New Weapon to Fight Zika: The Mosquito
Every weekday at 7 a.m., a van drives slowly through the southeastern Brazilian city of Piracicaba carrying a precious cargo — mosquitoes. More than 100,000 of them are dumped from plastic containers out the van’s window, and they fly off to find mates.
But these are not ordinary mosquitoes. They have been genetically engineered to pass a lethal gene to their offspring, which die before they can reach adulthood. In small tests, this approach has lowered mosquito populations by 80 percent or more.
The biotech bugs could become one of the newest weapons in the perennial battle between humans and mosquitoes, which kill hundreds of thousands of people a year by transmitting malaria, dengue fever and other devastating diseases and have been called the deadliest animal in the world.
“When it comes to killing humans, no other animal even comes close,” Bill Gates, whose foundation fights disease globally, has written.
The battle has abruptly become more pressing by what the World Health Organization has called the “explosive” spread of the mosquito-borne Zika virus through Brazil and other parts of Latin America. Experts say that new methods are needed because the standard practices — using insecticides and removing the standing water where mosquitoes breed — have not proved sufficient.
世界卫生组织(World Health Organization)称蚊媒传播的兹卡病毒在巴西及拉丁美洲的其他地方出现“爆炸式”传播，从而使这场斗争突然变得更加紧迫。专家们表示，需要新方法，因为事实证明，使用杀虫剂及清除蚊子赖以繁衍的积水等常用作法不够有效。
“After 30 years of this kind of fight, we had more than two million cases of dengue last year in Brazil,” said Dr. Artur Timerman, an infectious disease expert in São Paulo. “New approaches are critically necessary.”
But the new efforts have yet to be proved, and it would take some years to scale them up to a meaningful level. An alternative to mosquito control, a vaccine against Zika, is not expected to be available soon.
So for now, experts say, the best modes of prevention are to intensify use of the older methods of mosquito control and to lower the risk of being bitten using repellents and by wearing long sleeves.
Women are being advised to not get pregnant and to avoid infested areas if pregnant, since the virus is strongly suspected of causing babies to be born with abnormally small heads and damaged brains.
One old method that is not getting serious attention would be to use DDT, a powerful pesticide that is banned in many countries because of the ecological damage documented in the 1962 book “Silent Spring.” Still, it is being mentioned a bit, and some experts defend its use for disease control.
“That concern about DDT has to be reconsidered in the public health context,” said Dr. Lyle R. Petersen, director of the division of vector-borne diseases at the Centers for Disease Control and Prevention. He said the damage to fish and wildlife stemmed from widespread outdoor use of DDT in agriculture, not the use of small amounts on walls inside homes to kill mosquitoes.
“从公共卫生方面来看，对滴滴涕的这一担忧需要重新考虑，”美国疾病控制与预防中心（Centers for DiseaseControl and Prevention，简称CDC）媒传疾病部主任莱尔·R·彼得森博士(Lyle R. Petersen)说。他表示，有害于鱼类和野生动物的是农业领域在室外广泛使用滴滴涕的做法，而不是向室内墙壁喷洒少量滴滴涕来消灭蚊子的行为。
Other experts say the old methods can work if applied diligently.
“We’ve had great success using old methods for the last 50, 60 years,” said Dr. Peter J. Hotez, dean of the National School of Tropical Medicine at the Baylor College of Medicine. “We just need to be very aggressive and exercise political will.”
“我们在过去五六十年中使用老方法取得了巨大成功，”美国贝勒医学院国家热带疾病学院(National School of Tropical Medicine the Baylor College of Medicine)院长彼得·J·霍特兹博士(Peter J. Hotez)说。“我们只需要非常积极地行动，践行政治意愿。”
The main mosquito that transmits Zika virus — and also dengue, chikungunya and yellow fever — is Aedes aegypti, a particularly wily foe.
It prefers urban areas and bites mainly people, making it very efficient at spreading disease. It bites in the day, so bed nets, a common way to protect people against the night-biting malaria mosquitoes, have little effect. It breeds in small containers of water, such as flower pots, cans and tires that collect rainwater.
“I’ve seen Aedes aegypti merrily breeding in discarded soda caps,” said Joseph M. Conlon, technical adviser to the American Mosquito Control Association.
美国控蚊协会(American Mosquito Control Association)技术顾问约瑟夫·M·康伦(Joseph M. Conlon)说，“我看到埃及伊蚊可以欢快地在汽水瓶盖里繁殖。”
Aedes aegypti is found in the southern part of the United States, so public health authorities say there will be some local transmission of Zika in this country, though it will be far less serious than in Latin America. Dr. Petersen of the C.D.C. said he envisioned “almost a SWAT team approach” in which resources would be rapidly deployed to areas of local transmission to control mosquitoes using conventional methods.
The genetically engineered Aedes aegypti mosquitoes were developed by Oxitec, a British company, to fight dengue, but would also work to curtail the spread of Zika.
Since last April, the mosquitoes have been released in one neighborhood of Piracicaba populated by about 5,000 people. By the end of 2015, there was a reduction in wild mosquito larvae — as opposed to larvae inheriting the lethal gene — of 82 percent, the company said.
But critics worry about the long-term effects of releasing genetically modified organisms. Oxitec has run into public opposition to a proposed test in the Florida Keys.
A Brazilian commission that oversees genetically engineered organisms declared the Oxitec mosquitoes safe to release into the environment in 2014. But Oxitec still does not have a license from Brazil’s health regulators that would allow it to actively market its approach to Brazilian cities.
Still, said Hadyn Parry, the company’s chief executive, with the outbreak of Zika, “We’ve had a huge amount more interest from different municipalities.”
Another approach, being tested in one Rio de Janeiro neighborhood, is to infect the mosquitoes with Wolbachia, a bacterium that does not infect them naturally. Once infected, the mosquitoes do not pick up and transmit viruses as easily.
The bacteria can be passed to the next generation through eggs, so they spread through the mosquito population.
“The beauty of it is it is a sustainable method — once you put it out it sustains itself in the environment and gives ongoing protection,” said Scott O’Neill, dean of science at Monash University in Australia. He is the leader of Eliminate Dengue, a Wolbachia project supported by the Bill & Melinda Gates Foundation and others.
“这种方法好就好在它的可持续性，一旦释放，就可以在环境中延续下去，不断给予保护，”澳大利亚莫纳什大学(Monash University)科学院院长斯科特·奥尼尔(Scott O’Neill)说。他是“消除登革热”(Eliminate Dengue)项目的带头人。该项目利用沃尔巴克氏菌，获得了比尔及梅林达·盖茨基金会(Bill and Melinda Gates Foundation)等机构的支持。
Tests are now underway in Indonesia and Vietnam to see if the technique can reduce the number of people getting dengue fever.
Dr. Paulo Gadelha, president of the Oswaldo Cruz Foundation, a scientific institute under the Brazilian Ministry of Health, said initial results in his country were good and there were plans to try it on a larger scale, in Niterói, a municipality across Guanabara Bay from Rio.
巴西卫生部旗下科研机构奥斯瓦尔多·克鲁兹基金会(Oswaldo Cruz Foundation)的主席保罗·贾德勒哈博士(Paulo Gadelha)表示，在他们国家开展的试验的初步结果较好，有在尼泰罗伊进行更大规模试验的计划。这座自治市与里约隔着瓜纳巴拉湾相望。
“We are planning to scale this up,” he said. “The mayor has already agreed.”
A new and even more powerful tool may be gene drives, which are genetic mechanisms that rapidly propagate a trait through a wild population. Just in the last few months, scientists have made gene drives that work in mosquitoes in the laboratory.
Anthony A. James, a professor at the University of California, Irvine, said it would be straightforward to use a gene drive to spread something like a sterility trait through the Aedes aegypti population to kill them off.
加州大学欧文分校(University of California, Irvine)教授安东尼·A·詹姆斯(Anthony A. James)表示，通过基因驱动在埃及伊蚊群体中传播不育性状以消灭蚊子的做法直截了当。
“We have all the blueprints and have demonstrated proofs of principle,” he said. “It’s just public will to do this.”
The public might not be ready to deploy gene drives outside the laboratory because once a new trait is let loose to spread through the population, it would be difficult to reverse it if something went wrong.
Dr. Petersen of the C.D.C. said of all the new approaches, “We don’t know about the efficacy of any of them on a wide enough scale.” He added, “For now, we’ve got to deal with what we have.”