. And if we look at the - at the infested containers very very often we find that most of them are quite small and indeed the mosquitoes are remarkably adapted to laying in these small containers of water. The females don’t lay many eggs, shall we say, in the same basket. In other words they distribute their eggs among many small sites, and in that way they are able to exploit all the breeding sites that we provide for them.
Skip to 1 minute and 7 seconds The differences that are most important are, above all,
Skip to 1 minute and 11 seconds the difference in feeding habits: Aedes albopictus will just about feed on
Skip to 1 minute and 16 seconds anything: on birds, on humans and even on amphibians and reptiles. Aedes aegypti on the other hand is strictly anthropophilic. It really only likes to bite on people. In some studies that we did in the Caribbean we found that only 3% of blood fed mosquitoes - aegypti -
Skip to 1 minute and 38 seconds were actually not human blood, they were in fact cats. As far as transmission dynamics are concerned it’s obviously a lot better for a virus if every time the mosquito bites it bites a primate, because the viruses we’re talking about are primate viruses, whereas with albopictus, biting on different creatures that are not susceptible to the virus, quite clearly it’s not such an effective vector. If you’d asked me, let’s say 20 or 30 years ago, what is the distribution of Aedes albopictus, I would have said it’s an Asian species. Now, if you asked me the same question, I’d tell you it’s all over the world. How did it do that so quickly? Well, we spread it around the world.
Skip to 2 minutes and 32 seconds A quick personal story.
Skip to 2 minutes and 34 seconds I worked for a time in Memphis, Tennessee: Elvis Presley’s city. I was working on the St Louis encephalitis, a virus that is closely related to dengue and yellow fever. One day in my collections, something turned up that I
Skip to 2 minutes and 50 seconds never expected: Aedes albopictus. Memphis is pretty well in the middle of nowhere it’s certainly well inland, and when I tried to think of the ways that it might have come in, there didn’t seem to be anything very obvious. Two years later we got a call from Houston, Texas, where it turned out the mosquito was absolutely rampant. When I went down there and I found it was breeding particularly prolifically in discarded used tyres. I was doing what entomologists do, looking at the mosquitoes in these tyres, when a pickup truck went past me and stopped further down the road and two guys got out and they started sifting through tyres and occasionally chucking one into their pick up.
Skip to 3 minutes and 45 seconds I went to ask them what they were doing and they said “well, our company ships these tyres to Guatemala and Mexico”. Of course I was rather shocked because those were countries with endemic dengue. So I said to them “well, how does your company get enough tyres to be able to export them to those countries?” and they said “ah well, we import them. “ It turned out it was actually they were being imported from Japan. And I became the world’s leading used tyre epidemiologist! What I found was that the Japanese were exporting huge numbers of tyres, millions of tyres, to about 150 countries in the world. The United States was not far behind. And many European countries were also involved.
Skip to 4 minutes and 37 seconds All kinds of reasons why people were shipping tyres, and many of them to be retreaded. And many others for other applications. When we went, when I’m talking about’we’I’m talking about the Centers for Disease Control, we went up to Seattle and we inspected 20,000 tyres and we found five species of Japanese mosquito, and it was quite clear that there was no way of stopping this importation so Aedes albopictus now is rampant in many parts of the east and southern United States, as far north as - close to New York. It is now present in at least 20/25 countries in Europe and the Middle East.
Skip to 5 minutes and 31 seconds And it is present in some African countries, at least 5 of them, and has been implicated in yellow fever and chikungunya transmission so this is a very successful mosquito. What bout Zika? Well, what about Zika? We don’t know a lot about Zika. We know that it’s another of those African viruses. We know that it is transmitted by aegypti and we know that it’s capable of infecting Aedes albopictus as well. We’ve never paid much attention to it because it didn’t seem to be very serious and of course we now know it is serious. How far north in Europe is it likely to go?
Skip to 6 minutes and 15 seconds Well, transmission by a mosquito is very, very much more complicated complex than just a matter of, say, temperature. A lot of ducks have to be in line before transmission occurs. We don’t know an awful lot, as I say, about Zika. So it’s very hard to say, “you know, if albopictus gets as far as Stockholm we’re going to have to Zika as far as Stockholm”. We can say that it’s not probable that we’re going to have transmission of the virus through the winter, so any transmission will depend on introduction in a traveller. There could be massive epidemics. In many ways we assume that transmission may be rather similar to dengue.
Skip to 7 minutes and 3 seconds Dengue in Europe has a long history, we don’t know why, really why, it disappeared, but we know for example in the 1920s, there was a massive epidemic in Greek refugee camps in which probably a million people were infected and there were thousands of deaths. Now of course refugee camps is another issue very much in mind at the moment. Let us see what happens in terms in terms of outbreaks.
The success of Aedes
Over the next few steps we will look at the spread of Aedes aegypti and Aedes albopictus across the world, but what are the reasons for this species’ success?
In this step Paul Reiter, Professor of Medical Entomology at the Institut Pasteur, tells us more about how the distribution of Aedes has changed and why, highlighting our influence on its expansion with a personal story and the potential implications for spread of the Zika virus.
Paul highlights one particular example of how Aedes has been able to spread from one continent to another. Do you think there is anything we could have done to stop this or was the spread inevitable?
Please note that the audio for this step was captured remotely and its quality will not be of the same standard as a studio recording. If you experience problems with the audio please use the subtitles or transcript file.
© London School of Hygiene & Tropical Medicine