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过度洗手为什么可能致病?

彭博社 2018年06月26日

太爱干净,会除掉一些有益的微生物,增加人们患病风险。

JGI/Jamie Grill—Getty Images/Blend Images

即便在觉得自己是独自一人时,大家仍会有许多“伙伴”。实际上,在人携带的细胞中,只有大约一半属于人,剩下的都是微生物,比如细菌、真菌、原生动物和病毒。它们在人的体表或体内,这听起来似乎不利于健康,但大多数微生物对人都无害或者有益。许多研究者都认为,如果过度热衷于杀死“坏”微生物,一些不为人们所知的有益微生物也会被我们清除掉,从而破坏微生物群的多样性,它们统称为人体微生物菌群。有一种理论认为,这种现象是糖尿病、多发性硬化症和狼疮等免疫疾病最近在工业化国家抬头的部分原因。该理论引发了一系列新的研究,比如改善和这些“伙伴”的关系能否让这些疾病的发病率由升转降,再比如能否利用其中的一些微生物来提高人们的健康水平。

当前情况

科学发现迅速地把人体微生物和艾滋、肝炎等传染病、心脏病和癌症等非传染病乃至于孤独症、抑郁症等心理疾病联系在一起。这些发现让制药公司和学术实验室猛然出现了众多寻找可能治疗方法的研究,其思路通常是改变肠道微生物——约99%的人体微生物都生活在这里。一些最有希望的研究涉及粪菌移植,移植手段则包括结肠镜、内镜和灌肠剂灌入他人粪便。在初步人体临床试验中,粪菌移植展现出了潜力,可能成为治疗艰难梭菌感染复发的出色手段。医院经常出现这种病原体感染,而且美国每年约有3万人因此丧生。肥胖症一直是人们谈论的另一个充满吸引力的目标。在试验中,接受瘦老鼠粪菌的胖老鼠体重会变轻,反之亦然。

背景介绍

参与人体微生物项目(Human Microbiome Project)的研究者已经记录了1万多种人身上的微生物。这是一个国际性项目,由美国国立卫生研究院(U.S. National Institutes of Health)牵头。人的肠道内平均有大约38万亿个微生物,重量约0.2公斤。和欠发达国家的居民相比,工业化国家居民所携带微生物的多样性要低得多,人们认为首要原因是抗生素在医药和农业两个领域中的广泛使用。其他原因还包括自然分娩率和母乳喂养率较低——自然分娩和母乳喂养可将母亲的微生物传递给孩子,这也许能解释为什么剖腹产婴儿的哮喘和过敏发病率较高。只喝配方奶粉的婴儿患肥胖症和糖尿病的风险较高。社交、户外活动以及和动物的接触较少可能也会减少这些微生物的数量。多年来,科学家一直都知道和宠物犬一起长大会降低儿童患哮喘的可能性——一项研究称降幅可达13%,而且主要理由就是微生物多样性。看来抚摸爱犬以及被它舔舐可以让家庭成员进行微生物交换。

存在争议

研究者强调,开发基于微生物科学的治疗手段需要时间。同时,科学家们普遍认为,“放过”人体微生物对工业化国家的居民也许有好处。过度使用抗生素已被斥为增强细菌耐药性进而创造出超级细菌的原因,现在人们怀疑这样做会同时杀死人体肠道内的“好”细菌和“坏”细菌。医生们表示,他们经常为感染了病毒的患者开不必要的抗生素,原因是患者希望如此,而且也没有时间向他们解释可以杀死细菌的药对病毒毫无作用。美国开展了一项旨在减少病患要求的公开信息运动,医生开的抗生素数量随之下降。美国农民大量使用抗生素为牲畜治病防病。欧盟大多数国家的抗生素使用量则要低得多,欧盟已从2006年开始禁止对健康牲畜使用抗生素。改善微生物平衡的另一种可能途径是摄取名叫益生菌的“好”微生物。它们存在于酸奶、味噌、大豆饮料和膳食补充品中。一些研究者看到了益生菌的潜力,但他们的意见需要进一步检验,而且就摄取益生菌来满足各种需求而言,摄取多少以及摄取哪种益生菌都没有成熟的方案。(财富中文网)

译者:Charlie

审校:夏林

 

Even when you think you’re alone, you’ve got a lot of company. Of the cells you carry around, only about half, it turns out, are human. The rest belong to micro-organisms — bacteria, fungi, protozoans and viruses — that are on and inside you. That may sound unsanitary, but most of them are either harmless or beneficial. Many researchers think that in our overzealousness to kill bad germs, we’ve knocked off some underappreciated good ones, depleting the diversity of our microbiota, whose collective genes are known as the human microbiome. According to one theory, this has contributed to the recent increase, in industrialized countries, of autoimmune diseases such as diabetes, multiple sclerosis and lupus. That’s led to a spate of new research on whether a better relationship with our fellow travelers could undo that rise, and whether some of our microbes could be deployed to make us even healthier.

The Situation

Scientific findings have come quickly, connecting human microbiota to infectious diseases such as HIV and hepatitis, non-communicable ones like heart disease and cancer, and even psychiatric disorders such as autism and depression. The discoveries have sparked an explosion of research by drug companies and academic labs into possible treatments and cures. The idea, usually, is to alter organisms in the gut, where about 99 percent of human microbiota live. Some of the most promising research involves fecal transplantation — the introduction through colonoscopy, endoscopy or enema of a donor stool. In early human trials, it’s shown potential as a superior treatment for recurrent infection with C. difficile, a pathogen often contracted in hospitals that causes diarrhea and kills about 30,000 people a year in the U.S. Obesity has been discussed as another tantalizing target. In experiments, fat mice transplanted with microbes from thin mice lost weight and vice versa.

The Background

Researchers connected to the Human Microbiome Project, an international effort led by the U.S. National Institutes of Health, have catalogued more than 10,000 microbial species among our companion germs. The average human gut contains about 38 trillion microbes, weighing about 0.2 kilograms (0.4 pounds). Compared with people in less-developed countries, those in industrialized states have significantly less diversity in the microorganisms that populate their bodies. An excessive use of antibiotics, both in medicine and agriculture, is thought to be a leading cause. Lower rates of natural childbirth and breast feeding are others: Those practices pass microbes from mother to child, perhaps explaining why cesarean section babies have higher rates of asthma and allergies, and formula-fed babies are at an elevated risk of obesity and diabetes. Less socializing, outdoor activity and exposure to animals may also deplete microbiota. Scientists for years have known that growing up with a dog lowers a child’s chance of having asthma — by 13 percent, according to one study — and microbial diversity has become the leading explanation. Family members, it seems, swap microbes by petting their dogs and being licked by them.

The Argument

Researchers stress that therapies based on microbiome science will take time to develop. Meanwhile, there’s widespread agreement among scientists that people in industrialized countries would do themselves a favor by going easy on antibiotics. Already blamed for breeding resistance in bacteria and thus creating superbugs, antibiotic overuse is now a suspect in killing off good as well as bad bacteria in the human gut. Physicians say they often prescribe unnecessary antibiotics for viral infections because their patients expect it and there’s no time to explain that a bacteria killer won’t destroy a virus. A public-information campaign in the U.S. aimed at reducing patient demand has corresponded with a decline in antibiotic prescriptions. U.S. farmers use antibiotics intensively on livestock both to treat and prevent disease. Usage is much lower in most countries in the European Union, which has banned dosing healthy animals since 2006. Another possibility for encouraging a better microbial balance is to take in “good” microbes, called probiotics. They can be found in food such as yogurt, miso and soy beverages or in dietary supplements. Some researchers see potential in probiotics, but the case for them requires more investigation, and there are no established protocols for how much or what strains to consume for various purposes.

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