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On July 14th America's Centres for Disease Control and Prevention (CDC) reported five new cases of the H5N1 avian flu virus in humans, bringing the total number of cases reported since April to nine.
7月14日，美国疾控中心(CDC)报告了5例新的人类H5N1禽流感病毒病例，自4月以来报告的病例总数已达9例。
All five were involved in culling infected poultry in Colorado, and appear to have the same strain that has been spreading in dairy cows across the country since December.
这5人都参与了科罗拉多州受感染家禽的扑杀，而且似乎感染了自12月以来在全国奶牛中传播的同一种毒株。
So far, there is no evidence the virus has adapted to spread between humans, a prerequisite for a flu pandemic.
到目前为止，没有证据表明该病毒已经适应了人与人之间的传播，而人与人之间的传播是流感大流行的先决条件。
But things can change quickly—the more the virus circulates in animals that come in close contact with humans, the bigger the risk that a pandemic strain will emerge.
但情况瞬息万变——病毒在与人类密切接触的动物中传播得越多，出现大流行毒株的风险就越大。
Should H5N1 go down this path, would the world be prepared? When sars-cov-2 emerged in 2019, humans had no natural immunity, drugs or vaccines.
如果H5N1走上这条路，世界会做好准备吗？当2019年sars-cov-2出现时，人类没有天然免疫力、药物或疫苗。
All three exist for H5N1, though how well any of them would work against a possible pandemic virus remains unclear.
这三种病毒都存在于H5N1中，但它们对潜在的大流行病毒的效果如何仍不清楚。
H5N1 was identified in wild geese in 1996 and has been circulating in birds ever since.
1996年，H5N1在野鹅中被发现，此后一直在鸟类中传播。
The virus is deadly for poultry and hundreds of millions of chickens have been culled over the decades to prevent its spread on farms.
这种病毒对家禽是致命的，几十年来，已有数亿只鸡被捕杀，以防止其在农场传播。
Occasionally, birds with H5N1 have infected mammals, including humans. Luckily, these have been dead-end infections, with no further spread.
感染H5N1的鸟类偶尔会感染哺乳动物，包括人类。幸运的是，这些感染路径都是死胡同，没有进一步传播。
In 2023, however, the H5N1 virus acquired genetic changes allowing it to spread between marine mammals.
然而，在2023年，H5N1病毒发生了基因突变，使其能够在海洋哺乳动物之间传播。
This is the kind of adaptation the virus needs to begin spreading between humans, says Malik Peiris, a virologist at the University of Hong Kong.
香港大学病毒学家裴伟士说，这是病毒开始在人与人之间传播所需要的适应性。
If the current outbreak in cows in America continues, he says, then mutations to ease its transmission between humans will almost certainly arise.
他说，如果目前美国奶牛的疫情持续下去，那么几乎肯定会出现缓解人与人之间传播的突变。
Alternatively, someone infected with a seasonal flu virus could become infected with a bovine H5N1.
或者，感染季节性流感病毒的人可能会感染牛H5N1。
That bovine H5N1 virus could then pick up the gene segments from the seasonal flu virus that makes it contagious between humans, a gene-swap trick that flu viruses are particularly adept at.
牛H5N1病毒随后可以从季节性流感病毒中获取基因片段，从而使其在人与人之间具有传染性，这是流感病毒特别擅长的基因交换。
Known as viral reassortment, this kind of swap happens particularly easily in pigs because they can become infected with both avian and human flu viruses simultaneously, acting as melting pots for viral evolution.
这种交换被称为病毒重配，在猪身上特别容易发生，因为它们可以同时感染禽流感病毒和人流感病毒，成为病毒进化的大熔炉。
H5N1 adapting to pigs is "the really scary thing" says Dirk Pfeiffer, a veterinary epidemiologist at the City University of Hong Kong.
香港城市大学兽医流行病学家德克·法伊弗（Dirk Pfeiffer）说，H5N1适应猪是“真正可怕的事情”。
Pigs infected with flu viruses are often asymptomatic, so by the time any H5N1 virus adapted to humans could be found in them, it would have already spread in people, he says.
他说，感染流感病毒的猪通常没有症状，因此当任何适应人类的H5N1病毒在猪身上发现时，它已经在人身上传播了。
The recent mammalian adaptations of H5N1, as well as its presence on dairy farms, make scientists think it is only a matter of time before it adapts to pigs.
H5N1最近在哺乳动物中的适应以及在奶牛场的传播，使科学家们认为它适应猪只是时间问题。
It is not possible to predict how deadly a pandemic strain of H5N1 could be. Since the virus first emerged, around 900 human infections have been confirmed.
无法预测H5N1大流行毒株的致命性。自该病毒首次出现以来，已确认约900例人类感染病例。
Half were fatal, but asymptomatic infections would have gone uncounted, making the true fatality rate lower.
一半是致命的，但无症状感染者不会被计算在内，因此实际死亡率较低。
The nine H5N1 cases in dairy and poultry workers found in America since April this year were all mild, though that will not necessarily hold true for future infections.
自今年4月以来，美国发现的9例奶牛和家禽工人H5N1病例均为轻度病例，尽管这不一定适用于未来的感染。
To understand how widespread human infections are, the CDCis now testing for antibodies in people on farms that have had H5N1 outbreaks.
为了解人类感染的广泛程度，CDC目前正在对爆发过H5N1疫情的农场人员进行抗体检测。
There are several reasons to believe that, should an H5N1 pandemic occur, things may be less dire than they were with covid-19. No one had immunity against covid when it emerged, for example.
有几个理由相信，如果发生H5N1大流行，情况可能不会像新型冠状病毒肺炎那样糟糕。例如，当新冠出现时，没有人对它有免疫力。
By contrast, studies suggest that most people have some degree of flu-related immunity that could prevent severe H5N1 infections.
相比之下，研究表明大多数人都具有一定程度的流感免疫力，可以预防严重的H5N1感染。
Antibodies for the flu are primarily directed against the two proteins on the surface of the influenza virus, hemagglutinin (H) and neuraminidase (N).
流感抗体主要针对流感病毒表面的两种蛋白质，即血凝素(H)和神经氨酸酶(N)。
