VOA健康报道2024--Scientists Study Why Bird Flu Kills Some Animals, Not Others

Scientists Study Why Bird Flu Kills Some Animals, Not Others

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

In recent years, bird flu is believed to have killed millions of wild and domestic birds worldwide. Other animals such as seals, cats, dogs and cows have also been infected.

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

Most of the human cases involved direct contact between people and infected birds. In cases of the virus spreading between humans, individuals involved were found to have had close and extended contact within households.

The currently spreading version of bird flu was first identified in 1959. But the illness did not start to cause concern among health officials until a bird flu outbreak hit Hong Kong in 1997. That outbreak caused severe sickness and deaths in some humans.

Scientists are still studying possible reasons the H5N1 virus has not heavily affected¹ human populations. But some researchers fear the situation may change.

Like other viruses, H5N1 has mutated over time. During the last few years, one particular bird flu version has been spreading quickly and widely.

Dr. Tom Frieden is a former director of the U.S. Centers for Disease Control and Prevention (CDC). He told The Associated Press about the ongoing² outbreaks, “There's a lot we don't understand.”

Frieden also heads the non-profit group Resolve to Save Lives. He added, “I think we have to get over the 'hope for the best and bury our head in the sand' approach."

Some researchers have theorized flu viruses that started in birds caused severe human pandemics. For example, pandemics that took place in 1918 and 1957 quickly spread among animals and people.

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

But to prepare for that possibility, U.S. health officials are developing vaccines³ that might be needed. At this time, they are not planning other measures. 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.

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 poultry⁴. At least four human infections have been reported among hundreds of thousands of people working at U.S. poultry and dairy farms.

Worldwide, doctors have so far identified 15 human infections caused by the current version. That count includes one death, a 38-year-old woman in southern China in 2022. But officials said most of the identified people had either no signs of disease or only mild ones.

Some experts have wondered whether humans have built up some level of immunity⁵ after being infected by other virus forms or because of vaccination⁶. But a study involving human blood samples suggested there was little to no existing immunity to this version of the bird flu virus.

Words in This Story

domestic – adj. relating to the home and family relationships

mutate – v. to cause a gene⁷ to change and create an unusual characteristic in a plant or animal

bury (one’s) head in the sand –idiom to avoid dealing⁸ with a difficult problem

approach – n. a way of doing something

dairy – adj. containing or made from milk

poultry – n. birds, as chickens or ducks, that are bred for their meat and eggs

immunity – n. bodily power to resist an infectious disease

1 affected   

adj.不自然的，假装的

参考例句：

• She showed an affected interest in our subject.她假装对我们的课题感到兴趣。
• His manners are affected.他的态度不自然。

2 ongoing   

adj.进行中的，前进的

参考例句：

• The problem is ongoing.这个问题尚未解决。
• The issues raised in the report relate directly to Age Concern's ongoing work in this area.报告中提出的问题与“关心老人”组织在这方面正在做的工作有直接的关系。

3 vaccines   

疫苗，痘苗( vaccine的名词复数 )

参考例句：

• His team are at the forefront of scientific research into vaccines. 他的小组处于疫苗科研的最前沿。
• The vaccines were kept cool in refrigerators. 疫苗放在冰箱中冷藏。

4 poultry   

n.家禽，禽肉

参考例句：

• There is not much poultry in the shops. 商店里禽肉不太多。
• What do you feed the poultry on? 你们用什么饲料喂养家禽?

5 immunity   

n.优惠；免除；豁免，豁免权

参考例句：

• The law gives public schools immunity from taxation.法律免除公立学校的纳税义务。
• He claims diplomatic immunity to avoid being arrested.他要求外交豁免以便避免被捕。

6 vaccination   

n.接种疫苗，种痘

参考例句：

• Vaccination is a preventive against smallpox.种痘是预防天花的方法。
• Doctors suggest getting a tetanus vaccination every ten years.医生建议每十年注射一次破伤风疫苗。

7 gene   

n.遗传因子，基因

参考例句：

• A single gene may have many effects.单一基因可能具有很多种效应。
• The targeting of gene therapy has been paid close attention.其中基因治疗的靶向性是值得密切关注的问题之一。

8 dealing   

n.经商方法，待人态度

参考例句：

• This store has an excellent reputation for fair dealing.该商店因买卖公道而享有极高的声誉。
• His fair dealing earned our confidence.他的诚实的行为获得我们的信任。