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| What is the influenza A virus? What are the characteristics, manifestations, complications, and prevention methods of influenza A? |
Influenza A virus is a common influenza virus, and influenza A virus is the most susceptible to mutation. The subtype of influenza A virus is called "bird flu". Bird Flu is a kind of bird flu virus. Acute infectious diseases, virus gene mutations can infect humans, the symptoms after infection are mainly high fever, cough, runny, myalgia, etc., most of them are accompanied by severe pneumonia, severe heart, kidney and other organ failure leading to death The mortality rate is very high. The disease can be transmitted through digestive tract, respiratory tract, skin damage and conjunctiva. People and vehicles are important factors in the spread of this disease.
Influenza A is highly pathogenic to humans and has caused worldwide pandemics. Among the influenza A viruses, the avian influenza virus subtypes that have been found to directly infect humans are: H1N1, H5N1, H7N1, H7N2, H7N3, H7N7, H7N9, H9N2 and H10N8. Among them, H1, H5 and H7 subtypes are highly pathogenic, and H1N1, H5N1 and H7N9 are particularly worthy of attention.
Virus profile
Influenza A virus is a common influenza virus. It is mainly susceptible to mutating while the main subtype is called some bird flu, so it is also an acute infectious disease in daily life, and after infection. The main symptoms are some high fever, some cough, some pneumonia and some small dysfunction, so it is necessary to treat and prevent it in time.
Principle of action
Influenza viruses are classified into three types: A, B, and C. Influenza A is the most susceptible to variability. The influenza pandemic is caused by the emergence of new subtypes or old subtypes of influenza A virus. The surface antigen of influenza A virus often undergoes small mutations. This mutation is called "drift". In the image, "floating" means that the virus disguise itself through small changes, thus avoiding the immune system. The purpose of identification. The result of the "floating" of the A virus is that the strains that cause the flu every year are likely to be different, and people need to re-vaccinate the flu vaccine every year for prevention. "Shift" refers to a mutation in the influenza A virus that causes a new viral "subtype" to appear. Because there are few antibodies against this new virus in the human body, the result of "shifting" often leads to a global outbreak of influenza. Influenza viruses usually rely on the combination of a certain part of the viral protein with a specific protein in the human body to invade the human body. Because of this combination, the influenza virus can inhibit the body's own natural defense system against viral infection, paving the way for the virus to effectively replicate in the human body. .
Influenza viruses are classified into three types: A, B, and C. Influenza A virus is divided into many subtypes according to H and N antigens. H can be divided into 17 subtypes (H1 to H17), and N has 10 subtypes (N1 to N10). Among them, only H1N1, H2N2, and H3N2 mainly infect humans, and many other subtypes of natural hosts are a variety of birds and animals. Among them, H5, H7 and H9 subtype strains are the most harmful to birds. Under normal circumstances, the avian flu virus does not infect animals other than birds and pigs. However, in 1997, Hong Kong reported for the first time 18 cases of H5N1 human avian influenza infection, of which 6 died, causing widespread concern worldwide. After 1997, there have been several incidents of avian influenza virus infection in the world. The highly pathogenic avian influenza viruses such as H5N1, H7N7, H7N9, and H9N2, once mutated and have human-to-human transmission ability, will lead to the epidemic of human avian influenza, indicating that the avian influenza virus has great potential for humans. Threat.
Antigenic variation
The variation of influenza virus is most important in type A and is often closely related to the worldwide pandemic. In general, the antigenic variation of influenza viruses refers to changes in the structure of H and N antigens, and small variations (quantity changes) often occur within subtypes, called antigenic drift. Although it is only a minor variation, it allows the virus to easily escape the host's immune system. If a mutation occurs on a hemagglutinin molecule-specific antigenic determinant (epitope) compared to the previously discovered strain, the new strain is considered to be a heterogeneous variant of the previous strain, with epidemiology The meaning can cause the flu epidemic.
Antigen variation occurs only in the alphavirus. It may be due to the fact that the same cell is infected with two viruses of humans and animals, and genetic recombination occurs between the viruses. The resulting viral hemagglutinin and neuraminidase are completely combined, making the population immune. Antigen transformation is the cause of the global pandemic of influenza. Influenza A virus has undergone a major mutation every ten years or so. Since 1933, the A virus has undergone four antigenic transformations: from 1933 to 1946, it was H0N1 (formerly A, A0), and from 1946 to 1957. H1N1 (Asian type, A1), H2N2 (Asian type A, A2) from 1957 to 1968, H3N2 (Hong Kong type, A3) after 1968. There is a clear alternation between the old and new subtypes. After the new subtypes appear and become popular in one area, the old subtypes can no longer be separated. There is also a large variation and a small variation in the type B infection, but it is not divided into subtypes. No antigenic variation has been found in influenza C virus.
Epidemic hazard
Source of infection
The source of the flu infection is mainly the patient, followed by the latent infection. Animals may also be important storage hosts and intermediate hosts. The patient can discharge the virus from the secretions such as nasal discharge, mouth sputum and sputum within 5 days after the onset of the disease. The infection period is about 1 week, and the infection is the strongest at 2 to 3 days.
way for spreading
Airborne droplets are the main source of transmission, followed by indirect transmission of virus-contaminated tea sets, utensils, towels, etc. Close contact is also one of the ways to spread the flu. The speed and breadth of transmission are related to population density.
Virus characteristics
Susceptibility
For influenza virus, the population is generally susceptible. The antibody appears 1 week after infection or vaccination, peaks in 2 to 3 weeks, begins to decline after 1 to 2 months, and falls to a lower level in 1 year or so. Influenza virus 3 types There is no cross immunization between.
Seasonal
Similar to many other respiratory viral diseases, influenza is also a seasonal disease. It has a low incidence in summer and a high incidence in winter, but in some places the virus is prevalent throughout the year. The onset time of the flu is related to the geographical location. In the temperate zone, the flu is prevalent throughout the winter, the northern hemisphere usually peaks in January and February, and the southern hemisphere is late. Usually in May to September. In the tropics, influenza viruses are present throughout the year and tend to be popular during the rainy season.
Historical case
The flu is characterized by recurrent, unpredictable local epidemics and rare global pandemics. In some years, the local epidemics of influenza are caused by the emergence of new influenza strains due to antigenic drift, and some people lack or no protective measures. There have been several worldwide pandemics caused by mutations in the influenza A virus antigen since 1889.
The pandemic from
1.1889 to 1891 was discovered in Russia in May 1889. It was transmitted to Western Europe in October of that year and swept the world within one year. In some cities, the incidence rate was 40% to 50%. In most areas, there are three waves, the first wave has the lowest mortality rate, the third wave has the highest mortality rate, and the majority of the deaths are elderly. According to serological traceability, type A is the most likely pathogen of the pandemic.
2.1918 to 1920 The popular launch was first held in the eastern United States in January 1918. It was popular among French troops in April 1918 and spread rapidly around the world. The pandemic is known as the largest plague in human history, and the total number of deaths is estimated at about 20 million. The pathogen of this pandemic, according to serological traceability, is thought to be caused by the swine Hsw1N1 (H1N1) influenza virus.
3.The pandemic from March 1957 to 1958 was first launched in western China in February 1957. In mid-February, the virus was isolated from Guiyang as H2N2 (called A2). It spread to the whole country in March, and was popular in Hong Kong in April. Japan spreads to the whole world. After the emergence of the H2N2 virus, the H1N1 virus disappeared in the human population.
4. Pandemic from 1968 to 1969 In July 1968, new subtype influenza was prevalent in Guangdong and Hong Kong, and the newly isolated viral antigen was H3N2 (called A3). The transmission route is similar to the H2N2 type. It spread globally from 1969 to 1970 and was lower than H2N2. After the emergence of the H3N2 virus, the H2N2 virus disappeared in the human population.
5. In 1976, a small outbreak of swine influenza occurred in the United States. In January 1976, there was an outbreak of influenza in a US barracks. Of the isolates, 6 belonged to type A3, but 5 strains were very similar to the swine type virus Hsw1N1 (H1N1). A mixed epidemic of type A and pig type occurred in the barracks. The cases of swine influenza were lighter than those of the type A.
6. The emergence and prevalence of new type 1 (H1N1) in 1977 In May 1975, in the influenza epidemic in Dandong, Anshan and Tianjin, the new type A was isolated. After July 1977, it spread from north to south, and then spread throughout the country. But did not cause a worldwide pandemic. The prevalence mainly occurs in adolescents aged 8 to 20 years, with more recessive and light infections. After the emergence of the new type A, the type A 3 did not disappear, and there was a situation in which the 1st and the 3rd were coexisting in the crowd.
Causing losses
The flu epidemic is accompanied by an increase in mortality. The increased mortality rate is not only caused by influenza and pneumonia, but also by the spread of cardiopulmonary diseases and other chronic diseases caused by influenza. In the US 1972-1995 influenza epidemiological study, influenza epidemics occurred 19 years in 23 years and caused excessive deaths. In 11 different influenza epidemics, it is estimated that there are 20,000 flu-related deaths each time, of which more than 40,000 are in six. Of the 11 epidemics, more than 90% of deaths occur in older people over the age of 65. Older people, children, and people of any age who are over 65 years of age are at higher risk of complications, hospitalization, and death from flu due to flu. For example, the hospitalization rate in the 0-4 age group is 100/100,000 for healthy children and 500/100,000 for children with underlying diseases.
According to some survey results, France’s health service fees for flu in 1989 were about 1.9 billion francs, and the potential economic losses were as high as 14.3 billion francs. The direct economic loss caused by the flu in the United States is between $1 and $3 billion per year. The potential economic losses are as high as $10-15 billion. The recent outbreak of bird flu in Hong Kong, China, is estimated to have lost as much as 80 million Hong Kong dollars. China is a high-incidence area of influenza. Three of the four world influenza pandemics that occurred in the 20th century originated in China. In recent years, most of the newly discovered influenza strains have originated in China. From 1953 to 1976, there have been 12 epidemics of moderate or moderate influenza in China. Although detailed epidemiological data are still lacking, it is certain that the annual economic loss caused by influenza in China is also very alarming.
Japan has adopted a method of immunizing school-age children in the control of influenza. From 1962 to 1987, Japan vaccinated most school-age children with influenza, reducing the original high mortality rate from three to four times that of the United States to the same level as the United States. The immunization measures save 37,000 to 49,000 people in Japan every year, that is, one 420 children can save one elderly from death. In the United States, the use of influenza vaccines has steadily increased throughout the 1990s, reaching 281 vaccines per 1,000 people in 1997. In the same year, 29 countries in Western Europe have made age-based recommendations for influenza vaccination. Vaccination rate for the elderly: 70% in France, 45% to 50% in Belgium, 36% in Italy, and 65.5% in the United States. Many of these countries provide the cost of influenza vaccination through national financial or social health insurance, and provide free vaccination for some people who recommend vaccines. Of course, in most countries, most people still pay for the flu vaccine at their own expense. Vaccine use levels in different countries have nothing to do with per capita health costs. The level of vaccine use reflects the importance of flu and the effectiveness of vaccination. Moreover, vaccination is the best preventive measure of cost-benefit ratio. According to the survey, the annual direct medical expenses for influenza in the United States is 4.6 billion US dollars, and the average annual savings of 117 US dollars per vaccination per person; for the company, the investment of 1 US dollar can save the company 2.58 US dollars. In Argentina, due to the implementation of the vaccination program, each vaccinated child saved $10.04.
Infection performance
The severity of influenza is related to the individual's immune status. In general, only about 50% of infected patients develop clinical symptoms of typical influenza. Typical symptoms of flu are sudden fever, dizziness, headache, myalgia, mild systemic symptoms, and may be accompanied by sore throat and cough, stuffy nose, runny nose, chest pain, eye pain, photophobia and other symptoms. The body temperature of the fever can reach 102 to 104 °F, and it usually retreats after 2 to 3 days. Generally, the systemic symptoms are heavier and the respiratory symptoms are not serious.
Complication
The most common complication is pneumonia. Generally, secondary bacterial pneumonia is more common, and Staphylococcus aureus, pneumococcus and Haemophilus are more common. The primary influenza virus pneumonia is rare, more common in patients with heart, lung disease (especially rheumatic heart disease, mitral stenosis) or pregnant women, the mortality rate is higher.
Other complications include Reye's syndrome, toxic shock syndrome. Reye's syndrome is limited to children between the ages of 2 and 16 and is mainly associated with influenza B (or chickenpox, herpes zoster). Clinically, after several days of acute respiratory infection, neurological symptoms such as nausea, vomiting, and then lethargy, coma, and convulsions are further developed into coma. In recent years, it has been considered to be related to taking aspirin. Toxic shock syndrome often occurs after the flu, accompanied by respiratory failure, chest radiograph can show adult respiratory distress syndrome, but the pneumonia lesions are not obvious. There may be an increase in influenza antibodies in the blood, and pathogenic bacteria can be found in tracheal secretions, and Staphylococcus aureus is more common.
Solution
Vaccination against influenza is the most effective way to avoid getting the flu. Since the influenza virus often mutates, the main problem in the use of the vaccine is the selection of the virus species, and the strain producing the vaccine seeks to approach the epidemic strain. In September and February each year, the WHO Global Influenza Planning Group recommends that the southern hemisphere usually use the ingredients of the flu vaccine in the next flu season starting in May-June and starting in the northern hemisphere from November to December. The composition is based on monitoring data from the global network of the National Influenza Centre and the WHO Collaborating Centre. The current influenza vaccine contains two subtypes of influenza A virus antigens (H3N2 and H1N1) and one influenza B virus antigen. There are 3 types of these vaccines.
- The whole virus vaccine consists of the entire inactivated virus, so the side effects are relatively large. The method of inoculation of whole virion vaccines has been largely replaced by other methods.
- The split virus vaccine consists of virus particles lysed by detergent treatment, and the split influenza vaccine includes components such as surface antigen, hemagglutinin, neuraminidase, nuclear protein and matrix protein. This vaccine is suitable for adults and children.
- Subunit vaccines are mainly composed of HA and NA which have been removed from other viral components and which only produce an antibody protection reaction. Due to its high purity, safety and tolerability, it is especially suitable for children.
Influenza vaccines usually do not have adjuvants. However, the European Union has recently approved a subunit vaccine containing a new oil-in-water adjuvant (MF59). This vaccine seems to enhance the antibody response in the elderly, but the clinical significance of this study needs to be further elucidated. Influenza live vaccines have been used in the former Soviet Union and other countries. Nasal application trials of live influenza vaccines are currently being conducted in the United States.
The effectiveness of existing inactivated influenza vaccines for high-risk populations has been confirmed, but their protective period is limited, requiring annual vaccination, possible side effects after injection, and lack of local and cellular immunity, prompting the development of a spray-type reduction Live flu vaccine. In the early days, spray-type attenuated influenza live vaccines were developed in the former Soviet Union and Japan, but the reported validity data is not convincing. Recently, cold-adapted and reassortant strains have undergone more thorough tests and achieved excellent results. Child trials have shown to be highly effective, and adult trials have shown that live vaccines have a synergistic effect on the immunogenicity of inactivated viruses.
Influenza vaccination can prevent influenza virus infection and prevent avian influenza virus. However, according to the WHO “Guidelines on the application of influenza vaccine in high-risk populations of H5N1 virus infection”, although the influenza vaccine cannot protect the vaccinators from the infection of H5N1 highly pathogenic avian influenza virus, it can reduce the vaccination of both vaccinated persons and avian flu. The chance of a viral virus, thereby reducing the chance of viral genetic recombination of the influenza virus and reducing the risk of a new influenza pandemic.
Prevention tips
To prevent influenza, in addition to flu vaccine, you should also pay attention to personal hygiene habits:
- Pay attention to personal hygiene, develop good personal hygiene habits, wash hands frequently, take a bath, do not share towels, cups and other daily necessities, so as not to spit, in order to prevent contact with the spread of influenza virus.
- The room and the office, should be frequently ventilated, reduce the number of bacteria and viruses gathered indoors, keep the indoor fresh air.
- The disease epidemic should be avoided as much as possible in public places, such as shopping malls, cinemas and other crowded places. Keep a distance of more than 1 meter from those who sneeze.
- To the hospital to see a doctor, it is best to wear a mask. Most of the respiratory diseases are transmitted by the air, and patients in the hospital are mostly patients with various diseases and are easily infected. Wearing a mask can effectively block bacteria and viruses. At the same time, washing hands frequently has a certain effect on preventing influenza.
- It is necessary to appropriately increase or decrease clothes according to changes in temperature to prevent low immunity caused by colds and colds.
- Daily diet should pay attention to balanced nutrition, regular quantitative, drink plenty of water, no smoking, less alcohol. At the same time, it is necessary to ensure adequate sleep and avoid overwork.
- To strengthen physical exercise, often adhere to outdoor sports to enhance physical resistance. In particular, teachers and students of large, middle and primary schools living in group life should go outdoors to carry out sports activities, work and rest, maintain normal study and life, and minimize indoor activities and gatherings.
Ways to prevent flu: the sheets should be washed frequently, and the quilts should be exposed to the sun often, killing harmful bacteria; in places with dense crowds, it is best to wear a mask; keep the air in the room, often open the window, keep The room is clean and hygienic; the climate changes very quickly, remember to increase or decrease the clothes, be careful of colds; enhance physical fitness, exercise, do some aerobic exercise, enhance the body's immunity; when you come back, remember to wash your hands, try not to touch your eyes with dirty hands. , nose, mouth; diet is light, do not eat too much spicy and cold food. For antiviral treatment, there is now a localized oseltamivir phosphate in China. Compared with imported drugs, its efficacy and safety are equivalent. And Kewei not only has a capsule dosage form, but also innovatively developed a granule type for children to take. When is the flu vaccine? The flu vaccine is best vaccinated in the fall, because the temperature changes greatly in autumn and winter, and it is the high incidence of flu. After the winter, when the spring blooms, the flu will disappear. A shot can generally be used for half a year. After half a month of vaccination, it can produce viral antibodies, enhance human immunity, avoid getting sick at the peak of the flu, and pay attention to the vaccine. At the peak of the flu, remember to pay more attention. Rest, light diet, enhance physical fitness, exercise.
Typical case
Avian influenza is the abbreviation of avian influenza, a contagious disease syndrome caused by a subtype of influenza A virus. It has been designated as a Class A infectious disease by the International Bureau of Animal Diseases, also known as true chicken or European chicken. . Not only chickens, but also some other poultry and wild birds can be infected with bird flu. According to the type of pathogen, avian influenza can be divided into three categories: highly pathogenic, low pathogenic and non-pathogenic. Non-pathogenic avian influenza does not cause obvious symptoms, only virus antibodies are produced in infected birds. Low pathogenic avian influenza can cause mild respiratory symptoms in poultry, reduced food intake, decreased egg production, and sporadic deaths. Highly pathogenic avian influenza is the most serious, with high morbidity and mortality, and infected flocks are often “overwhelmed”.
The earliest avian flu was recorded in 1878, and a large number of chickens died in Italy, which was known as chicken cockroaches. By 1955, scientists confirmed that the pathogenic virus was an influenza A virus. Since then, the disease has been renamed to bird flu. Avian flu has been discovered for more than 100 years. Humans have not mastered effective prevention and treatment methods, and can only prevent it from spreading by disinfecting, isolating, and slaughtering livestock in large quantities. Areas with high pathogenic avian influenza outbreaks often suffer huge economic losses.
In general, avian influenza viruses are not easy to cause human disease. The avian influenza virus is an influenza A virus, and the influenza A virus is classified into 15 subtypes such as H1 to H15 depending on the surface protein. Avian influenza is caused mainly by the highly pathogenic H5 and H7 subtypes, and humans are susceptible to the H1 and H3 subtypes.
The current avian influenza virus circulating in South Korea and Japan is H5N1 type, which is usually transmitted only in poultry and rarely infects humans. Although there have been cases of human infection with avian influenza virus, such as the 1997 Hong Kong avian flu that caused 12 people to suffer from illness, 6 of them died, but this situation is rare. In addition, human infection with avian influenza virus is mainly caused by contact infection, and no cases of infection due to eating chicken and eggs have been found. From a microbiological perspective, there are three reasons for preventing the avian flu virus from invading humans. First, human respiratory epithelial cells do not contain specific receptors for avian influenza virus, ie, avian influenza viruses are not easily recognized and bound by human cells; second, all influenza viruses that can be prevalent in the population must have several human influenza in their genomes. The gene fragment of the virus; third, the highly pathogenic avian influenza virus has a large number of basic amino acids, making it difficult to replicate in the human body.
However, although there is no evidence that the avian flu virus directly causes human influenza outbreaks, from an evolutionary perspective, human influenza is associated with influenza viruses that were previously transmitted in animals. It is likely that in the history of human domestication of pigs, chickens and other animals, due to frequent human and animal exposure, certain strains of swine flu and avian influenza viruses have mutated, obtained pathogenicity to humans and spread among people. Ability to become a human influenza virus. Such incidents are likely to happen again, so the medical research and monitoring department remains vigilant about the possibility of bird flu attacking humans. For individuals, they should pay attention to good health and maintain good immunity; before eating poultry products, they should be cooked at high temperature to kill the virus. As of now, there have been no cases of people infected with the highly pathogenic H5N1 avian influenza virus in mainland China. China has established a technical means to quickly detect avian flu. The Ministry of Health strengthened surveillance of influenza epidemics including avian flu a few years ago. The trends of various influenza viruses are in the field of surveillance.
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