Research shows that there have been three world influenza pandemics in the world, all of which originated in China. Therefore, whether China can cope with bird flu is also of great significance to the world.

But so far, where the bird flu virus came from and where it is going is still unknown to human beings.

Since the discovery of human influenza virus, there have been three world influenza pandemics, all of which originated in China. Avian H5N 1 and H9N2 viruses can directly infect humans, which were first reported in Hong Kong and Guangdong Province in 1997 and 1998 respectively. Therefore, China is considered as the frequent place of new subtypes of human influenza virus, and the exact reason is not clear.

In September, 2005, Guo Yuanji, a researcher at China Center for Disease Control and Prevention, wrote an article in China Journal of Experimental and Clinical Virology.

China, with its vast territory and high population density, is the main distribution center for migratory birds. As a big agricultural country, China currently raises more than 654.38+0.3 billion poultry, and waterfowl farming accounts for one third of the world, and it is mainly free-range and domestic. Therefore, if the origin of influenza epidemic strains is closely related to avian influenza virus, it is logical that most of them are found in China.

In this situation, whether China can prevent and control the further development of avian influenza is of great significance not only to China, but also to the world.

Where did the virus come from and where did it go?

Dingdang Town, Longan City, Guangxi Zhuang Autonomous Region is the starting point for Chinese mainland to be infected with highly pathogenic avian influenza virus H5N 1. On June 27th, 2004, at 65438, the National Avian Influenza Reference Laboratory finally determined that the poultry deaths here were caused by H5N 1 highly pathogenic avian influenza virus.

Before the incident, this epidemic situation was reported in neighboring countries: Korea 65438+February 2003, Vietnam 65438+20041October 5, Japan 65438+1October1,followed by Thailand, Cambodia and Laos. Looking around, Chinese mainland has been surrounded by bird flu. Just a few days later, the virus "landed" in this small town 200 kilometers away from the Sino-Vietnamese border.

Strangely, Dingdang Town was originally an isolated town, and no one traveled between China and Vietnam before the incident. So where did the virus come from?

On the day when the epidemic situation was confirmed in Dingdang Town, a chicken farmer in a forest farm in Hubei Province and a duck farmer in Hunan Province also found the death of birds. Three days later, the test results were announced, and H5N 1 was indeed infected. Then Jiangxi, Anhui, Yunnan, Guangdong, then Shaanxi, Gansu, Zhejiang, and even Xinjiang and Tibet were not spared. In just one month, 49 epidemic cases have been confirmed in 6 provinces/KLOC-0.

The epidemic situation is rapid, from Xinjiang in the west to Shanghai in the east, from Jilin in the north to Yunnan in the south, and the epidemic situation is one after another in such a large range, with no regularity. Efforts to trace the source of the epidemic have been going on, but there has been no result.

Dingdang Town first found the infected duck farmers, and then found a duck farm from the duck farmers, only to find that the duck farm was intact and the ducks sold in other places were also intact.

All kinds of doubts can't be explained, and the focus begins to gather on free-flying birds.

According to the statistics of biologists, there are more than 9,000 species of birds in the world, and there are about 1200 species in China, including more than 540 species of migratory birds. These birds are widely distributed, almost everywhere in China. According to the characteristics of the epidemic situation, such as large span and rapid spread, migratory birds traveling back and forth between breeding grounds and wintering areas in spring and autumn have become the key suspects of the epidemic situation.

But not all avian influenza viruses are pathogenic. Among the subtypes 15 H and 9 N of avian influenza virus, only H5 and H7 subtypes are related to the high pathogenicity of poultry. The isolation rate of these two virus types in wild birds is the lowest.

In April, 2004, Feng Li, Ding Changqing, Lei Fumin and other experts from the Institute of Zoology, Chinese Academy of Sciences jointly published the article "The Relationship between Wild Birds and Avian Influenza", which showed that the avian influenza virus isolated from wild birds was basically low in pathogenicity and would not spread to birds immediately and cause death. No cases of bird flu have been found in wild birds, and no one has been infected with bird flu through wild birds.

If so, how did the highly pathogenic avian influenza virus spread in more than ten provinces in East Asia, Southeast Asia and Chinese mainland?

Although there were no cases of bird flu outbreaks among wild birds at that time, Feng Li and others affirmed in their articles that bird flu virus could be transmitted to poultry through wild birds, especially waterfowl such as ducks and geese.

The route of infection may be the contact between wild ducks and domestic ducks, domestic ducks and domestic chickens, or it may be because bird flu can survive in feces for a long time, and people or dogs walking in the field, even mice and other animals come into contact with the feces of polluted wild ducks or geese, bringing the virus into farmers. This will make it possible for low pathogenic virus to mutate into high pathogenic virus.

Is it true that the virus in wild birds is transmitted to poultry and then mutated to lead to a highly pathogenic avian influenza epidemic?

More seriously, the avian influenza virus is no longer confined to the spread between birds, but has appeared the phenomenon of human infection. In Vietnam, only from February 28th, 2003 to February 27th, 2004, 297 suspected cases of human avian influenza were reported, including 22 confirmed cases.

It was also at this time that the Ministry of Health of China sent a medical treatment investigation team led by the Medical Department to Hanoi. Professor Xu from the Department of Infectious Diseases of the First Hospital of Peking University participated in the rescue inspection as a member of the expert group.

He recalled to reporters that there were people infected in Vietnam, when bird flu broke out in China, and Vietnam and China were close neighbors. In order to nip in the bud, the Ministry of Health decided to send an expert group to Vietnam to learn about the situation. After investigation by the expert group, it was found that all the confirmed people were infected with H5N 1 subtype influenza virus and had a history of close contact with poultry. Although there is no human transmission, Xu is still worried that the virus will mutate. According to the characteristics of avian influenza virus, it first spreads among birds, and then spreads from birds to people. Once the virus adapts to the human environment, it is inevitable that there will be infection between people.

"Criminal evidence" of flight

After an uneasy February, the bird flu epidemic in Chinese mainland gradually subsided. In less than two months, the total number of sick birds was 6.5438+0.5 million, 6.5438+0.3 million died and 9.05 million were culled.

What is even more annoying is that it is not clear where these viruses come from.

The turning point occurred on May 4, 2005, when the managers of Bird Island Management Station of Qinghai Lake Nature Reserve Administration visited Bird Island, they suddenly found an abnormal situation of a spotted goose. Spotted goose then died. On May 18, H5N 1 subtype avian influenza virus was isolated from dead birds by National Avian Influenza Reference Laboratory. During this period, cormorants, brown-headed gulls, fish gulls, spotted geese and so on 1000 migratory birds died near Qinghai Lake.

This is obviously an amazing news. This is not only because it is the first time that such a large area of migratory birds broke out in the world in previous studies, but more importantly, these migratory birds carrying highly pathogenic avian influenza virus may spread the virus during their migration, which is the focus of people's attention.

As an important transit point for migratory birds in the world, Qinghai Lake has a very prominent position, with more than 400,000 spotted geese, brown-headed gulls and cormorants. If it is confirmed that migratory birds can spread avian influenza virus, it may mean a global crisis.

Lu Taichun, a researcher at the Institute of Zoology, Chinese Academy of Sciences, said in an interview that an investigation team composed of several departments has gone to all parts of the country to investigate migratory birds, including Shandong, Liaoning, Heilongjiang, Yunnan and some waters where migratory birds live.

Where is the next stop for migratory birds?

Doubts are gradually tilting in the direction of migratory birds spreading the virus. Shortly after the discovery of dead migratory birds in Qinghai Lake, outbreaks occurred in Mongolia and Kazakhstan.

In August, avian influenza entered Russia, and 5438+ 10 reappeared in Hohhot, Inner Mongolia, China. Just when people were worried that bird flu would threaten Beijing, Hebei and other neighboring provinces and cities, it suddenly appeared in Anhui and Hunan provinces in central China a few days later. After being identified as H5N 1 virus, Xinhua News Agency said that the epidemic situation of highly pathogenic avian influenza in Xiangtan County, Hunan Province was "initially suspected to be caused by waterfowl carrying the virus".

June 5438+ 10 is the season for migratory birds to migrate from north to south in search of wintering grounds. Avian influenza develops from south to north in spring and from north to south in autumn. All this coincides with the migration route of migratory birds, and a clearly identifiable infection chain seems to be presented to everyone.

However, birdlife international's report is quite cautious about this. One of the evidences is that when bird flu broke out in Asia in February 2004, it was not the time for migratory birds to migrate, but they should have stayed in the wintering place in Southeast Asia.

It is Lu Jun, an associate researcher of China Bird Environmental Records Center, who feels that the transmission route of avian influenza is not completely consistent with the migration route of migratory birds. He said that in early May, migratory birds from Southeast Asia and India had migrated to Qinghai Lake. If they are infected with the virus at the beginning, it is difficult to lurk for so long before the outbreak. "It remains to be confirmed which part of the virus is infected."

On June 365438+1October 3 1 day, 2005, officials of the State Forestry Administration also said that no reports of bird flu infection have been found so far, and the State Forestry Administration has also started the monitoring point of 1 18 on the main migratory routes of migratory birds to prevent abnormal situations of migratory birds at any time.

Chu Guo Zhong, director of China Bird Environmental Recording Center, who is conducting field monitoring in Hubei and Hunan, also answered the reporter's question in one sentence: "Everything is normal."

He said that at present, the research on migratory birds in China lags far behind that in developed countries, and even the migration routes of various birds have not been established, so it is still too early to draw any conclusions on the transmission route of the virus before there is definite evidence.