Tropical Diseases Like Dengue Fever and Chikungunya Are on the Rise in Europe
Tropical Diseases Like Dengue Fever and Chikungunya Are on the Rise in Europe
登革热和基孔肯雅热等热带疾病在欧洲呈上升趋势
In September 2024, a handful of patients showed up at the emergency room in the coastal city of Fano, Italy, with mysterious symptoms: a rash on their hands and feet, fever, nausea, and diarrhea. Doctors sent for various tests until one came back with a positive result for dengue, a viral infection spread by mosquitoes, usually in tropical regions of the world. They tested the other patients, and, so enough, they had dengue too. The strange thing? None of the patients had recently traveled to a country where they might expect to pick up a dengue infection. The only thing they had in common was visiting a particular neighbourhood in Fano.
2024年9月，意大利沿海城市法诺（Fano）的急诊室接诊了几名患者，他们出现了神秘的症状：手脚皮疹、发烧、恶心和腹泻。医生进行了多项检查，最终其中一人被确诊为登革热——这是一种通常在世界热带地区通过蚊子传播的病毒性感染。医生随后对其他患者进行了检测，结果显示他们也都感染了登革热。奇怪的是，这些患者近期都没有去过可能感染登革热的国家。他们唯一的共同点是都曾去过法诺市的同一个街区。
As climate change increases temperatures across Europe, invasive mosquitoes are spreading and introducing disease agents that Europeans would usually think about only when traveling to other continents. The Fano outbreak wasn’t the first time dengue had been detected as spreading locally in mainland Europe, but it was significantly larger than previous incidents, with 199 cases detected between mid-August and mid-October of 2024. Over the past few years, European countries have reported outbreaks of other mosquito-borne viruses such as chikungunya, a painful disease that causes joint swelling, and West Nile virus. In a heating world, so-called tropical diseases are no longer restricted to tropical regions—and researchers expect the trend to continue.
随着气候变化导致欧洲气温升高，入侵性蚊子正在扩散，并带来了欧洲人通常只在前往其他大洲旅行时才会考虑的病原体。法诺的疫情并非欧洲大陆首次发现登革热本土传播，但其规模远超以往，2024年8月中旬至10月中旬期间共检测出199例病例。过去几年里，欧洲国家还报告了其他蚊媒病毒的爆发，例如会导致关节肿胀的疼痛性疾病——基孔肯雅热，以及西尼罗河病毒。在一个变暖的世界里，所谓的“热带疾病”已不再局限于热带地区，研究人员预计这一趋势还将持续。
The main current culprit is the mosquito Aedes albopictus, commonly known as the Asian tiger mosquito (or just the tiger mosquito, given it’s now found across all continents). Unlike many mosquito species, it bites in the daytime as well as at night. The tiger mosquito already has established populations across Europe, particularly in the south, and we can expect it to move north, says Riccardo Moretti, a senior researcher at the Italian National Agency for New Technologies, Energy and Sustainable Economic Development (ENEA), who has been working on tiger mosquitos for more than 20 years.
目前主要的罪魁祸首是白纹伊蚊（Aedes albopictus），俗称亚洲虎蚊（鉴于它现在遍布各大洲，也被简称为虎蚊）。与许多蚊子品种不同，它在白天和晚上都会叮咬人类。意大利国家新技术、能源和可持续经济发展局（ENEA）的高级研究员里卡多·莫雷蒂（Riccardo Moretti）表示，虎蚊已经在欧洲各地建立了种群，尤其是在南部地区，预计它还会向北迁移。莫雷蒂研究虎蚊已有20多年。
The tiger mosquito thrives between 20 and 30 degrees Celsius (68 to 86 Fahrenheit), but it can still live at around 10 Celsius (50 Fahrenheit). “This means that at the moment there are already conditions that could allow for the spread of the Asian tiger mosquito, even in England,” Moretti says. At the moment, these conditions are limited to the warmest part of the year in northern European countries. But farther south, such as in Greece, the mosquito season is elongating. Moretti says researchers have found adults buzzing around until December and reappearing already in March; they overwinter as eggs. “There is a concrete risk that in the next few years, we could have a population capable of surviving throughout the year,” Moretti says.
虎蚊在20到30摄氏度（68到86华氏度）的环境下生长最旺盛，但它在10摄氏度（50华氏度）左右也能存活。“这意味着目前即使在英国，也已经具备了亚洲虎蚊传播的条件，”莫雷蒂说。目前，这些条件在北欧国家仅限于一年中最温暖的时期。但在更南部的地区，如希腊，蚊子的活跃季节正在延长。莫雷蒂表示，研究人员发现成蚊在12月仍在活动，且3月份就已经再次出现；它们以卵的形式越冬。“未来几年，我们确实面临着蚊群能够全年存活的风险，”莫雷蒂说。
At the moment, cases of mosquito-borne diseases in Europe tend to occur toward the end of summer. This is when tiger mosquitoes are most prevalent, and it’s also when more people return from travel. Someone unwittingly brings back an infection that isn’t found in Europe—dengue, say—and gets bitten by a tiger mosquito. The mosquito goes on to bite other people, and the disease spreads locally. But as the weather cools, the mosquitoes get less active and cases subside. If the mosquito season lasts longer, however, more infections can occur. Ultimately, says Moretti, there’s a risk that tropical diseases like dengue could become endemic in parts of Europe, meaning the disease is always there. “It is completely different dealing with occasional cases of virus transmission, and instead dealing with a permanent status of possibility of transmission,” he says.
目前，欧洲的蚊媒疾病病例往往发生在夏末。这是虎蚊最猖獗的时候，也是人们结束旅行返程的高峰期。某人无意中带回了欧洲原本不存在的感染（比如登革热），然后被虎蚊叮咬。随后，这只蚊子再去叮咬其他人，疾病便在当地传播开来。但随着天气转凉，蚊子活跃度降低，病例也会随之减少。然而，如果蚊子的活跃季节延长，感染就会增多。莫雷蒂表示，最终存在一种风险，即登革热等热带疾病可能在欧洲部分地区成为地方性流行病，这意味着该疾病将长期存在。“应对偶尔发生的病毒传播病例，与应对持续存在的传播可能性，是完全不同的两码事，”他说。
A difference of a couple of degrees can make a big difference. Earlier this year, a study found that the conditions required for tiger mosquitoes to transmit chikungunya were cooler than previously thought. The mosquitoes can spread the virus at just 14 degrees Celsius (57 degrees Fahrenheit) rather than 16 (61 degrees Fahrenheit), meaning outbreaks could occur in most European countries and for longer periods. “That difference of two degrees matters a lot when we are talking about global warming,” says Sandeep Tegar, an epidemiological modeler at the UK Centre for Ecology and Hydrology, who led the study.
几度的温差可能会产生巨大的影响。今年早些时候的一项研究发现，虎蚊传播基孔肯雅热所需的条件比之前认为的要凉爽。蚊子在14摄氏度（57华氏度）时就能传播病毒，而非之前认为的16摄氏度（61华氏度），这意味着疫情可能在大多数欧洲国家发生，且持续时间更长。“当我们谈论全球变暖时，那两度的差异至关重要，”领导该研究的英国生态与水文学中心流行病学建模师桑迪普·特加（Sandeep Tegar）表示。
While warmer temperatures may generally create better conditions for mosquitoes, this isn’t the full story. Too hot—more than 35 degrees Celsius (95 degrees Fahrenheit)—and tiger mosquitoes struggle to survive. Southern France and Spain, impacted by recent heat waves and wildfires, may actually have fewer mosquitoes this year, says Frederic Bartumeus, an ecologist at the Spanish scientific research center CEAB: “It’s not been a great mosquito season in these areas, because it’s too hot and it’s too dry.”
虽然气温升高通常会为蚊子创造更好的生存条件，但这并非全部事实。如果气温过高（超过35摄氏度/95华氏度），虎蚊就难以生存。西班牙科学研究中心（CEAB）的生态学家弗雷德里克·巴图梅乌斯（Frederic Bartumeus）表示，受近期热浪和野火影响，法国南部和西班牙今年的蚊子数量反而可能减少：“这些地区的蚊子季节表现并不理想，因为天气太热、太干燥了。”
Rain is important, as mosquitoes need standing water to breed: This is where they lay their eggs, and where the larvae and pupae develop. “If it rains too little, then there’s not sufficient breeding sites,” explains Felipe Colón González, technology lead and expert in climate and infectious diseases at the UK-based health foundation Wellcome. “But if it rains too much, then it can wash away the mosquito breeding sites.” Humidity also plays a role. Beyond mosquitoes, climate conditions can have different effects on the viruses they carry, and on the behavior of humans—an important consideration in the spread of disease. This all makes modeling patterns of mosquitoes and the diseases they spread more complex, so ongoing surveillance is critical.
降雨也很重要，因为蚊子需要积水来繁殖：这是它们产卵的地方，也是幼虫和蛹发育的地方。“如果降雨太少，就没有足够的繁殖场所，”总部位于英国的健康基金会Wellcome的技术负责人、气候与传染病专家费利佩·科隆·冈萨雷斯（Felipe Colón González）解释道。“但如果雨下得太多，又会冲走蚊子的繁殖地。”湿度也起着一定作用。除了蚊子本身，气候条件还会对它们携带的病毒以及人类的行为产生不同影响——这是疾病传播中一个重要的考量因素。所有这些都使得蚊子及其传播疾病的模式建模变得更加复杂，因此持续的监测至关重要。
It may be possible to reduce mosquito populations if they’re caught early enough. ENEA’s Moretti is part of a team that recently ran an experiment to control a tiger mosquito population in Italy by releasing more than a million male mosquitoes that were reproductively incompatible—meaning when they mate, the female lays sterile eggs. This significantly reduced the number of fertile mosquito eggs in the area. But breeding mosquitoes in a specialized biofactory was expensive.
如果能及早发现，或许有可能减少蚊子种群。ENEA的莫雷蒂所在的团队最近在意大利进行了一项控制虎蚊种群的实验，他们释放了超过一百万只在生殖上不相容的雄性蚊子——这意味着当它们交配时，雌蚊产下的卵是无法孵化的。这显著减少了该地区可育蚊卵的数量。但在专门的生物工厂培育蚊子成本高昂。