為什么有些人的新冠感染癥狀會長期存在？

Nearly one in five people who have had COVID-19 in the United States continue to suffer from symptoms of long COVID. But why some people recover completely while others remain sick has been a mystery. Now research has provided some interesting clues.

A new study shows that bits of virus that survive in the gut（腸道） cause chronic inflammation， which reduces production of serotonin — a molecule critical for communication between nerve cells in the gut and brain. The authors of the new article suggest that waste of serotonin disrupts gut-to-brain communication， which can cause long-term neurological（神經(jīng)系統(tǒng)的） symptoms such as “brain fog” and impaired memory.

The brain and the gut talk to each other. In fact， the gastrointestinal（胃腸的） nervous system with its own 500 million neurons is so large， it is sometimes called the “second brain.”

About 95 percent of the serotonin is produced in the gut， although the brain makes its own supply. Microbes that live in our gut also produce chemical neurotransmitters， including serotonin. While serotonin produced in the gut does not directly reach the brain， it can influence the brain via neuronal circuits through vagus nerve.

“That’s why when you’re feeling stressed， you can get abdominal pain or diarrhea，” says Kenji Hashimoto， a neuroscientist at Chiba University in Japan.

This may explain how “l(fā)ong COVID might be linked through a pathway that originates in the gut and leads to serotonin reduction，” says Christoph Thaiss， a microbiologist at the University of Pennsylvania， who led the study.

“These are very important findings that help explain why serotonin levels remain low in certain long COVID patients following SARS-CoV-2 infection，” says Liam O’Mahony， an immunologist at APC Microbiome Ireland， University College Cork， who was not involved in Thaiss’ work.

（材料來自National Geographic網(wǎng)站，有刪改）

1. According to the text， what makes some people suffer from long COVID？

A. The production of serotonin in the gut.

B. The production of serotonin in the brain.

C. The reduction of serotonin in the gut.

D. The reduction of serotonin in the brain.

2. What does the underlined word “impaired” in Paragraph 2 refer to？

A. Self-healed. B. Damaged.

C. Renewed. D. Strengthened.

3. According to Hashimoto， you can suffer from  under pressure.

A. abnormal pain B. cell loss

C. toothache D. diarrhea

4. What’s the attitude of experts mentioned in the text toward the new study？

A. Supportive. B. Disapproved.

C. Indifferent. D. Neutral.

1. C。（剩余467字）