The US Has a Plan to Combat Screwworm. It Involves a Lot More Flies
The US Has a Plan to Combat Screwworm. It Involves a Lot More Flies
美国应对螺旋蝇的计划：投放更多的苍蝇
A flesh-eating parasitic fly that poses a major threat to livestock has returned to the United States after 60 years. This week, the US Department of Agriculture confirmed the presence of New World screwworm in a calf in southern Texas. 一种对牲畜构成重大威胁的食肉寄生蝇在消失60年后重返美国。本周，美国农业部证实，德克萨斯州南部的一头小牛身上发现了新大陆螺旋蝇。
Eliminated in the US in 1966 and as far south as Panama by 2006, its recent reemergence in Mexico made it likely that the screwworm would eventually enter the country again, with modeling showing that it could arrive as soon as summer 2025. It took slightly longer, but the screwworm has arrived. And to head off an outbreak, officials are deploying a tried-and-true technique: releasing lots and lots of adult screwworm flies. 螺旋蝇曾于1966年在美国被根除，并于2006年在南至巴拿马的地区被消灭。近期它在墨西哥的再次出现，使得人们预料到它终将再次进入美国，模型显示其最早可能在2025年夏季抵达。虽然比预期稍晚了一些，但螺旋蝇确实已经出现。为了防止疫情爆发，官员们正在部署一种久经考验的技术：大量释放成年螺旋蝇。
A screwworm infection occurs when a female fly lays its eggs in open wounds or other body parts of warm-blooded animals. When the eggs hatch, maggots emerge and feed on living tissue before turning into flies. As adults, screwworm flies do not bite or feed on flesh. Scientists in the 1930s and 1940s thought if they could prevent female flies from reproducing, they could break the cycle. At the time, New World screwworms killed hundreds of thousands of cattle annually, mostly in the American South and Southwest. 螺旋蝇感染发生在雌蝇将卵产在温血动物的开放性伤口或其他身体部位时。卵孵化后，蛆虫会钻出并以活体组织为食，随后发育成苍蝇。成年螺旋蝇不会叮咬或以肉为食。20世纪30年代和40年代的科学家认为，如果能阻止雌蝇繁殖，就能打破这一循环。当时，新大陆螺旋蝇每年导致数十万头牛死亡，主要集中在美国南部和西南部。
In the 1950s, researchers at the USDA made a breakthrough when they applied radiation to male screwworms and rendered them sterile. When released into an infected area, the sterile males mate with wild female insects and produce unviable eggs. No offspring are produced, and the population crashes. Known as sterile insect technique, it was first used successfully on the island of Curaçao, off the coast of Venezuela. It took just seven weeks to eliminate the pest, and the effort saved goat herds on the island that were a vital food source. 20世纪50年代，美国农业部的研究人员取得了一项突破：他们通过对雄性螺旋蝇进行辐射处理，使其失去生育能力。当这些不育雄蝇被释放到受感染地区时，它们会与野生雌蝇交配并产下无法孵化的卵。由于没有后代产生，该物种的种群数量会迅速崩溃。这种被称为“昆虫不育技术”的方法首次在委内瑞拉海岸外的库拉索岛成功应用。仅用了七周时间，该害虫就被彻底根除，这一努力拯救了岛上作为重要食物来源的山羊群。
The technique takes advantage of the fact that female New World screwworm flies only mate once in their lifetime. “The sterile insect technique is probably the most eloquent example of a completely successful biologic control mechanism,” says Sally DeNotta, associate professor of veterinary medicine at the University of Florida. “The life cycle stops. There’s no progeny produced. It’s been very successful.” 该技术利用了新大陆螺旋蝇雌蝇一生只交配一次的特性。“昆虫不育技术可能是生物控制机制完全成功的最有力例证，”佛罗里达大学兽医学副教授萨利·德诺塔（Sally DeNotta）表示，“生命周期停止了，没有后代产生。它非常成功。”
For years, the dense stretch of rainforest between Panama and Colombia known as the Darién Gap served as a biological barrier where sterile flies were released to prevent the northward spread of screwworm. But insects started breaking through the barrier in 2022. 多年来，巴拿马和哥伦比亚之间被称为“达连地堑”（Darién Gap）的茂密雨林一直作为一道生物屏障，通过在此释放不育苍蝇来阻止螺旋蝇向北蔓延。但从2022年开始，昆虫开始突破这一屏障。
To prevent an outbreak in South Texas, the USDA has blocked off a roughly 12-mile zone around the infected calf and is carrying out a targeted release of sterile screwworm flies from trucks. That’s in addition to the 4 million sterile flies per week already being air-dropped in the area. Anticipating the screwworm’s movement north, in February, the agency shifted its efforts to disperse 100 million sterile flies per week to focus on the area along the US-Mexico border. 为了防止德克萨斯州南部爆发疫情，美国农业部封锁了受感染小牛周围约12英里的区域，并正在通过卡车进行有针对性的不育螺旋蝇投放。这还不包括该地区每周已经通过空投投放的400万只不育苍蝇。由于预见到螺旋蝇会向北移动，该机构在2月调整了工作重点，每周投放1亿只不育苍蝇，重点覆盖美墨边境沿线地区。
“While this development is a serious threat to our livestock and wildlife, it hasn’t caught us off guard,” USDA secretary Brooke Rollins said during a House Agriculture Committee meeting on Thursday. She said around 400 million flies per week are needed to beat back screwworm. Currently, the US can only produce about 100 million flies per week at a facility located in Panama. “虽然这一事态发展对我们的牲畜和野生动物构成了严重威胁，但我们并未措手不及，”美国农业部长布鲁克·罗林斯（Brooke Rollins）周四在众议院农业委员会会议上表示。她指出，每周需要约4亿只苍蝇才能击退螺旋蝇。目前，美国位于巴拿马的一家设施每周只能生产约1亿只苍蝇。
A sterile insect facility in Mexico shut down in 2012, but the USDA is investing $21 million to help renovate and convert an existing fruit fly facility in Metapa, Mexico, to produce an additional 60 to 100 million sterile flies per week. That facility is expected to be operational this summer, according to the USDA. 墨西哥的一家昆虫不育设施于2012年关闭，但美国农业部正投资2100万美元，帮助翻新并改造位于墨西哥梅塔帕（Metapa）的一家现有果蝇设施，以期每周额外生产6000万至1亿只不育苍蝇。据美国农业部称，该设施预计将于今年夏天投入运营。
The agency is also fast-tracking the construction of a $750 million sterile fly facility at Moore Air Base in Edinburg, Texas, near the border with Mexico. That facility will not be up and running until November 2027. 该机构还在加快建设位于德克萨斯州爱丁堡（Edinburg）摩尔空军基地（Moore Air Base）的一家价值7.5亿美元的不育苍蝇设施，该基地靠近美墨边境。该设施要到2027年11月才能投入使用。
Screwworms do not infest meat, fruits, vegetables, or other food sources, but can infect people. Since 2023, there have been at least 2,070 human cases of screwworm in Mexico and Central America, according to the Centers for Disease Control and Prevention. 螺旋蝇不会寄生在肉类、水果、蔬菜或其他食物来源上，但会感染人类。据美国疾病控制与预防中心（CDC）统计，自2023年以来，墨西哥和中美洲已至少发生2070例人类感染螺旋蝇的病例。
DeNotta says she has no doubt that the US will eradicate it again, but says in the meantime, more cases could pop up. “A single female fly can lay hundreds to thousands of eggs at a time,” she says. “They’re able to travel to the next site and to the next host, so it’s very unlikely that this case is truly the only case.” 德诺塔表示，她毫不怀疑美国将再次根除这种害虫，但她同时也指出，在此期间可能会出现更多病例。“一只雌蝇一次可以产下数百到数千枚卵，”她说，“它们能够飞往下一个地点并寻找下一个宿主，因此这起病例极不可能是唯一的病例。”