Which animal SARS-COV-2 leapt from to infect human beings remains unknown. But the evidence suggests that bats were involved at some point —— perhaps not as the immediate source（译为：直接来源）of the virus, but probably as the reservoir from which it ultimately came（译为：最终来源）. Almost certainly that was true of the virus which caused the original SARS outbreak, in 2002.
leapt 是 leap 的过去分词
the evidence suggests that 有证据表明……
at some point 在某种程度上
reservoir n.水库；储藏，汇集
outbreak n.（疾病的）发作；（战争的）爆发 vi.爆发
epidemic outbreak 流行病爆发；爆发疫情
Though this was transmitted to people by palm civets（狸猫；椰子猫）, they probably caught it from horseshoe bats（菊头蝠）. MERS, another coronavirus, is similarly suspected of starting in bats, though the immediate source of human infection is camels（骆驼）.
Bats are also reckoned to be behind the spread of Ebola（埃博拉） and Marburg fevers（马尔堡热）, which are viral infections as well, though not caused by coronaviruses. And vampire bats （吸血蝠）famously carry another virus, rabies（狂犬病）.
viral infections 病毒感染
The idea that this may not be a coincidence has led people to ask if there is something special about bats which encourages the evolution within them of viruses predisposed to jump the species barrier and infect other sorts of animals. At the moment, the evidence is mixed.
predispose vt.使预先有倾向；使易接受，使易受感染，有……的倾向
predisposing factors 诱发因素；诱病因素
species barrier 物种屏障
In favour of the idea is an experiment conducted recently by Cara Brook of the University of California, Berkeley, and published in February in eLIFE. This suggests a possible 'mechanism（译为：机制，原理）. Some bats have unusual immune systems, in which an anti'viral （抗病毒的）process known as the interferon（干扰素） pathway is always active, rather than being switched on in response to infection（译为：而不是仅在感染时被激活）.
Dr Brook and her colleagues conducted experiments on cells from bats that have this arrangement and on others which do not (and also on cells from monkeys, as a control 作为对照). They concluded that always-on interferon pathways probably do speed up viral evolution. That would make bats more abundant sources of virulent new viruses than other groups of mammals.
virulent adj.有剧毒的，危险的，致命的；恶毒的，充满仇恨的
Against the idea, however, is work published this week in the Proceedings of the National Academy of Sciences by Nardus Mollentze and Daniel Streicker of the University of Glasgow.
Dr Mollentze and Dr Streicker found that the number of viruses which have passed to people from 11 orders （译为：目）of mammals and birds is pretty much proportional to the number of species in each order. Bats are the second-most diverse mammalian order, after rodents.
proportional adj.成比例的，相称的
proportion n.均衡；相称，协调；比例
mammalian n.哺乳动物 adj.哺乳动物的
rodent n.啮齿目动物
"It is therefore not surprising", Dr Mollentze observes, "that as a group they are associated with a large number of viruses." Although bat immune systems do indeed have the unusual features that interested Dr Brook and her colleagues, Dr Mollentze and Dr Streicker found no evidence these caused bat-associated viruses to be more numerous or more prone to infect people than viruses associated with other animal groups.
prone adj.易于……的；很可能的 prone position 卧姿
This study is in line with work done specifically on coronaviruses by Tracey Goldstein of University of California, Davis. In 2017 she and her colleagues published a piece of research in which they had tested for coronaviruses in bats, rodents and primates (including people) in 20 countries in Africa, South America and Asia. Individual bat species normally had between one and five types of coronavirus.
primate n.灵长类动物；大主教 adj.首要的，灵长动物的
(For comparison 作为比较, human beings have seven, including the newly emerged SARS-COV-2. ) Scale that up for（译为：扩大到） the 1,400 different species of the animals and it means there are potentially more than 3,000 coronaviruses circulating in bats.
This certainly increases the odds that bats will be responsible for generating a coronavirus dangerous to people. But only because there are lots of them.
odds n.不平等；几率；胜算；差别
odd adj.奇怪的；古怪的；单的；奇数的；临时的