Researchers are seeking to learn why bird flu kills some animals quickly but causes only moderate illness in others.[qh]

研究人员正在研究为什么禽流感会迅速杀死一些动物，但在其他动物中仅会引起中度疾病。[qh]

In recent years, bird flu is believed to have killed millions of wild and domestic birds worldwide.[qh]

近年来，禽流感被认为已在全球范围内导致数百万只野生鸟类和家禽死亡。[qh]

Other animals such as seals, cats, dogs and cows have also been infected. [qh]

其他动物，如海豹、猫、狗和牛也被感染了。[qh]

The virus is officially known as H5N1. It has largely stayed out of the human population.[qh]

该病毒正式名称为H5N1。它在很大程度上远离了人类。[qh]

However, the World Health Organization (WHO) reported that as of April 1, 2024, H5N1 had caused nearly 900 human infections and 463 deaths since 2003.[qh]

然而，世界卫生组织报告称，自2003年以来，截至2024年4月1日，H5N1已导致近900人感染，463人死亡。[qh]

Most of the human cases involved direct contact between people and infected birds.[qh]

大多数人类病例涉及人与受感染鸟类之间的直接接触。[qh]

In cases of the virus spreading between humans, individuals involved were found to have had close and extended contact within households.[qh]

在病毒在人与人之间传播的案例中，涉案人员被发现在家庭内有过密切和长时间的接触。[qh]

The currently spreading version of bird flu was first identified in 1959.[qh]

目前正在传播的禽流感版本于1959年首次被确认。[qh]

But the illness did not start to cause concern among health officials until a bird flu outbreak hit Hong Kong in 1997.[qh]

但直到1997年禽流感爆发袭击香港，这种疾病才开始引起卫生官员的关注。[qh]

That outbreak caused severe sickness and deaths in some humans.[qh]

那次疫情爆发导致了一些人患上严重疾病并且造成了死亡。[qh]

Scientists are still studying possible reasons the H5N1 virus has not heavily affected human populations.[qh]

科学家们仍在研究H5N1病毒没有对人类造成严重影响的可能原因。[qh]

But some researchers fear the situation may change. Like other viruses, H5N1 has mutated over time.[qh]

但是一些研究人员担心情况可能会发生改变。像其他病毒一样，H5N1会随着时间的推移发生变异。[qh]

During the last few years, one particular bird flu version has been spreading quickly and widely.[qh]

在过去的几年里，一种特定的禽流感病毒体一直在迅速而广泛地传播。[qh]

Dr. Tom Frieden is a former director of the U.S. Centers for Disease Control and Prevention (CDC).[qh]

汤姆·弗里登博士是美国疾病控制与预防中心（CDC）的前主任。[qh]

He told The Associated Press about the ongoing outbreaks, “There's a lot we don't understand.”[qh]

他对美联社谈到正在发生的疫情时说：“有很多我们不了解的地方。”[qh]

Frieden also heads the non-profit group Resolve to Save Lives.[qh]

弗里登还领导着非营利组织“决心拯救生命”。[qh]

He added, “I think we have to get over the 'hope for the best and bury our head in the sand' approach."[qh]

他补充说：“我认为我们必须克服‘抱最好的希望，把头埋在沙子里’的做法。”[qh]

Some researchers have theorized flu viruses that started in birds caused severe human pandemics.[qh]

一些研究人员提出理论，认为始于鸟类的流感病毒导致了严重的人类大流行。[qh]

For example, pandemics that took place in 1918 and 1957 quickly spread among animals and people.[qh]

例如，1918年和1957年发生的大流行病在动物和人类之间迅速传播。[qh]

Many experts think it would be unlikely the currently spreading virus will become a deadly, worldwide pandemic.[qh]

许多专家认为，目前正在传播的病毒不太可能成为一种致命的、全球性的大流行病。[qh]

But to prepare for that possibility, U.S. health officials are developing vaccines that might be needed.[qh]

但是为了为这种可能性做准备，美国卫生官员正在开发可能需要的疫苗。[qh]

At this time, they are not planning other measures.[qh]

此时，他们并未计划其他措施。[qh]

This is because the virus is not causing severe disease in humans and there is no strong evidence it is spreading from person to person.[qh]

这是因为该病毒并未在人类中引起严重疾病，也没有强有力的证据表明它在人与人之间传播。[qh]

The U.S. Department of Agriculture has said U.S. animal outbreaks have been reported at numerous dairy cow farms and among more than 1,000 groups of poultry.[qh]

美国农业部表示，美国已经有许多奶牛场和1000多群家禽报告了动物疫情。[qh]

At least four human infections have been reported among hundreds of thousands of people working at U.S. poultry and dairy farms.[qh]

在美国的家禽和奶牛养殖场工作的数十万人中，至少有四人被报告感染了禽流感。[qh]

Worldwide, doctors have so far identified 15 human infections caused by the current version.[qh]

在全球范围内，医生迄今已确认15例由当前版本引起的人类感染病例。[qh]

That count includes one death, a 38-year-old woman in southern China in 2022.[qh]

该数字包括2022年中国南方一名38岁女性的死亡病例。[qh]

But officials said most of the identified people had either no signs of disease or only mild ones.[qh]

但是官员们表示，大多数被识别出的人要么没有疾病迹象，要么只有轻微症状。[qh]

Some experts have wondered whether humans have built up some level of immunity after being infected by other virus forms or because of vaccination.[qh]

一些专家想知道，人类是否因为感染了其他病毒形式或接种疫苗而建立了一定程度的免疫力。[qh]

But a study involving human blood samples suggested there was little to no existing immunity to this version of the bird flu virus. [qh]

但是一项涉及人类血液样本的研究表明，对这种禽流感病毒的现有免疫力几乎为零。[qh]

I’m Bryan Lynn[qh]

我是布莱恩·林恩。[qh]