Avian influenza situation

Highly pathogenic avian influenza (HPAI)

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Avian influenza is the abbreviation of avian influenza, which is an animal infectious disease caused by virus. It usually only infects birds and rarely infects pigs. Avian influenza virus is highly targeted at specific species, but in rare cases, it can cross the species barrier to infect people. Since 1997 discovered avian influenza in Hong Kong, the disease has attracted great attention from the World Health Organization. Since then, the disease has been sporadic outbreaks in Asia, but since June 5438+February, 2003, there have been serious outbreaks of avian influenza in many countries in East Asia, mainly in Vietnam, South Korea and Thailand, and many patients in Vietnam have died. Until mid-2005, the epidemic showed no signs of abating, but continued to spread. At present, there are cases in many countries as far away as Eastern Europe.

catalogue

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O 1. 1 Classification of pathogens

O 1.2 avian influenza infection

* 2 The source and spread of avian influenza

* 3 the impact of avian influenza

O 3. 1 Impact on economy

O 3.2 Impact on human beings

O 3.3 Ecological environment impact

* 4 Prevention and control of avian influenza

O 4. 1 source of infection

O 4.3 Susceptible population

O 4.4 Improper countermeasures

* 5 epidemic situation

* 6 references

* 7 See also.

* 8 external links

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Avian influenza biology

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Classification of pathogens

According to the antigenicity classification of nucleoprotein, avian influenza virus belongs to influenza A virus. Influenza A virus is divided into several subtypes according to the antigenicity of hemagglutinin and neuraminidase located on its envelope, and hemagglutinin (H) has 15 subtypes. There are 9 subtypes of neuraminidase (N). All these subtypes can infect birds, and the high pathogenicity in birds belongs to H5 and H7 subtypes. The typical fowl plague virus is H7N7, and H5N2 is the one that caused the pandemic in the eastern United States at 1983 and 1984. At present, people in Southeast Asia are infected with H5N 1 type. H5N 1 poison bead discovered in 1997 was identified as the source of influenza at that time. During 1999, H9N2 avian influenza occurred in Hong Kong, and H7N7 avian influenza occurred in the Netherlands in 2003.

According to the different toxicity in poultry population, avian influenza can be divided into low pathogenicity (LPAI) and high pathogenicity (HPAI). H5 and H7 subtype strains were found in both highly pathogenic and low pathogenic types, and H9 type was only found in low pathogenic type. Low pathogenic avian influenza can lead to mild respiratory symptoms, decreased food intake, decreased egg production and sporadic deaths in poultry. Highly pathogenic avian influenza is the most serious, with high morbidity and mortality, and all infected chickens often die.

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Avian influenza infection

Bird flu can spread to many kinds of animals, including birds, pigs, horses, seals, whales and humans. However, as asymptomatic carriers, wild birds spread them to more susceptible poultry. It is mainly transmitted in birds through respiratory tract and feces, and there is no evidence that the virus can survive in cooked meat. Viruses first infect the digestive tract of birds, they replicate in the epithelial cells of the small intestine, and finally spread with feces. The symptoms of bird flu infection in animals vary greatly, but the highly virulent type may die within a few days.

The symptoms of avian influenza are similar to those of other influenza, such as fever, cough, sore throat, muscle soreness and conjunctivitis. In severe cases, respiratory problems and pneumonia may be life-threatening. There are also some atypical symptoms. In one case, a boy infected with H5N 1 virus developed diarrhea.

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The source and spread of avian influenza

In the early period of 1900, avian influenza was first confirmed in Italy. In 960, more than 65,438+0,000 common terns died in South Africa. This is the first case of high mortality caused by avian influenza, belonging to H5N3 type.

According to the technical document H5N 1 issued by the Working Group on the Convention on Migratory Species of the United Nations Environment Programme, the source of subtype avian influenza comes from centralized poultry, and the extreme feeding environment leads to the variation of the virus. Human activities such as bird trade, vaccine abuse and transportation have also promoted the variation of avian influenza virus. Field research shows that the vast majority of wild birds suffering from avian influenza are species that have had close contact with poultry raised by human beings during migration, wintering and reproduction, while those wild birds, even waterfowl, which are far away from human society from beginning to end and maintain a high population density have not been reported yet.

Viruses from farms infect wild birds, especially waterfowl, making the virus spread with bird migration. The outbreak of avian influenza in East Asia from the end of 2003 to the beginning of 2004 is considered to verify the hypothesis that migratory birds spread viruses: the epidemic first appeared in South Korea, where migratory birds stopped, then passed through Hong Kong and finally arrived in Vietnam. Due to the relatively good sanitation environment in Hong Kong and previous experience in dealing with epidemic diseases, the disease did not cause a large-scale outbreak in the local area. Vietnam, with a relatively poor sanitation environment, not only kills birds, but also affects human beings. By June 5438+0, 2004, nearly 20 people had died. However, ornithologists pointed out that according to the laws of Siberia-East Asia-bird migration Passage, migratory birds basically completed their migration from north to south as early as the end of June165438+early February 65438. Previous radio positioning and tracking research in Hong Kong also showed that there were almost no migratory birds in the dead of winter. It is also observed that the wintering ground of most waterfowl is located in the north of 20 degrees north latitude, and only white-browed ducks and needle-tailed ducks will migrate to Vietnam, but their transit time is 65438+early February. It is generally believed by ornithologists that the outbreak of avian influenza at the end of 2003 did not overlap with the migration of migratory birds in time and space, so most ornithologists disagree with the statement that migratory birds spread the virus.

It's not just migratory birds that are accused of spreading bird flu virus. According to the communiqué of the Third Meeting of the Parties to the Agreement on the Protection of Non-Eurasian Migratory Waterbirds on 27 October 2005, besides migratory birds, there are other ways to carry and spread avian influenza virus, such as livestock transportation, poultry and caged birds transportation, activities related to this industry, legal or illegal bird trade and human trafficking.

In poultry, once ducks and geese are infected, their disease resistance is relatively high, and the chances of survival after illness are also high. However, chickens are very sensitive to influenza virus. Once infected, it not only spreads quickly, but also the infected chicken will die soon. In the past, farmers generally referred to this phenomenon as "chicken plague" and did not pay special attention to the reasons behind it or the pathogenesis. It was not until the case that bird flu spread from animals to people and died that people began to pay attention to bird flu. At present, the main means for people to deal with avian influenza is to collectively slaughter infected and possibly infected birds and then disinfect and bury them to avoid virus accumulation and further affect human beings.

In the bird flu epidemic in 2004 and 2005, some media also pointed out that the bird flu virus originated from wild birds, spread to farms and then passed on to humans. It is suggested to strengthen the monitoring of migratory birds' migration. A few activists even advocated culling migratory birds in addition to poultry, but this view was not recognized by ornithologists, and the proposal to cull migratory birds attracted opposition from environmental groups.

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Impact of avian influenza

The outbreak and epidemic of avian influenza will have many effects.

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Impact on the economy

Countries and regions where avian influenza broke out will cull poultry on a large scale near the epidemic spot for epidemic prevention reasons, which will have a serious impact on the aquaculture industry. The bird flu epidemic will also affect consumer confidence and hit the catering industry. Considering epidemic prevention, other countries and regions will suspend the import of poultry and products from epidemic areas, which will have an impact on the economy.

The governments of some countries and regions will block and conceal the occurrence of bird flu in their own countries only considering the huge impact of bird flu epidemic on the economy. However, this concealment of the epidemic situation often leads to poor epidemic prevention and further expansion of the epidemic situation. At the end of 2004, the Prime Minister of Thailand publicly apologized to the world for his government's concealment of the bird flu epidemic.

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Influence on human beings

Although the epidemic of avian influenza in June 5-38+February 2004 spread throughout many countries, only human cases were reported in Vietnam and Thailand. * * * 32 people were diagnosed in the laboratory and 22 people died, with a mortality rate as high as 70%. Although there are very few cases, in view of the serious epidemic situation of Spanish influenza in 19 18, whether avian influenza is zoonotic has always attracted much attention. At present, H5N 1 influenza virus has not been recombined with human influenza virus, and there is not enough evidence to prove human-to-human transmission, which is unlikely to cause mass death.

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Impact on the ecological environment

Avian influenza virus can infect wild birds, especially waterfowl. Many waterfowl will flock in groups during migration, wintering and during the period, with high population density, and the virus is easy to spread, causing serious harm. According to the report of the United Nations Environment Programme, 36 kinds of precious wild birds, including the spotted goose, the small white goose, the oriental stork and the white crane, are threatened by avian influenza. It is estimated that in the summer of 2005, more than110 wild geese died in the world. Because bird flu virus can spread among birds, and some birds have relatively concentrated habitats, the impact of bird flu epidemic on some birds may be disastrous.

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Prevention and control of avian influenza

To control infectious diseases, we should start with three links: the source of infection, the route of transmission and the susceptible population.

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source of infection

To prevent avian influenza, we must first start from the source of infection. Relevant reports pointed out that extreme poultry breeding environment is an important factor to promote the mutation of avian influenza virus, so improving poultry breeding environment and reducing the breeding density of farms are the fundamental means to prevent the mutation of avian influenza virus and the outbreak of epidemic diseases in the long run. In addition, keeping different kinds of poultry separately can also help to control the spread of epidemic diseases: keeping ducks, geese and chickens separately can prevent chickens from being infected with ducks and geese and dying in large numbers.

At present, vaccination for poultry has been proved to be the fastest and most effective way to control avian influenza. However, some experts in Hong Kong said that there is a certain risk in the current method of vaccinating all poultry in China mainland farms, that is, all poultry are vaccinated, so that all poultry have disease resistance. In this way, once bird flu breaks out again, all birds have the ability to resist disease, so farmers can't find it early and send an early warning to the relevant departments. At present, the practice in Hong Kong is to require all farms to keep a small number of birds that have not been vaccinated. In this way, once the bird flu comes again, these unvaccinated birds can play an early warning role and remind other farms to pay attention to the virus coming again. In addition, according to the work report of the United Nations Environment Programme, vaccine abuse is also an important factor inducing the variation of influenza virus, so over-injection of vaccine is not worth advocating.

The guiding principles of poultry culling issued by the World Organization for Animal Health on June 29th, 2005 mainly include the following aspects: poultry culling should be carried out under the guidance of professional veterinary experts, and personnel's biological protection should ensure animal welfare.

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Transmission routing

Migratory birds are important spreaders of avian influenza virus, but it is impossible to slaughter all infected migratory birds. The culling of migratory birds will disperse the originally gathered birds, making the spread of the virus more difficult to control. Therefore, isolating poultry from migratory birds and avoiding cross-infection are effective means to control the spread of avian influenza. In China, many farms hang giant nets in poultry farms to prevent virus-carrying migratory birds from infecting poultry. In addition, some European countries require farms to move birds indoors in order to cut off the contact between poultry and wild birds from the transmission route. Although moving poultry indoors will reduce their activity space, thus affecting the texture of poultry meat, it is also less than the loss caused by the need to eliminate all birds because of bird diseases.

In addition to bird migration, the global bird trade is also an important route for the spread of avian influenza virus. Legal bird fairs carry out strict animal epidemic prevention inspection in accordance with relevant laws and regulations, and the probability of spreading diseases is relatively small. The illegal bird trade, especially the smuggling of wild birds, is not within the monitoring scope of animal epidemic prevention. Capturing, selling, selling, eating and releasing wild birds will not only cause the virus to spread across regions, but also cause the virus to spread among birds due to the close contact between operators and wild birds. Therefore, strict monitoring of legal and illegal bird trade is also an important link to prevent and control the spread of avian influenza.

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susceptible population

On the human side, we should always keep farms and poultry farms clean and hygienic to avoid the accumulation of viruses. In addition, according to Dr. Jeremy Faller's clinical experience in Hanoi, Vietnam, when people with active autoimmune systems are exposed to the virus, the virus will stimulate the immune system and cause more damage to lung tissue. Therefore, if individuals are known to be sensitive to pollution, they should be extra careful.

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Improper countermeasures

According to the technical document published by the Working Group on the Convention on Migratory Species of the United Nations Environment Programme, the idea of preventing and controlling avian influenza from the source of infection and transmission route is correct, but under the global avian influenza panic, some improper countermeasures have emerged. In some zoos in China, in order to separate wild birds from birds kept in parks, managers turn on searchlights all night to drive away wild crows; In Macao, the government lists sparrows as harmful birds and needs to drive them away; In addition, in some places, any activities related to birds are completely banned, including live poultry trading, wildlife rescue and bird field observation. In fact, birds common in many cities, including crows and sparrows, are resident birds and will not migrate long distances, so the probability of spreading avian influenza is extremely low. However, general research and proper contact with birds can not significantly increase the probability of contact with avian influenza. Excessive reaction to avian influenza will cause social panic and create artificial obstacles for bird research and normal prevention and control of avian influenza.

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epidemic

* In the winter of 2004, H5N 1 subtype avian influenza occurred in East Asia.

* In June, 2005, 5438+ 10, cases of H5N 1 avian influenza infection were reported in East Asia, Southeast Asia and Europe.

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reference data

* RTHK TV programs-collected tons: July 24th, 2005 and1October 23rd 10.

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see

* Influenza virus

* Infectious diseases

* H5N 1 Influenza