Avian influenza is a severe infectious disease caused by avian influenza virus, which is mainly prevalent in poultry and wild birds. In particular, highly pathogenic avian influenza has the characteristics of rapid spread, high morbidity and mortality, and great economic losses. The virus not only has many serotypes, but also has the characteristics of many animals and easy variation of strains, which makes it more difficult to prevent and treat avian influenza. In recent ten years, the incidence of avian influenza is faster and the spread is wider, which poses a great threat to the poultry industry. Some virulent strains also cause human influenza. At present, this disease has attracted great attention at home and abroad.

(1) pathogen and its characteristics

Avian influenza virus is a member of influenza virus genus of Orthomyxoviridae, which is divided into three types: A, B and C. Type A mainly infects birds, but people and many terrestrial and aquatic mammals and birds can carry viruses, while types B and C mainly infect people. According to the difference of hemagglutinin and neuraminidase on the surface of virus particles, avian influenza virus can produce more than 100 serotypes, and there is no cross-immune reaction among serotypes, and the pathogenicity and pathological changes among strains are also different. Viruses with high pathogenicity are mainly concentrated in H5 and H7 subtypes, and H9 subtype has strong pathogenicity and virulence, but it is lower than the first two subtypes. According to the epidemic situation of highly pathogenic avian influenza since 2 1 century, the main pathogenic strains are H5N 1, H7N3, H5N9, H5N8, H5N2, H7N7, H7N4, h7n01. The epidemic situation of avian influenza in China is mainly caused by H5 and H9 subtype avian influenza viruses, which provides a basis for vaccine production and immunization of avian influenza.

Avian influenza virus is sensitive to the external environment and its resistance is weak. Sunlight, drying, heating and various disinfectants can kill it. Such as heating at 60℃ 10 minute and heating at 70℃ for 2 minutes, it can be inactivated. The virus can be inactivated in direct sunlight for 40 ~ 48 hours. Many disinfectants, such as sodium hydroxide, disinfectant, chlorpyrifos, bleaching powder, formalin and peracetic acid, can effectively kill viruses at common concentrations. Accumulation of fermented poultry manure,10 ~ 20 days can completely kill the virus. Avian influenza virus has strong resistance to low temperature and humidity and has a long survival time.

(2) Prevalence and its symptoms

Avian influenza mostly occurs in the alternating seasons of winter and spring, autumn and winter, mainly in horizontal transmission, and can also spread vertically through eggs. The source of infection can come from infected and diseased poultry, wild birds and migratory waterfowl. Pathogens pollute the environment, feed and drinking water through secretions, excreta and corpses, and become infected through direct or indirect contact. Respiratory tract and digestive tract are the main routes of infection.

After poultry is infected with avian influenza, the incubation period varies from several hours to several days, and the symptoms vary according to poultry breed, age, virulence of virus strain and secondary infection or not. The main manifestations are increased body temperature, depressed spirit, decreased or stopped feeding, loose feathers and decreased egg production15% ~ 70%. There are respiratory symptoms, such as cough, sneezing, dyspnea and purple comb. The sick chicken shed tears, and the head and face became edema. Some of them have neurological symptoms, head and neck torsion and * * * ataxia. Those with a longer course of disease are often accompanied by secondary infection. In the acute outbreak caused by virulent strains, chickens died in large numbers without obvious symptoms, and the mortality rate could reach 80% ~100%. The mortality rate of non-acute outbreaks varies from10% to 50%.

In recent years, avian influenza in poultry has the following characteristics: first, avian influenza occurs in a certain area, and the virus strains are relatively single, and it is rare that two or more strains act together. Second, the loss degree of the disease is related to the poultry species besides the virus virulence. What is sensitive to chickens is not necessarily sensitive to ducks and geese. Third, the same species of poultry, high-yield and fast-growing improved varieties of poultry are more sensitive than local varieties of poultry. The fourth is the age difference. The resistance of old chickens is stronger than that of young high-yield laying hens. The fifth is the health status of poultry. When the poultry population is in good health, the disease loss is small and the symptoms are light. Sixth, it is related to stress. The symptoms of unstressed poultry after onset are lighter than those of stressed poultry. Seventh, secondary infection or not. Poultry only suffers from avian influenza without secondary infection, and its loss is less than that of poultry with secondary infection. Once avian influenza occurs, early detection and early control of secondary infection with antibiotics can effectively reduce the incidence loss. Eighth, the immune effect of fast broilers on H9 subtype vaccine is not ideal, and the reasons need to be further studied. Nine, the chickens with high antibody level of Newcastle disease have less loss when avian influenza occurs than those with low antibody level, which may be due to the effect of interferon produced by Newcastle disease immunization on avian influenza virus.

(3) Prevention and control measures

1) Do a good job in immunization.

Immunization is the most important measure to control the epidemic of avian influenza. At present, there are two kinds of avian influenza vaccines: univalent vaccine and bivalent vaccine. Because there is only one serotype of avian influenza prevalent in a certain area, it is feasible to inoculate univalent vaccine by mastering the epidemic strains of local diseases, which is beneficial to accurately monitor the epidemic situation. When the serotype is unknown in the region, 2 ~ 3 valence vaccine can be used for immunization. The protection period after vaccination can generally reach 6 months. In order to maintain a reliable immune effect, vaccination should be strengthened every 3 months. It is suggested that 0.3 ml per chicken should be injected subcutaneously or intramuscularly at the age of 5 ~15 days. 50 ~ 60 days old, 0.5 ml for each chicken. Three exemptions were given before opening, with 0.5 ml for each chicken. Commercial laying hens and breeders can be exempted for four times at the age of 40 weeks in the middle of laying.

2) treatment

Highly pathogenic avian influenza in poultry should be resolutely culled and eliminated, and mild avian influenza can be treated with drugs.

(1) Antivirus: Chinese herbs such as Folium Isatidis, Radix Isatidis, Rhizoma Coptidis and Radix Astragali can be decocted in water to make poultry drink.

② Control of secondary infection: When avian influenza is found, antibiotics should be used to control secondary infection as soon as possible. For example, add 50 ~100 mg of enrofloxacin to every liter of water for 4 ~ 5 days; Add 5 grams of oxytetracycline to the feed per 100 kg. In order to improve the constitution and disease resistance of poultry, multi-dimensional electrolytes can be added to drinking water at the same time.

3) Strengthen the comprehensive control measures for the epidemic of avian influenza.

① Do not introduce from epidemic areas or areas with unknown epidemic situation. Do not bring fresh livestock and poultry products from outside into poultry farms.

② The varieties of poultry raised in poultry farms should be consistent, and different varieties of poultry or livestock and poultry should not be mixed, and the feeding system of "all in and all out" should be implemented;

(3) it is strictly forbidden for outsiders and vehicles to enter the poultry farm, and they must be disinfected if they really need to enter. Poultry workers should wear work clothes, work boots and masks when going to work, and they must change clothes when entering and leaving the poultry farm. Vehicles for transporting feed and poultry products in production should be used separately.

④ Control other animals to carry poison. Poultry farms do not plant tall trees, and try to use grass floors to green the environment to prevent wild birds from gathering; Rodent control activities are often carried out, and there are no pigs, dogs, cats and other animals in the production area. Although these animals do not have bird flu at present, they often carry poison.

⑤ Self-provided drinking water system adopts deep well water or tap water instead of river, lake and pond water.

⑥ Poultry manure and padding are piled up for fermentation or incineration for not less than 20 days.

⑦ Strengthen feeding management. In the high-incidence area, peracetic acid and sodium hypochlorite can be used for1~ 2 times a day to disinfect the poultry and the environment, and the poultry can be disinfected every 2 ~ 3 days at ordinary times. Try to avoid all kinds of stress reactions, and if necessary, add 0.0 1% vitamin C and 0. 1% vitamin E in feed or drinking water to improve the stress resistance of poultry. Provide feed necessary for production, growth and development, and keep the feed fresh and complete. Improve the feeding environment and provide suitable temperature, humidity, density and illumination; Strengthen the ventilation of poultry houses to keep the air fresh; Regularly clean feces and poultry houses and the environment to keep the production environment clean and hygienic.

⑧ After each batch of poultry comes out of the cage, the empty period is not less than 3 weeks, and the poultry house shall be treated according to the cleaning and disinfection procedures of cleaning → cleaning → drying → disinfection → cleaning → finally closed fumigation. Use more than two disinfectants to remove pathogen residues in poultry houses and prevent pathogens from infecting the next batch of poultry.