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9 November 2009
Dengue Mozzie Breaking the back of break-bone fever - could a tiny bacterium stop the dengue mozzie in its tracks?
TRANSCRIPT: DESLEY BLANCH : The recent outbreak of dengue fever in far north Queensland caused almost 1,000 cases of the disease, the worst outbreak in the last 50 years. It is known as break-bone fever, because of the severe muscle and joint pain that it can cause. Researchers in Queensland are working on a brilliant solution using bacteria to combat the Dengue mozzie and the results have even surprised them. For ABC TV's science and technology program Catalyst, Maryanne Demasi braves a cage full of mozzies to investigate. MARYANNE DEMASI : This is Aedes Aegypti. She carries the virus which causes Dengue Fever. This little mosquito and millions like her are responsible for spreading Australia's worst outbreak of Dengue Fever on record. DR SCOTT RITCHIE : We had rapid transmission, we had situations where by the time we heard about the first person being sick it was already transmitted to other people, even before we killed a single mosquito. DR SCOTT O'NEILL : The temperature was high, we've had large populations of mosquitoes, the outbreak started very early in the wet season, so put all together it's been a particularly good season if you like for dengue transmission. BRIAN MONTGOMERY : This is the latest map that we've got for the work today. MARYANNE DEMASI : The Dengue Action Response Team hit the streets. It was the first time Queensland Health Authorities activated an emergency plan of this magnitude. BRIAN MONTGOMERY : Our core business is to respond to these introductions of Dengue. What's unique about this outbreak is that the number of cases and the rate of new cases has been so high that we've had to actually call on extra help from around the state. MARYANNE DEMASI : An unprecedented number of Dengue Action response teams have been deployed. In Cairns alone, they're spraying up to 300 houses a day. MARYANNE DEMASI : The Dengue mosquito typically lurks close to home. MARYANNE DEMASI : So this is a typical backyard Brian, where would we start looking for mossies? BRIAN MONTGOMERY : Pot plant bases are a great place to start to look. As you can see here waters provided to keep the plant moist, but that also provides water for the Dengue mosquitoes MARYANNE DEMASI : Oh I can see them wriggling. BRIAN MONTGOMERY : Yeah they are. You have got mosquitoes right under your nose ready to hatch out in a couple of days and start biting. DR STEVEN DONOHUE : Doctors will often have trouble deciding whether this is a case of dengue fever or not, particularly in younger people or children who can have a mild illness like the flu but the classical case of Dengue is very typical. Not many diseases will hit you so suddenly with a high fever, severe headaches, terrible aches and pains and such tiredness that you can't move. MARYANNE DEMASI : Each year, Dengue fever affects up to 100 million people and kills more than 20,000 worldwide. There is no vaccination, and no cure. DR STEVEN DONOHUE : The treatment is not specific to this virus. All we can do is give supportive care, pain relief and fluids for those who get dehydrated, or could even go into shock. MARYANNE DEMASI : The virus is usually introduced into Australia from overseas. DR SCOTT RITCHIE : In this case it was a resident who had been to Indonesia, and they infected the dengue mosquitoes. MARYANNE DEMASI : Dengue fever can't be passed directly from one person to another. It can only be spread by a mature female Aedes Aegypti mosquito that has bitten an infected person. The virus then has to incubate inside her for around 2 weeks, and it's only then that she can pass the disease on to her next victim. MARYANNE DEMASI : Queensland researchers saw this time delay as their best chance to beat the Dengue mosquito. They thought that a well known bacteria in fruit flies called Wolbachia could hold the key. DR SCOTT O'NEILL : Some strains of that bacteria are able to shorten the life span of that insect. So we were interested in the idea, could we transfer this life shortening naturally occurring bacteria from fruit flies into mosquitoes where it might shorten the lifespan of a mosquito and prevent it from transmitting Dengue. MARYANNE DEMASI : From the outset, the researchers could see this would be a monumental task. DR SCOTT O'NEILL : We took the bacteria and introduced it into the mosquito tissue culture cells and we grew it in cell culture for 3 years to get it adapted to the mosquito environment. Then we took it from the mosquito tissue culture cells and then injected it into the mosquitoes. MARYANNE DEMASI : It took another 2 years to inject over 10,000 mosquito embryos with the bacteria. DR SCOTT O'NEILL : Once we had it in the embryo, we needed to be able to ensure that it would live and be transmitted from one generation to the next in the mosquito. This bacteria gets passed within the mosquito's eggs from generation to generation. MARYANNE DEMASI : A breeding program was created in the lab to monitor all stages of development from eggs to mosquitoes. DR SCOTT O'NEILL : So this is where we grow the mosquitoes here in the lab. You can see the larval wriggler stage here in the water and down here we have the adult mosquitoes. MARYANNE DEMASI : Oh ok, so what do the mosquitoes actually feed on? DR SCOTT O'NEILL : These mosquitoes and the experiments we do on them, we have to feed them on the blood from human volunteers. MARYANNE DEMASI : And that's all they eat? DR SCOTT O'NEILL : That's all they eat and actually these ones need feeding right now, are you interested in volunteering? MARYANNE DEMASI : Ha, I don't think so, may be you should try? DR SCOTT O'NEILL : Ok I'll show you how to do it then? MARYANNE DEMASI : Dr O'Neill bravely keeps his arm in here for around 15 minutes giving plenty of time for the ladies to feed. Now that's putting your body on the line for science! DR SCOTT O'NEILL : So what we found was that when we transferred the bacteria in the mosquito, it halved the adult lifespan of the mosquito so rather than living to be around 30 days, the mosquitoes were dying around 15 days of age. MARYANNE DEMASI : Which made it almost impossible for the mosquito to spread the disease. This exciting discovery was published in the prestigious journal Science. But while I was here reporting on this research, the scientists revealed two other startling breakthroughs. DR SCOTT O'NEILL : We did experiments where we put dengue virus into mosquitoes containing the Wolbachia infection, the bacteria and we found that the virus couldn't grow at all in the mosquitoes, and this might be more important and more powerful in being able to block dengue transmission. MARYANNE DEMASI : If the Aedes Aegypti mosquito can't propagate the disease, that would stop the spread of Dengue dead in its tracks. DR SCOTT O'NEILL : The other thing that we've found is when the bacteria is present in the eggs, the eggs can't last as long in a dormant state. And so potentially they will not be able to survive the dry season. And so this should see a great reduction in the numbers of mosquitoes as well that are available to start the population off in the following wet season. MARYANNE DEMASI : Making their idea work on a large scale is the tricky bit. A purpose built facility at James Cook University houses thousands of mosquitoes. MARYANNE DEMASI : Wow, this is like a real back yard. DR SCOTT RITCHIE : Well that's exactly what it's supposed to be. It's a simulated backyard of a Queenslander house, like you might find in Cairns and where you might get dengue. MARYANNE DEMASI : I see the mossies. DR SCOTT RITCHIE : There are about 5000 of them, half infected with Walbachia and the other half just normal wild Dengue mosquitoes, none of them infected with Dengue, by the way. MARYANNE DEMASI : That's reassuring to know, what's down there? DR SCOTT RITCHIE : What we've got here is a perfect mosquito habitat. Dark, shady, high humidity, you've even got dirty towels. MARYANNE DEMASI : I see the dirty towels and shirts. DR SCOTT RITCHIE : Yeah, yeah. MARYANNE DEMASI : The researchers are hoping this controlled environment will tell them whether their plan to overtake the Dengue mosquitoes with the bacteria-infected mosquitoes will work out in the field. DR SCOTT RITCHIE : Well one of one of the issues is, how do you go about releasing them? Do you release a bunch of mosquito larvae, do you release adult mosquitoes, how many do you release per house, how many do you release per block? Those are ... the devil's in the detail and we've got to nut some of those issues out. So it's not going to happen overnight. MARYANNE DEMASI : If the trial is successful they hope to deploy this new dengue control measure throughout Australia's tropics, as well as in Thailand and Vietnam. DR SCOTT O'NEILL : We're very excited about these results. We think it has the potential to eliminate dengue transmission completely. DESLEY BLANCH : Doctor Scott O'Neill is one of the Queensland researchers who is building a scientific defence against Dengue Fever; Maryanne Demasi with that report. Back |
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