Screwworms in US: Human risk is low—but they can burrow through your skull
Screwworms in US: Human risk is low—but they can burrow through your skull
美国出现螺旋蝇：人类感染风险虽低，但它们能钻透颅骨
Ravenous, flesh-eating flies have busted through containment barriers and have now reemerged in the US. On Monday and Tuesday, the US Department of Agriculture reported three new cases, bringing the tally to five. One of the cases is in a dog, though it’s unclear where it became infected; the dog lives in New Mexico, had its infection reported in Texas, and may have recently traveled to Mexico, where the flies are also spreading. But the other four US cases were all in Texas—and all in calves—two in Zavala County and two in La Salle County. 贪婪的食肉蝇已经突破了防御屏障，重新在美国出现。周一和周二，美国农业部报告了三起新病例，使总数达到五起。其中一起病例发生在一条狗身上，目前尚不清楚感染源；这条狗住在新墨西哥州，但在德克萨斯州报告了感染，且近期可能去过同样有疫情蔓延的墨西哥。其余四起美国病例均发生在德克萨斯州，且均为小牛——两起在扎瓦拉县（Zavala County），两起在拉萨尔县（La Salle County）。
Almost all the attention over screwworm’s resurgence has focused on the threat to livestock, like the calves and, in turn, the financial risk to the cattle industry. The fly’s voracious, screw-shaped larvae can fell cattle if given the chance, and preventing infestations requires intense vigilance. The USDA has estimated that if the flies stage a comeback rivaling isolated outbreaks of the past, they could cost Texas producers $732 million per year and the Texas economy $1.8 billion. 关于螺旋蝇卷土重来的关注几乎都集中在对牲畜（如小牛）的威胁上，进而关注到对养牛业的经济风险。这种苍蝇贪婪的螺旋状幼虫一旦有机会，就能击倒牛群，预防感染需要高度警惕。美国农业部估计，如果这些苍蝇的卷土重来达到过去局部爆发的规模，每年可能给德克萨斯州的生产者造成7.32亿美元的损失，并给德克萨斯州经济带来18亿美元的损失。
But while livestock are the easiest and costliest prey, humans are also at risk. Human cases are far less frequent than those in livestock, but when they do occur, they are just as severe. As researchers noted in a 2025 review, infestations in humans “cause rapidly enlarging, painful wounds that can progress to deeper tissues, with risks of secondary infection, sepsis, and mortality.” The fly’s larvae can destroy muscle, cartilage, and bone if they aren’t caught in time. They can even break through a human skull. 虽然牲畜是最容易受害且损失最惨重的目标，但人类也面临风险。人类病例远不如牲畜病例频繁，但一旦发生，后果同样严重。正如研究人员在2025年的一篇综述中所指出的，人类感染“会导致伤口迅速扩大、疼痛，并可能深入组织，伴有继发感染、败血症和死亡的风险。”如果不能及时发现，这种苍蝇的幼虫会破坏肌肉、软骨和骨骼，甚至能钻透人类的颅骨。
Human risk
人类风险
Understanding the threat requires examining the parasite’s lifecycle. The screwworm—technically New World screwworm or Cochliomyia hominivorax (Coquerel)—is a parasitic blowfly. Females mate only once in their 10–30-day lifespan but can lay up to 3,000 eggs. The flies are attracted to the smell of wounds, mucous membranes, and orifices of warm-blooded animals, and females deposit hundreds of eggs when they find an opening. The eggs hatch within a day, and the resulting eponymous screw-shaped larvae quickly begin ruthlessly boring into and feasting on their victim’s living flesh. This savagery can last up to a week before the mature larvae fall to the ground. There, they pupate in the soil and emerge, 7–54 days later, as adult flies. 了解这一威胁需要审视该寄生虫的生命周期。螺旋蝇（学名为新大陆螺旋蝇或 Cochliomyia hominivorax）是一种寄生性丽蝇。雌蝇在10至30天的寿命中只交配一次，但可产下多达3000枚卵。这种苍蝇会被温血动物伤口、粘膜和孔窍的气味所吸引，一旦找到开口，雌蝇就会产下数百枚卵。卵在一天内孵化，随后产生的螺旋状幼虫会迅速开始无情地钻入并啃食受害者的活体组织。这种残忍的过程可持续长达一周，直到成熟的幼虫落到地面。随后，它们在土壤中化蛹，7至54天后羽化为成蝇。
This sequence of events used to occur regularly in the US and Central America; screwworm was endemic here but was eradicated after a concerted, decades-long campaign to annihilate its populations. This was done using Sterile Fly Technique, which involves breeding millions of male flies in specialized facilities, sterilizing them with gamma radiation, then dropping them from the air like bombs. It works by exploiting the fact that females mate only once; if they do so with a sterile male, there will be no offspring, and the population will collapse. 这一过程过去常在美国和中美洲发生；螺旋蝇曾是当地的流行病，但在经过数十年的协同灭绝行动后被根除。这是通过“不育蝇技术”实现的，即在专门设施中培育数百万只雄蝇，用伽马射线使其绝育，然后像炸弹一样从空中投放。其原理是利用雌蝇只交配一次的特性；如果它们与不育的雄蝇交配，就不会产生后代，从而导致种群崩溃。
Screwworms were eradicated from the US Southwest in 1966, though Texas continued to struggle with outbreaks into the 1980s. Mexico declared eradication in 1991, and efforts to zap the flies continued moving southward. Panama declared eradication in 2006, and for years, the flies were held at bay at the Darién Gap, the border of Panama and Colombia, with consistent sterile male fly releases. But around 2022, the barrier was breached, and the flies have been eating their way back up. With the northward movement, reports of human cases of screwworm infections, called myiasis, have trailed them in Central America. They offer a glimpse of the risk that people in the US now face as the flies invade. 1966年，美国西南部根除了螺旋蝇，尽管德克萨斯州在20世纪80年代仍持续受到疫情困扰。墨西哥于1991年宣布根除，消灭苍蝇的努力继续向南推进。巴拿马于2006年宣布根除，多年来，通过持续投放不育雄蝇，这些苍蝇被阻挡在巴拿马和哥伦比亚边境的达连地峡（Darién Gap）。但大约在2022年，这一防线被突破，苍蝇开始一路向北“吃”回来。随着它们向北移动，中美洲出现了被称为“蝇蛆病”（myiasis）的螺旋蝇感染人类病例报告。这些病例让我们得以一窥随着苍蝇入侵，美国民众现在所面临的风险。
Human cases emerge
人类病例出现
Screwworms will attack any wound in humans—they can find a wound as tiny as a tick bite as a way in. For those caught unaware, the flies will also happily lay eggs in convenient openings such as the nose, mouth, ears, eyes, and even the bum, if available. In early 2024, researchers in Costa Rica—which declared screwworm eradicated in 2000—reported what is thought to be the first identified human myiasis case in the country since the reemergence. The case was in a 71-year-old man from a small rural community close to the border with Panama. He sought care on January 12, 2024, for wounds on his feet, specifically between his toes, which had developed over the prior four months. The wounds had painful, oozing pus and smelled horrible. Doctors noticed a deep lesion between the first two toes on his right foot. They pulled out approximately 160 screwworm larvae. 螺旋蝇会攻击人类身上的任何伤口——哪怕是像蜱虫叮咬那样微小的伤口，它们也能找到入口。对于毫无防备的人，如果鼻孔、口腔、耳朵、眼睛甚至臀部等部位有开口，苍蝇也会乐于在这些地方产卵。2024年初，哥斯达黎加（该国于2000年宣布根除螺旋蝇）的研究人员报告了自疫情卷土重来以来，该国首例被确认的人类蝇蛆病病例。患者是一名来自靠近巴拿马边境农村社区的71岁男子。2024年1月12日，他因脚部（特别是脚趾间）在过去四个月内形成的伤口寻求治疗。伤口疼痛、流脓且散发出恶臭。医生注意到他右脚前两个脚趾之间有一个深层病灶，并从中取出了大约160条螺旋蝇幼虫。
The man was sent to an emergency department for wound care, where doctors found some more larvae. He was also diagnosed with two bacterial infections, Staphylococcus aureus and Pseudomonas aeruginosa. He was treated with antibiotics and creams and had healed by the time of his six-week follow-up. In February 2024, a month after the man’s case, Costa Rica declared a national emergency over the screwworm resurgence. By October 10, 2024, the country had logged 8,671 animal cases and 33 human cases. Of those human cases, three died. The cases were said to be in people with significant underlying health conditions, including organ and immune system dysfunction, as well as debilitation. At that point, Panama, to the south, had 18,553 animal and 79 human cases. And to the north, things were starting to pick up in Nicaragua, with 3,307 animal and two human cases. In Honduras, there were just 15 animal cases. 该男子被送往急诊科进行伤口护理，医生又发现了更多幼虫。他还被诊断出患有两种细菌感染：金黄色葡萄球菌和铜绿假单胞菌。经过抗生素和药膏治疗，他在六周后的复查时已经痊愈。2024年2月，即该病例发生一个月后，哥斯达黎加因螺旋蝇卷土重来宣布进入国家紧急状态。截至2024年10月10日，该国记录了8671例动物病例和33例人类病例。在这些人类病例中，有3人死亡。据称，这些患者均患有严重的潜在健康问题，包括器官和免疫系统功能障碍以及身体虚弱。当时，南部的巴拿马有18553例动物病例和79例人类病例。而在北部，尼加拉瓜的情况也开始加剧，有3307例动物病例和2例人类病例。洪都拉斯则仅有15例动物病例。
Clinical horrors
临床恐怖
In March 2025, doctors in Canada reported that a resident in his 80s returned home from a trip to Costa Rica with myiasis. He had fallen during the trip, scraping up both knees and shins. While the wounds mostly seemed to heal, an ulcer formed on his right shin. He sought care while still in Costa Rica, and doctors there extracted 30–40 larvae. 2025年3月，加拿大医生报告称，一名80多岁的居民从哥斯达黎加旅行归来后患上了蝇蛆病。他在旅行中摔倒，双膝和胫骨擦伤。虽然伤口大部分似乎已经愈合，但他的右胫骨上形成了一个溃疡。他在哥斯达黎加时曾寻求治疗，当地医生取出了30至40条幼虫。