What Are the Different Types of Bird Flu Viruses?

Avian influenza virus (AIV) is an influenza A virus. Influenza viruses belong to the orthomyxoviridae family of RNA viruses, which are divided into three types: A, B, and C. Among them, influenza A virus is more common in birds, and some types A can also infect various mammals and humans such as pigs, horses, seals and whales; influenza B and C viruses are found in seals and swine infections, respectively.

It is avian influenza, a type of infectious disease caused by influenza A virus in birds, from respiratory system to severe systemic sepsis. Avian influenza is easy to spread among birds. In the past, it was called "chicken fever" in the folk. Bird flu broke out in 1994, 1997, 1999, and 2003 in Australia, Italy, Hong Kong, China, and the Netherlands, respectively. In 2005, it mainly occurred in Southeast Asia and Europe.

Chinese Medicine Name: bird flu virus
English name: AIV
Disease site: Respiratory tract

Multiple groups: Children, elderly
Contagious: Contagious
way for spreading: Breathe

Bird flu virus prevention

Bird flu usually occurs in spring and winter and is generally not transmitted from person to person. To prevent bird flu induction, note the following: a. Wash your hands frequently and keep away from the secretions of poultry. If you have contacted poultry, birds or poultry, bird droppings, please clean your hands thoroughly with disinfectant and water to avoid traveling to the affected area; b. Develop good personal hygiene habits, cover your mouth with toilet paper or hands when coughing, and strengthen indoor air circulation. Open the window 1 to 2 times a day for half an hour. Have sufficient sleep and rest, a balanced diet, and pay attention to taking more food. Add some foods that are rich in vitamin C and other immunity; c. Poultry should be cooked and thoroughly cooked. When eating eggs, the shells should be washed with running water first. The cooking should be done with sufficient heating.

Avian Influenza Virus Morphology

Avian influenza virus components

Influenza A virus presents

bird flu virus Polymorphism, in which the spherical diameter of 80 ~ 120nm, there is a capsule. The genome is segmented, single-stranded negative-strand RNA. Based on the antigenicity of the outer membrane hemagglutinin (H) / and neuraminidase (N) proteins, it can be divided into 16 H subtypes (H1 to H16) and 9 N subtypes (N1 to N9). The main subtypes of avian influenza virus that infect humans are H5N1, H9N2, and H7N7. Among them, patients infected with H5N1 are seriously ill and have a high mortality rate.

Avian influenza virus performance

Studies have shown that the original low-pathogenic avian influenza virus strains (H5N2, H7N7, H9N2) can be rapidly mutated from 6 to 9 months to become highly pathogenic strains (H5N1).

Avian influenza virus epidemiology

Bird flu virus source

Avian influenza virus can

Avian influenza virus attacks healthy cells Breed in the digestive tract of waterfowl.

It is mainly poultry infected with avian influenza or avian influenza virus, and wild birds or pigs can also be the source of infection. Many poultry can be infected with the virus: turkeys, chickens, pigeons, guinea fowls, quail, parrots and other land birds can be infected, but turkeys and chickens are the most susceptible, with high morbidity and mortality; ducks and Waterfowl, such as geese, are also susceptible to infection, can be poisonous or recessive, and sometimes die in large numbers. Chickens and turkeys of all ages can be infected and die, and the mortality of water birds such as ducklings and goose is higher.

In addition to wild birds, such as swans, terns, wild ducks, coast birds, and sea birds, influenza viruses have been isolated from a variety of birds; bird myna, pheasant, sparrow, crow, jackdaw, pigeon, rock wren, Swallows, herons, Canada geese and muscovy ducks. According to foreign reports, 88 species of birds carrying the bird flu virus have been found, and rodents cannot naturally become infected with the influenza virus.

Different breeds of poultry have different rates of bird flu infection, but it has not been found that the occurrence of highly pathogenic avian influenza is related to the sex of the birds, and the highly pathogenic avian influenza virus can also be transmitted through eggs.

The transmission of highly pathogenic bird flow between flocks mainly depends on horizontal transmission, such as air, feces, feed, and drinking water, and there is little evidence of vertical transmission. However, experiments have shown that the eggs of experimentally infected chickens contain influenza virus, so the possibility of vertical transmission cannot be completely ruled out. Therefore, the eggs of contaminated flocks cannot be used for hatching.

The virus can be excreted with the respiratory tract, eye and nose secretions, and feces of sick birds, and birds can be infected through the digestive and respiratory tracts. Any object contaminated with sick bird feces and secretions, such as feed, poultry houses, cages, feeding and management equipment, drinking water, air, transportation vehicles, people, insects, etc., can spread the virus.

Avian influenza virus transmission

It is mainly transmitted through the respiratory tract. It is infected through close contact with infected birds and their secretions, excreta, virus-contaminated water, and direct contact with the virus strain. The feces of infected waterfowl contain high concentrations of the virus and the flu virus is transmitted from the fecal-oral route through contaminated water sources. No hidden infection has been found in humans, and there is no definitive evidence of human-to-human transmission.

Avian influenza virus susceptible population

It is generally considered susceptible at any age, but children under the age of 12 have a higher incidence and are more severe. People in close contact with undiagnosed or dead poultry or infected, suspected to be infected with avian influenza are at high risk.

Avian influenza virus epidemic characteristics

Avian influenza was distributed worldwide, with outbreaks in Australia, Italy, Hong Kong, China and the Netherlands in 1994, 1997, 1999, and 2003, respectively. In 2005, the outbreaks mainly occurred in Southeast Asia and Europe. With the exception of bird flu, which occurs mainly in winter and spring, there is no other regular pattern. The spread of the highly pathogenic avian influenza epidemic has drawn worldwide attention. Chinese weather experts' analysis of the climatic characteristics of the epidemic area shows that bird flu is "not happy" with hot and sunny weather.

The World Health Organization (WHO) believes that feces of sick birds are the main channel of transmission, and some experts believe that migration of migratory birds is also one of the channels of transmission.

Weather and climatic conditions are an important factor in the natural environment, and their changes or abnormalities usually play a role in the occurrence, exacerbation or alleviation of some diseases. Experts believe that the bird flu virus likes cold and humid, and the ultraviolet rays in the sun have a certain killing effect on the virus. In the late winter and early spring, frequent cold air activities and high and low temperatures will be detrimental to the control and prevention of bird flu. In addition, with the warming of the temperature, migratory birds will migrate northward, and the range of viruses transmitted by migratory birds will be expanded, which will also be detrimental to controlling the occurrence of bird flu.

The WHO believes that the H5N1 avian influenza virus strain in the feces of sick chickens will spread in the air and be carried away by the wind to spread bird flu. Judging from the hours of sunshine, analysis materials show that areas with less sunshine are prone to bird flu. This is in line with the point made by agricultural experts that the bird flu virus can only survive for 24 to 28 hours in the sun, and is generally epidemic in winter and spring. It is basically flat from May to October.

The highly pathogenic avian influenza virus is mainly transmitted through the air. With the help of hemagglutinin (H) on the surface of the virus, it binds to corresponding receptors on the surface of respiratory epithelial cells and adsorbs on host respiratory epithelial cells. With the help of the neuraminidase (N) on the surface of the virus, it acts on the receptor of the nucleoprotein, so that the virus binds to the nucleoprotein of the epithelial cells, forms an RNA-soluble antigen in the nucleus, exudates around the cytoplasm, and replicates the progeny. The virus, through the action of neuraminic acid, excrets epithelial cells in a budding manner. The cycle of a replication process is 4-6 hours. The discharged virus spreads to nearby cells and produces an inflammatory response. Clinically, systemic toxemia-like reactions such as fever, muscle pain and leukopenia occur.

The virus mainly invades the epithelial cells of the respiratory mucosa, causing epithelial cell proliferation, necrosis, local congestion of the mucosa, edema, and superficial ulcers. After 4 to 5 days, the basal cell layer lesions can extend to the bronchi, bronchioles, alveoli, and tissues around the bronchi, causing mucosal edema, congestion, and lymphocyte infiltration, accompanied by microvascular embolism, necrosis, small aneurysm formation, and bleeding. Systemic toxemia-like reaction. A few severe progressive pneumonia, in addition to bronchiolar inflammation changes, may include alveolar wall congestion and edema, fibrin exudation, monocyte infiltration and transparent membrane formation, and pulmonary hemorrhage, which cause many complications.

The highly pathogenic avian influenza virus has strong virulence, and the infectious allergies (type IV allergies) caused are serious diseases such as progressive pneumonia, acute respiratory distress syndrome (ARDS), and multiple organ dysfunction syndrome (MODS). The root cause of complications.

Avian influenza virus and human relationship

Human research and control of bird flu has a history of more than 100 years. Gene fragments, unless avian influenza virus and human influenza virus are genetically recombined, it is difficult to invade humans and cause human-to-human transmission. Human bird flu can only be caused by contact with sick birds. Humans are less likely to contract the virus.

Avian influenza virus is an influenza A virus. Influenza viruses belong to the orthomyxoviridae family of RNA viruses, which are divided into three types: A, B, and C.

Avian influenza virus pathological changes

Avian influenza virus simple influenza

Only the catarrhal inflammation of the upper respiratory tract was observed. Congestion, edema, and lymphocyte infiltration were seen in the mucosa. Fibroepithelial cells degenerate, necrotize, and fall off.

Avian influenza virus pneumonia influenza

The lungs are dark red like edema. There are bloody secretions and mucosal congestion in the trachea and bronchi, their ciliated epithelial cells are necrotic and shed, submucosal focal bleeding, edema and leukocyte infiltration, fibrin exudate in the alveoli, including neutrophils and lymphocytes. Alveolar hemorrhage in the middle lobe of the lung, there may be a transparent membrane in the alveoli, the lung tissue is easy to isolate influenza virus.

Severe complications of avian influenza virus

The main pathological change was consolidation of the lungs. Pulmonary interstitial edema and reduced interstitial negative pressure increase the tendency of small airway occlusion, resulting in atelectasis; alveolar membrane surface active substances are reduced, alveoli are also occluded; combined with pulmonary congestion, lung capacity is reduced and lung compliance Sexual decline, leading to serious complications such as acute respiratory syndrome.

Avian influenza virus characteristics

Avian influenza virus pathogenicity

Generally speaking, bird flu virus and human flu virus

Prototype h5n1 avian influenza virus There are receptor-specific differences, and avian influenza viruses are not easily infected by humans. Individual bird flu viruses that cause human infections may be mutated viruses. The possibility of mutation is that two or more viruses enter the same cell for recombination. For example, pigs can be infected with both human influenza virus and avian influenza virus. Each virus has 8 gene fragments. In theory, it can form 256 new recombinant viruses; second, the viral gene locus was affected by some factors. In April 1983, the outbreak of H5N2 virus in chickens and turkeys caused by the outbreak in Pennsylvania in the United States was not timely Effective control. By October of the same year, the same H5N2 strain suddenly changed from low pathogenicity to high pathogenicity, causing a large number of bird deaths.

Avian influenza virus adaptability

Avian influenza virus is sensitive to organic solvents such as ether, chloroform, and acetone. Common disinfectants can easily inactivate them, such as oxidants, dilute acids, sodium lauryl sulfate, halogen compounds (such as bleach and iodine) can quickly destroy its infectivity.

Avian influenza virus is more sensitive to heat. It can be inactivated by heating at 65 ° C for 30 minutes or boiling (100 ° C) for more than 2 minutes. The virus can survive for 1 week in feces and 1 month in water. It also has viability under the condition of pH 4.1. The virus has a strong resistance to low temperature and can maintain vitality for more than 1 year under the protection of glycerol.

The virus can be inactivated in direct sunlight for 40 to 48 hours. If it is directly irradiated with ultraviolet rays, it can quickly destroy its infectivity.

Avian influenza virus molecular characteristics

Molecular Structure

Crystal structure of avian influenza virus polymerase

The widespread spread of the outbreak caused by the H5N1 avian influenza virus poses a major global threat to human health. Due to the constant mutation of the virus, the development of new anti-influenza drugs has become a very urgent and important issue in various countries. Among them, revealing the three-dimensional structure of proteins closely related to influenza virus is not only of great scientific significance for revealing the mechanism of influenza virus replication, but also of great value for the development of anti-influenza virus drugs. The research group led by researcher Liu Yingfang of the Institute of Biophysics of the Chinese Academy of Sciences and the research group led by Rao Zihe made academic breakthroughs in this field. They are the first in the world to reveal the key component of the influenza virus polymerase PA subunit and PB1 peptide complex. The fine three-dimensional structure of the volume.

Influenza A virus polymerase is composed of three proteins-PA, PB1 and PB2, which are key to transcription and replication. Two groups reported the crystal structure of the C-terminal region of avian influenza virus H5N1 PA in a complex formed with the PA-binding region of PB1. This structural study may be useful for the design of new antiviral drugs.

The influenza virus genome contains eight RNA fragments and is known to encode 11 viral proteins. Among them, the polymerase complex composed of 23 subunits of PA, PB1 and PB is a key component responsible for viral genome RNA replication and viral mRNA transcription. At the same time, due to its high conservation and low mutation rate, it has become an anti-influenza virus drug design. Important target. Studies over the years have suggested that PB1 is the catalytic subunit of viral RNA polymerase and is responsible for viral RNA replication and transcription; PB2 is responsible for capturing the CAP cap structure of host mRNA for viral mRNA transcription in a manner known as "Snatch" . The PA subunit not only participates in the viral replication process, but also participates in various viral activities such as viral RNA transcription, endonuclease activity, protease activity, and viral particle assembly. Therefore, it appears particularly in the entire polymerase complex research. important. After screening crystal growth conditions, optimizing crystal quality, collecting high-resolution data, phase analysis, interpretation of electron density maps, and structural modification, they used a new idea to analyze the 2.9 angstroms of the PA-PB1 amino-terminal peptide protein complex. Resolution crystal structure. This structure clearly shows the interaction pattern of PA and PB1 polypeptides. It is found that the amino acid residues at this interaction site are highly conserved in influenza viruses, which provides an ideal for the research of broad-spectrum anti-influenza (including human and bird flu) drugs. Target protein. At the same time, based on the structure of the complex and some known protein mutant research results, it is speculated that the role of PA subunits in polymerases provides a molecular basis for further functional research. Revealing the structure of this complex is of great significance for revealing the mechanism of influenza virus polymerase action and for designing drugs for influenza viruses.

Polymerase

It is a collective name for a class of enzymes specialized in biocatalytic synthesis of DNA and RNA.

Can be divided into the following groups: (1) DNA-dependent DNA polymerase; (2) RNA-dependent DNA polymerase; (3) DNA-dependent RNA polymerase; (4) RNA-dependent RNA polymerase. The first two are DNA polymerases, which extend the DNA replication strand in template order. For example, in prokaryotes, only three have been found in E. coli (referred to as P01, P01, P01, etc.); DNA polymerase can only be based on primers, that is, 3 of DNA or RNA primers. -OH extension, the synthesis direction of this DNA is recorded as 5 3 . In other words, a DNA polymerase-catalyzed reaction requires Mg2 +, template DNA, and primers in addition to the substrate (NTP). So far, no cell has been found to initiate DNA synthesis from monomers. Similarly, the above (3) and (4) are the most important RNA synthetases that catalyze RNA biosynthesis reactions. They use four ribonucleoside triphosphates (NTP) as substrates and require DNA templates and Mn2 + and Mg2 +. In the presence, the 3-OH of the previous nucleotide and the 5-P of the next nucleotide are polymerized to form a 3 , 5-phosphodiester bond, and the direction of the nascent strand is also 5 3 . RNA polymerase is also abundant in cells of prokaryotes and eukaryotes. For example, E. coli RNA polymerase has a molecular weight of 4.8 × 105 and consists of five polypeptide chains, which are named , , , , and . The whole enzyme can be expressed by 2. Eukaryotic RNA polymerase molecules are larger than 5 × 105 and consist of 10-12 subunits of varying sizes. In addition to being an indispensable component of life activities in nature, polymerases are mostly used in the laboratory as one of the enzymes for life science research.

H5N1 Avian influenza virus new H5N1

The United Nations Food and Agriculture Organization pointed out on the 29th that H5N1, a highly pathogenic avian influenza virus that can be transmitted to humans through poultry, has continued to spread in recent years. FAO Chief Veterinary Officer Lubrov pointed out that the H5N1 avian influenza virus has spread in recent years, and H5N1 variant viruses have also appeared in China and Vietnam, which can make existing vaccines ineffective. He called on all countries to be prepared to closely monitor the virus to prevent the spread of the epidemic.

Lubrov pointed out that bird migration is the main culprit in the spread of the H5N1 avian influenza virus, and the production and marketing of poultry has also contributed to the spread of H5N1. He also noted that in the past two years, the virus has been transmitted through bird migration to countries that have eradicated the virus.

Lubrov also expressed concern about the emergence of the H5N1 variant virus in China and Vietnam. He pointed out that this variant virus can defend against the effects of existing vaccines, and urged relevant countries not to be taken lightly and should be fully prepared to monitor the virus.

Virologists warned on Tuesday that no vaccine is available to prevent H5N1 avian influenza variants spread in China and Vietnam, calling on all sectors to step up surveillance of the virus to prevent transmission to humans.

Vietnam's veterinary department is highly vigilant and is said to be considering a new and targeted vaccination campaign in the fall. The spread of the virus in Vietnam directly threatens Cambodia, Thailand and Malaysia, as well as the Korean peninsula and Japan further afield. The migration of wild birds can also spread the virus to other continents.

The United Nations Food and Agriculture Organization (FAO) warned on Monday that bird flu could be swept up again, and said that H5N1 variant strains of bird flu were spreading in Asia and elsewhere.

Scientists are not sure whether the new disease strain H5N1-2.3.2.1 is more lethal to humans, but they point out that the disease strain is significantly different from the original virus, and human vaccines developed against the original virus are not effective against it.

"At present, the World Health Organization (WHO) has recommended an alternative H5N1 vaccine for human use ... but it cannot be completely controlled (new strain)," said Malik Peiris, a virologist at the University of Hong Kong.

"But this is very common. The H5 virus is constantly changing, so we must also develop new vaccines to deal with it." ^[2]

Avian influenza virus prevention and treatment

Avian influenza virus vaccine

Influenza virus vaccination is currently the first choice for humans to prevent influenza. However, due to the large number of influenza virus serotypes, once the antigenicity of influenza virus vaccine strains and epidemic strains do not match, the vaccine will fail and it will not provide corresponding protection; The speed of influenza virus mutation is very fast, and the speed of vaccine development lags behind the speed of virus mutation. After the emergence of new epidemic strains, the corresponding vaccine preparation takes at least 6 months, resulting in the vaccine preparation has been passive. Inactivated vaccines, new vaccines such as genetically engineered vaccines, and nucleic acid vaccines cannot provide cross-protection against all types of influenza viruses.

Avian influenza virus inhibitors

There are two major classes of chemical drugs used to treat influenza: one is ion channel inhibitors, which target the ion channel protein M2 of the influenza virus and block the replication of influenza virus by interfering with the ion channel activity of the influenza virus M2 protein. There are large toxic and side effects, and resistant strains have appeared. The second is a neuraminidase inhibitor, which is an inhibitor targeting the neuraminidase NA of the influenza virus, which effectively inhibits virions by inhibiting the activity of the enzyme

Release on the surface of the host cell membrane, thereby inhibiting the process by which influenza viruses infect new host cells. Resistant strains of the drug have also appeared in patients infected with H5N1 avian influenza virus. In addition, there are some synthetic sialic acid oligosaccharide analogs and single-flavor and compound Chinese medicine preparations against influenza A virus, but they are difficult to promote in a wide range for various reasons. Treatment of poultry and avian flu: Guoco acupuncture 1ml / kg + interferon + cephalosporin, those who are seriously ill can use first aid to interfere with drinking water.

Bird flu virus outbreak in Macau

On March 12, 2014, the Macau Department of Civil Affairs detected H7 avian influenza virus in live poultry samples from the wholesale market. Authorities took immediate action. On the morning of March 13, 2014, more than 7,500 live birds in the wholesale market began to be culled. ^[3]