After humans, mosquitoes are the most dangerous animals on the planet. For much of the world, a mosquito bite can mean serious illness or death from malaria, yellow fever, chikungunya, Zika and dengue.
The solution has been — well, we haven’t had a good solution. Insecticide-treated bed nets and pesticides applied inside homes protect against the malaria-carrying anopheles mosquito, which bites at night. But Aedes aegypti bites during the day. That’s the mosquito that carries Zika and dengue, which infects 400 million people per year. No usable vaccine exists for either disease.
So we spray large areas with pesticides, which affects the whole ecosystem; it’s an ax, when we need a scalpel. And any pesticide eventually becomes useless when mosquitoes evolve to resist it.
But now there’s a new response: We can create good mosquitoes — those infected with bacteria that block or greatly reduce transmission of disease — and use them to vanquish the bad ones.
Townsville, Australia, is a beautiful city of 193,000 people, on the Great Barrier Reef in Australia’s tropical northeast. While dengue is not endemic, it had been possible to catch it in Townsville when travelers from other countries imported the virus to Townsville, where local Aedes aegypti mosquitoes then spread it to others.
But in 2014, the World Mosquito Program at Monash University in Melbourne began releasing good mosquitoes in Townsville. Between 2014 and 2016, releases grew to cover practically the whole city. To reassure a public hesitant about signing up to live with even more mosquitoes, the program held meetings and events to explain the project and ask households to participate. Thousands of households got their own Mozzie Box, a special bucket with eggs and mosquito food, to raise and release the good mosquitoes. And elementary schoolchildren got Mozzie Boxes — with a magnifying glass and a booklet — as part of a citywide science project.
Imported cases of dengue kept rising in Townsville during the mosquito releases. But local transmission of dengue virtually stopped. Four people caught dengue without having traveled abroad, compared with 54 in the equivalent period before the program. And only one of the four lived in an area where good mosquitoes had taken over; that person had been highly mobile, and so could well have become infected in a different neighborhood.
What’s a good mosquito? It’s one infected with bacteria called Wolbachia. It’s harmless to humans and vertebrates, and occurs naturally in most insect species.
Wolbachia does not occur naturally in Aedes aegypti. Scientists had tried to inject it into the mosquito’s eggs, but had no luck until 2005, when Zhiyong Xi, then a doctoral student at the University of Kentucky, found the way. It wasn’t genetic modification. The key was that these mosquitoes, when born from infected eggs, are infected themselves — including their own eggs. In that way, the infection continues.
A Wolbachia-infected female will pass the infection to her offspring whether or not her mate is infected. An uninfected female, however, can’t have offspring with an infected male; those eggs will not hatch. And females only mate once. This gives Wolbachia-infected mosquitoes a transmission advantage.
Researchers in a variety of locales enduring tropical diseases are testing several ways to employ Wolbachia. The World Mosquito Program aims to replace the local mosquito population with a Wolbachia-infected population, the infected mosquitoes forming a larger and larger proportion of the total with each generation.
The program releases both male and female Wolbachia-infected mosquitoes. It places traps to catch mosquitoes, and stops releases when the percentage of mosquitoes found to be infected reaches a critical point. In Townsville, that was 50 percent for two consecutive weeks.
The infected mosquitoes’ transmission advantage was enough to tip the population. In most mosquito-release areas in Townsville, all or nearly all mosquitoes are now Wolbachia- infected, and that has remained stable. (In a few neighborhoods, however, Wolbachia’s control has fluctuated and the program has had to release additional mosquitoes.)
It’s great for public health that a single treatment campaign provides lasting effects. That will help governments do it cheaply. And the job will have to be done by governments, because there’s little profit in it, said Professor Scott O’Neill, who was dean of science at Monash University in Melbourne and now directs the mosquito program. “We have no business model.”
The program is working with governments to run field tests in 12 countries, including Australia, Vietnam, Indonesia, Brazil, Colombia and Sri Lanka. In Rio de Janeiro, the project covers 1.2 million people, and in Medellín, it covers 2 million: in both, scaling up was quick in response to Zika. In several places, the program is working on national coverage. So far, results have been reported only from Australia and Yogyakarta, Indonesia. But those have been excellent.
Dr. O’Neill said that he and his colleagues had worried about communities’ reaction to the program. “But people who understand dengue and live in transmission areas are horrified and scared,” he said. “I live in Saigon, where transmission is through the roof. We’re not seeing any community pushback.”
The cost of the program in Townsville was per person covered, but that was because it’s a sprawling city. In a place like Rio, where people live closer together, the cost is per person. That might save Rio money over all. It’s a onetime cost. And treating dengue and Zika are expensive; babies with Zika-related microcephaly may need lifelong care. Dr. O’Neill said he hoped to get the cost down to per person.
The program’s strategy of replacing bad mosquitoes with good ones has some disadvantages as well. Unfortunately, it doesn’t reduce the number of mosquitoes or their bites.
Also, there’s a trade-off. The better Wolbachia does at blocking disease, the more it weakens the mosquito. Weaker mosquitoes are less able to spread into the population and maintain their hold. The World Mosquito Program is using the best Wolbachia strain possible, said Dr. Xi, who is not involved in the program. “But the technology needs to be improved so we are able to develop a mosquito that can completely block the virus and still be able to spread into the population.”
Dr. Xi, who is now a professor at Michigan State University, uses Wolbachia in a different way: to eliminate the mosquito population. He heads a research collaboration between M.S.U. and Sun Yat-sen University, in which the universities built a mosquito factory in Guangzhou, China. Dr. Xi also is leading a project with Autonomous University of Yucatán to start another factory, in Merida, Mexico.
The China factory can produce 60 million Wolbachia-infected male mosquitoes per week, he said. Unlike the replacement strategy, an elimination strategy releases only males. Sex-sorting is expensive and difficult. Essentially, mosquitoes are put through a giant sieve, which separates males from the larger females. But releasing only males makes it possible to clear an area of all mosquitoes: When the existing females, which are all uninfected, mate with an infected male, their eggs won’t hatch. So the population is gradually reduced.
This strategy creates a double attack on dengue and Zika: The infected mosquitoes don’t transmit disease, and their population dwindles to the point where they can’t keep an epidemic going. It could also get a warmer welcome from local residents, as the only mosquitoes released are males, which don’t bite.
It has some disadvantages. Sex-sorting is not only costly, it’s imperfect — and letting even a few females through can be fatal to the project. More important, the gains don’t last. Mosquitoes will fly in from untreated areas and re-establish a colony, so the project must start anew every year.
“If you have to release mosquitoes every year to keep the numbers down, it becomes a business,” said Dr. Andrea Gloria-Soria, an evolutionary biologist who is an agricultural research scientist at the Connecticut Agricultural Experiment Station. “Which is what I don’t like. These problems are mostly third-world country problems, and there’s no money there.”
In Guangzhou, Dr. Xi is working with local officials to test a combination strategy. For the last three years, mosquitoes have been infected with Wolbachia and then zapped with low-dose radiation, which sterilizes the females. He said that the mosquito population has dropped by 90 percent on average, and some areas have completely eliminated mosquitoes.
Most Americans don’t worry about dengue and Zika — yet — but would love to see fewer mosquitoes. Dr. Stephen Dobson, a professor of entomology at the University of Kentucky, founded MosquitoMate, a for-profit company that works with mosquito-abatement programs in the United States. MosquitoMate’s largest projects are in Fresno, Calif., and Miami, with more than 150 acres treated in each city. One unexpected partner in Fresno is Verily, the life-sciences division of Google’s parent company, Alphabet. Verily is trying to use machines and algorithms to raise, sort, release and monitor Wolbachia mosquitoes.
Dr. Dobson said that mosquito populations drop by 70 to 95 percent — the larger the area, the stronger the effect. But it’s expensive. He sells the service to individual homeowners in Lexington, Ky., who will pay ,500 for weekly mosquito releases this summer.
Any time we play God with nature, we need to worry about the consequences. But Wolbachia is natural — most insect species already carry it. And any possible environmental impact is far less than what we create by spraying. No scientist I talked to worried that Wolbachia could help mosquitoes transmit new diseases such as H.I.V. — which, let us give thanks, is not mosquito-borne. Mosquitoes are very particular about which viruses they can transport. “Mosquitoes aren’t flying syringes,” Dr. Dobson said.
What’s much more likely is that the benefits of Wolbachia won’t last. At some point, pathogens are all but certain to evolve to resist Wolbachia, just as they evolve to resist insecticides. Dr. Gloria-Soria said that the elimination strategy might be better able to stave off resistance, because it must start over each year. “You could put in slightly different strains of Wolbachia,” she said. “It’s like getting a new insecticide.”
But she said that pathogens could increase their use of other, less efficient, kinds of mosquitoes. “If you eliminate Aedes aegypti from Australia, you still have Aedes albopictus,” she said. “Other mosquitoes who play minor roles could become a better vector once the niche is open. That’s how nature works.”
Tina Rosenberg won a Pulitzer Prize for her book “The Haunted Land: Facing Europe’s Ghosts After Communism.” She is a former editorial writer for The Times and the author, most recently, of “Join the Club: How Peer Pressure Can Transform the World” and the World War II spy story e-book “D for Deception.”
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2001年属什么生肖【李】【小】【花】【拿】【着】【一】【张】【红】【色】【的】【请】【帖】，【这】【是】【吴】【王】【府】【刚】【刚】【差】【人】【送】【过】【来】【的】。 【吴】【王】【久】【仰】【李】【小】【花】【的】【年】【少】【有】【为】，【把】【北】【地】【之】【王】【轩】【辕】【成】【艺】【的】【风】【雪】【庄】【连】【根】【拔】【除】，【为】【汉】【明】【扫】【除】【了】【北】【地】【之】【祸】，【因】【此】【知】【晓】【李】【小】【花】【来】【到】【青】【州】【府】【衙】【后】，【特】【意】【在】【吴】【王】【府】【设】【宴】【款】【待】，【为】【李】【小】【花】【接】【风】【洗】【尘】。 “【堂】【主】，【这】【吴】【王】【也】【实】【在】【太】【虚】【情】【假】【意】【了】，【知】【道】【大】【人】【要】【来】【青】【州】【府】，【不】【来】
【鹰】【听】【闻】【着】【耳】【边】【再】【次】【传】【来】【的】【声】【音】，【确】【认】【没】【有】【听】【错】，【转】【眼】【看】【向】【韩】【尘】【明】，【道】“【少】【城】【主】【让】【把】【他】【们】【都】【停】【下】！【城】【主】【要】【属】【下】【开】【木】【板】！” 【韩】【尘】【明】【一】【愣】，【随】【即】【道】“【都】【停】【下】！” 【鹰】【转】【身】【走】【到】【木】【板】【前】【扣】【住】【了】【木】【板】，【道】“【城】【主】【别】【担】【心】，【属】【下】【这】【就】【把】【木】【板】【打】【开】。” 【韩】【尘】【珠】【立】【即】【在】【角】【落】【里】【立】【即】【松】【了】【一】【口】【气】，【朝】【着】【鹰】【走】【了】【过】【去】。 【身】【后】【一】【个】
【再】【次】【见】【郭】【京】【云】，【事】【情】【办】【得】【很】【顺】【利】。 【她】【删】【除】【了】【自】【己】【保】【存】【的】【录】【音】，【郭】【京】【云】【也】【把】【解】【约】【书】【直】【接】【给】【她】【了】。 【临】【走】【之】【时】，【郭】【京】【云】【唤】【了】【她】：“【小】【鱼】，【我】【这】【里】【的】【大】【门】【随】【时】【为】【你】【敞】【开】。” 【时】【小】【鱼】【回】【身】：“【不】【求】【郭】【老】【板】【高】【抬】【贵】【手】，【只】【求】【郭】【老】【板】【在】【我】【所】【走】【的】【路】【上】【少】【放】【些】【绊】【脚】【石】，【我】【已】【感】【激】【不】【尽】【了】。” “【在】【你】【心】【里】，【是】【如】【此】【看】【我】【的】？
【楚】【天】【穆】【此】【行】【就】【是】【明】【知】【山】【有】【虎】【偏】【向】【虎】【山】【行】，【他】【这】【么】【孤】【注】【一】【掷】，【为】【的】【就】【是】【心】【中】【的】【那】【点】【不】【甘】【和】【不】【愿】，【到】【头】【来】【却】【落】【得】【个】【独】【守】【皇】【陵】，【坐】【着】【等】【死】【的】【下】【场】。 【随】【着】【帝】【后】【大】【婚】【和】【楚】【天】【穆】【造】【反】【一】【事】【结】【束】，【最】【受】【京】【城】【人】【关】【注】【的】【还】【有】【骠】【骑】【大】【将】【军】【新】【郡】【主】【的】【婚】【事】，【而】【此】【事】【也】【很】【快】【就】【被】【提】【上】【了】【日】【程】。 【这】【二】【人】【的】【婚】【礼】【最】【终】【订】【在】【了】【七】【月】【初】【七】，【刚】【好】【是】
【休】【息】【是】【没】【办】【法】【休】【息】【的】。 【这】【桩】【案】【子】【虽】【然】【完】【结】【了】，【但】【收】【尾】【工】【作】【还】【差】【许】【多】。 【毕】【竟】，【李】【瑞】【和】【许】【云】，【勾】【连】【出】【了】“【独】【品】”【犯】【罪】，【他】【们】【得】【联】【合】【缉】【毒】【大】【队】【一】【块】【儿】【把】【贩】【卖】【给】【许】【云】【和】【李】【瑞】【独】【品】【的】【那】【个】【团】【伙】【揪】【出】【来】，【再】【转】【交】【禁】【毒】【支】【队】。 【公】【安】【系】【统】【内】【的】【机】【构】【设】【置】【的】【还】【蛮】【复】【杂】【的】，【禁】【毒】【支】【队】【与】【刑】【侦】【支】【队】【平】【级】，【缉】【毒】【大】【队】【却】【又】【隶】【属】【刑】【侦】【支】【队】2001年属什么生肖【你】【对】【袜】【子】【的】【作】【用】【还】【停】【留】【在】【保】【暖】、【防】【寒】、【吸】【汗】【与】【防】【打】【滑】【上】【吗】？【那】【你】【只】【是】【一】【个】【普】【通】【的】【使】【用】【者】，【算】【不】【上】【顶】【尖】【的】【时】【尚】【达】【人】，【作】【为】【时】【尚】【的】【引】【航】【者】，【除】【了】【日】【常】【的】【使】【用】，【还】【有】【懂】【得】【利】【用】TA【吸】【睛】【赚】【眼】【球】。【近】【日】，【李】【菲】【儿】【就】【是】【利】【用】【袜】【子】【展】【现】【潮】【人】【风】【采】，【宽】【松】【上】【衣】+【皮】【裤】【帅】【气】【显】【瘦】【又】【时】【髦】，【露】【一】【截】【袜】【子】【抢】【眼】【十】【足】，【网】【友】【怒】【赞】：【李】【菲】【儿】【太】【有】【想】【法】【了】！
【滚】【滚】【洪】【音】【笼】【罩】【整】【个】【长】【安】【城】。 【城】【内】【聚】【集】【的】【魔】【门】【弟】【子】，【欢】【呼】【雀】【跃】，【恭】【迎】【声】【冲】【霄】【沸】【腾】。 【而】【反】【观】【那】【些】【还】【留】【存】【于】【城】【中】【的】【长】【安】【子】【民】、【屯】【戍】【军】【卫】、【王】【公】【贵】【族】，【却】【尽】【皆】【脸】【色】【惶】【恐】，【就】【如】【等】【待】【判】【决】【的】【羔】【羊】【一】【般】，【仰】【视】【着】【空】【中】【那】【威】【临】【大】【地】【的】【雄】【伟】【身】【躯】。 【魔】【皇】【来】【了】。 【驾】【龙】【而】【来】。 【即】【便】【已】【经】【见】【识】【过】【魔】【龙】【那】【无】【边】【恢】【弘】【的】【气】【焰】，【可】
【这】【是】【一】【片】【有】【着】【极】【少】【绿】【植】【的】【沙】【漠】【边】【缘】【地】【带】。 【此】【时】【的】【这】【片】【地】【带】【早】【已】【密】【布】【着】【多】【个】【势】【力】【的】【人】【手】，【大】【多】【都】【是】【三】【五】【人】、【七】【八】【人】【的】【样】【子】。 【但】【是】【也】【有】【聚】【集】【人】【数】【比】【较】【多】【的】，【足】【足】【有】【好】【几】【十】【人】【的】【样】【子】，【一】【看】【就】【是】【一】【方】【大】【势】【力】。 【更】【重】【要】【的】【是】，【从】【那】【些】【人】【身】【上】【散】【发】【出】【的】【气】【息】【来】【看】，【一】【看】【就】【知】【道】【不】【是】【普】【通】【人】。 【不】【过】【也】【确】【实】【是】【这】【样】，【只】
【两】【人】【都】【是】【初】【次】【恋】【爱】，【每】【每】【相】【处】【眼】【神】【对】【碰】【都】【能】【撞】【出】【火】【花】。【初】【尝】【相】【互】【喜】【欢】【的】【甜】【蜜】，【让】【小】【情】【侣】【恨】【不】【得】【天】【天】【黏】【在】【一】【起】。 【但】【是】【工】【作】【太】【忙】，【两】【人】【又】【不】【在】【一】【所】【学】【校】【教】【书】，【方】【音】【中】【学】【与】【离】【华】【高】【中】【相】【隔】【差】【不】【多】【有】【百】【里】，【坐】【车】【需】【要】【两】【三】【个】【小】【时】。 【两】【人】【只】【能】【在】【周】【末】【共】【聚】，【忙】【起】【来】【的】【时】【候】，【周】【末】【也】【见】【不】【上】【面】。【茉】【莉】【妍】【除】【了】【教】【语】【文】，【还】【当】【班】【主】
【那】【边】【不】【屑】【道】:“【你】【自】【己】【出】【门】【都】【会】【走】【丢】，【我】【看】【算】【了】【吧】。” 【萧】【唯】【一】【说】:“【可】【看】【她】【伤】【心】，【我】【有】【点】【于】【心】【不】【忍】。” 【那】【边】【说】【道】:“【这】【跟】【你】【有】【关】【吗】？【你】【有】【什】【么】【于】【心】【不】【忍】【的】？【人】【家】【找】【不】【找】【得】【到】【人】，【又】【不】【干】【你】【事】，【你】【别】【管】。” 【萧】【唯】【一】【不】【听】【劝】，【坚】【持】【道】:“【我】【自】【己】【会】【判】【断】【的】，【没】【事】【我】【先】【挂】【了】。” 【说】【完】【就】【结】【束】【了】【通】【话】 【向】【剑】【明】