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Science and technology: Medical treatment: Feed a virus, starve a bacterium
科學與技術：醫療：感染病毒時進食，感染細菌時禁食
An old wives’ tale gets some support from medical science.
無稽之談獲醫學證實。
Whether it is best to feed a fever and starve a cold, or vice versa, varies with the grandparent being asked.
要說是發燒時宜吃，傷風時宜餓呢，還是反之為佳？不同的祖父母回答是不一樣的。
Medicine has decided that it is always a bad idea to deny food to the ill.
醫療界已經判定，生病時拒絕進食總非良策。
Now a new study suggests that by ignoring such old wives’ tales, medics may have missed a trick.
現有一項新研究表明，若忽視這類無稽之談，醫療人員可能會錯過機會。
A paper just published in Cell by a team of researchers led by Ruslan Medzhitov at Yale University suggest that force-feeding mice infected with influenza keeps them alive—but doing the same to mice with bacterial infections is fatal.
由耶魯大學魯斯蘭·麥哲托夫帶領的團隊近日在《細胞》上發表的研究表明，患有流感的老鼠受到強行喂食尚能活命，而對有細菌感染的老鼠卻是致命的。
Dr Medzhitov was inspired by experiments conducted not by medics, but by zoologists.
麥哲托夫博士受到動物學家 (而非醫生) 所做的實驗啟發。
Most animals instinctively respond to infection by cutting back on food, and a slew of studies in recent years have shown that when diseased animals are force-fed they are more likely to die than if they are allowed to abstain.
大多數動物受到感染后，會本能地減少進食，并且近年來大量研究表明，強制給生病的動物喂食比允許其抑制進食更易致死。
But Dr Medzhitov wondered whether that held true for all types of disease.
但麥哲托夫博士好奇這是否適用于各類疾病。
To investigate, he and his team infected one group of mice with a murine influenza virus, and the other with Listeria monocytogenes, a bacterium that causes food poisoning.
為了進一步調查，麥哲托夫博士和他的團隊使一組老鼠感染流感病毒，另一組感染能引發食物中毒的李斯特菌。
Some mice in each group were force-fed rodent chow, while others were force-fed nutrition-free saline.
每組中，給一部分老鼠強迫喂食鼠類飼料，而給另一部分老鼠注射無營養的生理鹽水。
Every single mouse that was infected with the bacterium died if they were given food, but half survived on the saline.
感染細菌又被強迫喂食物的老鼠全部死亡，而被注射生理鹽水的老鼠存活率達到一半。
The results of the viral infection were less stark, but still clear: 77.8% of infected mice survived if given food, but only 10% did so when given saline.
雖然病毒實驗結果不那么殘酷，但依然分明：其中被強迫喂食的老鼠存活率77.8%，而被注射生理鹽水的老鼠存活率僅為10%.
One clue as to what might be going on lies in the fact, identified in earlier research, that cells infected with bacteria often prefer to burn fat instead of glucose, their usual fuel.
導致這個結果可能的原因之一就在于受細菌感染的細胞通常傾向于燃燒脂肪而非葡萄糖 (平常的燃料)，這也得到早期研究的證實。
Further experiments led the team to confirm that glucose specifically was the key to survival in both viral and bacterial infections.
進一步的實驗使團隊確定，葡萄糖在病毒感染和細菌感染中起到了性命攸關的作用。
As with the rodent chow, mice with bacterial infections that were fed glucose died.
對感染細菌的老鼠喂食物或葡萄糖都致死。
But infected mice fed a version of glucose that they could not metabolise lived.
但當感染細菌的老鼠被喂食一類無法參與新陳代謝的葡萄糖時反而存活。
Again, those results were nearly reversed in mice suffering from a viral infection.
然而，受到病毒感染的老鼠結局幾乎相反。
All of those fed the unusable variant of glucose died within ten days; 40% of those fed the ordinary stuff survived.
被喂食無法食用的變異葡萄糖的老鼠在10天之內全部死亡，喂食普通食物的老鼠中則有40%存活下來。
The glucose seemed to make no difference to the bugs, nor to the immune systems of the mice.
葡萄糖似乎對輕微的傳染病和老鼠的免疫系統沒有什么影響。
Instead, it altered the biology of the infected cells.
相反，它轉變了受感染細胞的機理。
In viral infections, many infested cells were committing suicide, a cellular scorched-earth strategy designed to slow the spread of the virus.
在病毒感染中，許多受感染的細胞都在自殺，這種焦土政策旨在減緩病毒的傳播。
Providing glucose seemed to bolster their ability to fight the infection without resorting to such drastic measures.
而葡萄糖似乎只想要加強他們對抗感染的能力，而非訴諸于自殺這種極端的措施。
The opposite was true for bacteria. Burning fat protected infected mice.
相反，葡萄糖對細菌感染影響重大。燃燒脂肪保護了受感染的老鼠。
But swamping the cells with glucose caused them to produce prodigious quantities of highly reactive chemicals known as free radicals, which damage cells.
但給細胞灌滿葡萄糖會使它們產生數量龐大的高度活躍化學物質，即破壞細胞的自由基。
That collateral damage made survival less likely.
這種附帶損害使老鼠更難存活。
The precise biological details of why glucose is good for viral infections and bad for bacterial ones are not yet known.
葡萄糖對病毒感染有益卻對細菌感染有害的具體生物學細節還尚未可知。
And Dr Medzhitov’s results will have to be tested in humans before medics can apply them.
在醫護人員運用研究結果之前，麥哲托夫博士仍需要做臨床試驗。
But they are a useful reminder that there is sometimes genuine wisdom hidden in folksy homilies.
但這些成果依然有效地提醒人們：有時候民間俗語中還是蘊含著大智慧的。
