譯/李京倫
新冠病毒如何偷走嗅覺
Few of COVID-19's peculiarities have piqued as much interest as anosmia, the abrupt loss of smell that has become a well-known hallmark of the disease.
COVID patients lose this sense even without a stuffy nose; the loss can make food taste like cardboard and coffee smell noxious, occasionally persisting after other symptoms have resolved.
少有新冠肺炎的特點像嗅覺喪失一樣激起那麼多關注。嗅覺喪失是突然失去嗅覺，已成為這種疾病眾所周知的特徵。新冠肺炎患者甚至沒有經歷鼻塞就失去嗅覺。失去嗅覺會讓食物嘗起來像硬紙板，咖啡氣味難聞，這種症狀偶爾會在其他症狀消退後持續。
Scientists are now beginning to unravel the biological mechanisms, which have been something of a mystery: The neurons that detect odors lack the receptors that the coronavirus uses to enter cells, prompting a long debate about whether they can be infected at all.
科學家現在開始弄懂這個向來可說是個謎的生物機制：感知氣味的神經元並無受體供新冠病毒用來進入細胞，引發關於這些神經元究竟能否被感染的長期爭論。
Insights gleaned from new research could shed new light on how the coronavirus might affect other types of brain cells, leading to conditions like "brain fog," and possibly help explain the biological mechanisms behind long COVID — symptoms that linger for weeks or months after the initial infection.
從新近研究收集來的洞見或許能進一步闡明，新冠病毒如何侵襲其他種類的腦細胞，導致「腦霧」等症狀出現，而且或許能解釋新冠長期症狀的生物機轉。新冠長期症狀是在最初感染後持續數周或數月的症狀。
The new work, along with earlier studies, settles the debate over whether the coronavirus infects the nerve cells that detect odors: It does not. But the virus does attack other supporting cells that line the nasal cavity, the researchers found.
除了稍早的研究之外，新研究也解決了關於新冠病毒會不會侵擾察覺氣味的神經細胞爭論。答案是不會。不過，研究人員發現，新冠病毒攻擊的是位在鼻腔內側的其他支持細胞。
The infected cells shed virus and die, while immune cells flood the region to fight the virus. The subsequent inflammation wreaks havoc on smell receptors, proteins on the surface of the nerve cells in the nose that detect and transmit information about odors.
被感染的細胞擺脫病毒後死亡，同時免疫細胞蜂擁到這個區域對抗病毒。隨後的發炎嚴重破壞嗅覺受體，即鼻內神經細胞表面能察覺並傳達氣味資訊的蛋白質。
The process alters the sophisticated organization of genes in those neurons, essentially short-circuiting them, the researchers reported.
研究人員說，這個過程改變了這些神經元基因的複雜組織，實質上使神經元基因短路。
Their paper significantly advances the understanding of how cells critical to the sense of smell are affected by the virus, despite the fact that they are not directly infected, said Dr. Sandeep Robert Datta, an associate professor of neurobiology at Harvard Medical School, who was not involved in the study.
並未參與這分研究的美國哈佛大學醫學院神經生物學副教授達塔博士說，他們的論文大幅增進了這方面的了解：對嗅覺至關重要的細胞儘管不會被新冠病毒直接感染，卻會被新冠病毒侵襲。
"It's clear that indirectly, if you affect the support cells in the nose, lots of bad things happen," Datta said. "The inflammation in the adjacent cells triggers changes in the sensory neurons that prevent them from working properly."
達塔說：「顯然，如果你攻擊鼻子的支持細胞，有很多壞事會間接發生。鄰近細胞發炎會引起感覺神經元改變，使感覺神經元無法正常工作。」
Indeed, many complications of COVID appear to be caused by the immune system's friendly fire as it responds to infection by flooding the bloodstream with inflammatory proteins called cytokines.
的確，許多新冠肺炎併發症似乎由免疫系統對自己人的攻擊引起，因為免疫系統應付感染的方式是讓血液中充滿名為細胞激素的發炎蛋白質。
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