On March 26th, official website, Guangdong Provincial Center for Disease Control and Prevention announced that Zhongshan reported H3N8 cases 1 case. China Center for Disease Control and Prevention re-examined the case samples, and the results showed that H3N8 avian influenza virus nucleic acid was positive.
This is the third case of human infection with H3N8 avian influenza in China since 2022. According to the People's Daily Health Client News, according to Chinese scholars' research, in April 2022, there were cases of human infection with H3N8 subtype avian influenza in Henan Province and Hunan Province, and H3N8 subtype influenza virus infected a wide range of hosts. Previously isolated from birds, horses, dogs, pigs, seals and other animals, human infection is the first time.
According to official reports, both those infected before Henan and Hunan and the latest cases in Guangdong Province are accidental cases. At this stage, the risk of virus transmission is low. However, as early as February this year, the Director-General of the World Health Organization, Tedros Adhanom Ghebreyesus, publicly stated, "Although the risk of avian influenza infection faced by human beings is still low, we cannot assume that this situation will always exist, given that more and more poultry are infected."
How about three cases of H3N8 infection?
According to the report of Guangdong Provincial Center for Disease Control and Prevention, the patient infected with H3N8 avian influenza virus is a 56-year-old female with a basic history of multiple myeloma, a history of contact with live birds before the onset, and a history of wild bird activities around her home.
Unlike the human influenza virus that spreads in the epidemic season every year, avian influenza virus is difficult to infect humans because of the lack of corresponding binding receptors. But the problem is that with the spread of avian influenza virus among animals for many years, some strains have accumulated core mutations, thus achieving cross-species transmission from animals to people.
The same is true of H3N8 virus. H3N8 was first discovered in horses in 1963, causing equine influenza epidemic in the United States, also known as equine influenza virus. On 20 14, dogs in Florida, USA died of H3N8 virus infection. At that time, academic circles thought that H3N8 equine influenza had spread from horses to dogs, and had been able to spread from dogs to dogs.
At the same time, H3N8 is also a common avian influenza virus, which spreads in bird populations, especially among wild waterfowl all over the world. 20 1 1 year, Britain found that it had evolved the ability of cross-species transmission to seals-162 seals died of pneumonia caused by H3N8 virus infection.
On June 5438+065438+1October 10, in 2022, researchers in China published the details of the first case of human H3N8 infection in Nature News. The patient is a 4-year-old boy from Henan Province. After onset, the body temperature reached 4 1 degree, complicated with a series of complications such as pneumonia, abnormal liver function, kidney injury and coagulation dysfunction, and the condition was critical.
Retrospective epidemiological investigation showed that H3N8 positive results were detected in cats, dogs and chickens in children's living environment, and dogs infected with H3N8 also showed mild clinical symptoms. The researchers concluded that H3N8 may be the horizontal transmission between dogs, cats and people, whether through respiratory tract or gastrointestinal tract infection.
The second patient reported by China is a 5-year-old boy from Hunan. On September, 2022 1 1, the team of Professor Liu Jinhua from the College of Animal Medicine of China Agricultural University published an online study on this case in the journal The Lancet-Microbiology. The article shows that the child developed symptoms such as fever, sore throat and chills on May 9, 2022. The symptoms of infection were mild, and chest CT showed no signs of pneumonia. After that, it was treated with amoxicillin, clavulanic acid, infantile asthma and Qingre Granule.
In order to trace the source of infection, the researchers also conducted a detailed epidemiological investigation and found that there was no contact between the two children in Hunan Province and Henan Province. Children in Hunan have been to the fresh market near their place of residence six days before the onset of illness, where the varieties of live birds traded are chickens, ducks and pigeons.
The article points out that the two cases of H3N8 infection in Hunan Province and Henan Province are not adjacent geographically, and the time interval is short, indicating that "this new human avian influenza virus has a potential high risk of interspecific transmission."
Where does the new H3N8 come from?
Up to now, it has been confirmed that 1 1 subtype avian influenza virus can cause human infection. Relevant data show that the most "mainstream" strains are H7N9 1997 and 20 13 avian influenza virus strains.
1997, China reported the first case of human infection with H5N 1 avian influenza, with the onset of *** 18 people and 6 deaths; In 2003, two cases of human infection with H5N 1 avian influenza occurred in Hongkong, China, and 1 died. From 2003 to 20 15, 844 cases of human infection with H5N 1 avian influenza were reported in the world, among which 449 cases died, with a mortality rate of 53.2%. From March 20 13 to April 20 17, there were 6 cases of human infection with H7N9 avian influenza 14 16, and 559 people died.
Gao Fu, an academician of China Academy of Sciences and a virologist, once explained in a popular science book that the main cellular receptor of HA protein of avian influenza virus is α-2,3-galactoside sialic acid receptor, which only exists in the lower respiratory tract. Under normal circumstances, avian influenza virus is not easy to penetrate into the lower respiratory tract, and even if it arrives, it will be bound by tissue mucus and difficult to spread. The main cellular receptor of human influenza HA protein is α-2,6-galactoside sialic acid receptor, which exists in the upper respiratory tract.
Team Liu Jinhua retrospectively investigated the infection of H3N8 in three provincial farms in China from 202 10 to April 2022, and found that 15 H3N8 strains came from six provinces. It is worth noting that all 15 strains of virus were isolated from sick chickens. However, the previous monitoring data in Chinese mainland showed that H3Ny virus only spread dynamically in waterfowl and was never detected in chickens, indicating that the new H3N8 avian influenza virus in China has adapted to chickens and is pathogenic to chickens.
Subsequently, scientists compared the gene sequence of H3N8 virus infected by children in Henan and Hunan with the virus isolated from chickens mentioned above, and found that the gene sequence similarity of H (hemagglutinin) and N (neuraminidase) was over 98.7%.
Further analysis shows that before chickens, the key gene composition of the new virus can be independently traced back to domestic ducks, chickens and Russian or Japanese migratory birds in southern China.
According to a series of evidences, the paper concludes that human infection with H3N8 avian influenza virus comes directly from chickens, and evolved from H3 gene of Eurasian birds, N8 gene of North American birds and "triple recombination event" of internal gene of H9N2 avian influenza virus prevalent in China.
Will it cause a "human epidemic"?
Since the beginning of this year, there have been outbreaks of avian influenza in Europe, Japan, the United States, Argentina and other places. In late February, the Cambodian health department also reported that a girl aged1/kloc-0 died of H5N 1 avian influenza infection. When the health department checked the close contacts, it also found that her father was infected with the virus.
At present, it is not clear whether the two cases in Cambodia are "person-to-person" or whether the father and daughter have had contact with animals infected with H5N 1 virus respectively. However, it is generally recognized in the industry that the overall risk of cross-species transmission of avian influenza virus is not high, and there are even fewer cases of further interpersonal transmission.
However, virologist Chang Rongshan told Medical Science that it is alarming that once the virus spreads across species, human infection will lead to adaptive variation of the virus, which may make these viruses more likely to spread within species.
Not only birds, bears, foxes, raccoons, cougars and cats, but also related influenza viruses are widely spread in mammals. At the same time, different species may also become "mixed culture containers" of influenza strains from different sources, thus producing a brand-new strain that human beings are almost completely immune to.
"The ability of avian influenza virus to evolve and infect new species is random. Generally speaking, it will not be discovered until the infection of a species reaches a certain level. " Chang Rongshan told the "medical community" that when H3N8 was first discovered in the crowd, it meant that it had evolved the ability to infect humans.
In 2009, a new influenza A virus (H 1N 1) broke out all over the world. Evolutionary analysis shows that it contains gene fragments of three influenza viruses: avian influenza, swine influenza and human influenza. However, H7N9, which spread in China in 20 13, was recombined from avian influenza virus from chickens and ducks. A recent study published in the same health magazine also investigated the database of more than 70,000 animal influenza records from 1970 to 20 16, and considered that avian influenza may be the source of the next epidemic virus strain.
"The bird flu virus spread from one species to another and gradually became popular, once in history and once in human defense. But the virus will not' stop' and has been waiting for new opportunities. " Chang Rongshan said: "The scale is big and small."
Because the spread of avian influenza virus is random, Chang Rongshan believes that the most effective preventive measure is to avoid eating and contacting wild animals. "The more people are exposed to the source of infection, the greater the probability that the virus will break through and infect people, and there will be more opportunities to further acquire strong interpersonal skills."
The Guangdong Provincial Center for Disease Control and Prevention also issued a document to remind the public to avoid direct contact with live birds and dead birds in their daily lives. Once you find respiratory symptoms such as fever, cough and sore throat, you should wear a mask and seek medical attention as soon as possible. If they had contact with birds before getting sick, they should take the initiative to tell the doctor. All kinds of farmers' markets at all levels should abide by the Measures for the Administration of Poultry in Guangdong Province, and implement measures such as poultry management and sanitation in the market.
According to the above research of Liu Jinhua's team, industrialization, mixed feeding of different kinds of animals and live poultry market have created an ideal environment for influenza virus recombination and interspecific transmission. "Continued human infection with the new H3N8 virus may further drive the virus to gain a preference for binding with human receptors, which is a prerequisite for the occurrence of potential epidemics."
Therefore, the article finally wrote: "It is imperative to comprehensively monitor H3N8 avian influenza virus in poultry, especially broilers with signs of respiratory diseases. Controlling viruses prevalent in poultry can reduce the risk of human infection. "