Diagnosis and control of avian influenza

　　　　Avian influenza (AI) is an acute infectious disease of poultry caused by influenza A virus in orthomyxoviridae. According to the classification of hemagglutinin (HA) and neuraminidase (NA) glycoproteins on the surface of virus particles, it can be divided into many serotypes, and the pathogenicity is different among different serotypes and different strains of the same serotype. At present, the epidemic avian influenza in China is mainly caused by H9 subtype with moderate virulence, which drastically reduces the laying rate of laying hens from 90%-95% to 20%, causing huge economic losses.
　　　　1 Clinical symptoms and pathological changes
　　　　The clinical symptoms caused by the infection of chickens with certain immunity by H9 subtype below moderate virulence or highly virulent strain are generally subacute. Laying hens mainly show different degrees of respiratory symptoms and egg production decline. At autopsy, the larynx and trachea were congested and bleeding, and the blood vessels were blocked by cheese. The fallopian tube is often swollen and filled with albumin-like viscous liquid containing pus. Edema often occurs in the tubal wall and tissues around the fallopian tube.
　　　　2 diagnosis
　　　　The diagnosis of avian influenza is very similar to Newcastle disease (ND), infectious laryngotracheitis (ILT) and bronchitis, mycoplasma gallisepticum (NG), infectious rhinitis, avian cholera, egg drop syndrome and other diseases, so it is difficult to make an accurate diagnosis in clinic, and laboratory tests are needed to confirm the diagnosis.
　　　　2.1 The antibody of blood or eggs was detected by AGID or ELISA.
　　　　2.2 Take cloacal or tracheal smears from sick or dead chickens or take samples from tissues for virus detection at autopsy.
　　　　When chickens are infected with avian influenza virus, antibodies are produced in their blood in about 3-10 days. After about 10–14d days, this antibody can be found in the watery suspension of yolk.
　　　　3 prevention and control
　　　　3.1 According to the actual situation of local and chicken flocks, formulate reasonable immunization procedures and carry out immunization to reduce the occurrence of the disease. At present, the inactivated avian influenza vaccine designated by the Ministry of Agriculture is safe and effective, and is playing an important role.
　　　　3.2 Avian influenza virus is highly variable, and avian influenza immunity presents outstanding blood group-specific protection. Therefore, it is still possible that avian influenza will occur after immunization with avian influenza vaccine. Once avian influenza occurs, intramuscular injection with 3 times the amount of NDI vaccine and anti-stress and antibacterial drugs can effectively control the continued occurrence of avian influenza. This is because in the early stage of avian influenza epidemic, when most chickens were not infected with influenza virus, after NDI vaccine was inoculated, NDI Miao element entered the target cell, on the one hand, the vaccine virus was replicated in the cell (but the vaccine virus had no obvious pathogenic effect on chickens), so that the invaded AIV could not be replicated; On the other hand, the target cell is stimulated by ND vaccine nucleic acid, and interferon is synthesized in the cell, which spreads around through the cell membrane and circulates with the blood flow. After being absorbed by other cells, interferon enters the nucleus, induces mRNA, and produces antiviral protein. This antiviral protein does not damage the cell function, but inhibits the synthesis of RNA (or DNA) polymerase that invades the virus, thus inhibiting the replication of the virus and indirectly playing an antiviral role. It can be seen that early emergency inoculation of DNI vaccine can interfere or inhibit the reproduction of AIV in susceptible cells, and achieve the purpose of controlling avian influenza.
　　　　3.3 If chickens have been infected with AIV, it will be counterproductive to inject with IVD vaccine. At this time, traditional Chinese medicine preparations (such as Folium Isatidis, Radix Isatidis, Rhizoma Coptidis, etc.) can be mixed and fed for 3-5 days, and at the same time, ribavirin or amantadine and antibiotics can be used to drink water, which can relieve symptoms, reduce secondary infection, reduce death and resume laying eggs in advance. Because bird flu has seriously damaged the reproductive system of chickens, it takes a process to restore egg production. With the above drugs, after the diet of chickens returns to normal, the traditional Chinese medicine Zengdan Powder can be fed for 5-10 days, and adding electrolytic multivitamins to drinking water can help restore ovarian function and promote the early recovery of egg production rate.
　　　　3.4 Avian influenza and Newcastle disease are particularly similar in clinical symptoms and pathological changes, which can easily lead to misdiagnosis. However, whether it is avian influenza or Newcastle disease, early emergency vaccination with NDI vaccine can achieve the goal of controlling disease development. If the reason is avian influenza, after inoculation with NDI vaccine, interferon can be produced to interfere with the reproduction of AIV, thus achieving the purpose of controlling avian influenza; If it is Newcastle disease, the injection of NDI vaccine will produce interferon on the one hand, interfere with the replication of Newcastle disease virulent virus, and stimulate the body to produce ND antibody on the other hand, thus achieving the purpose of controlling Newcastle disease.
　　　　3.5 Regular disinfection of the surrounding environment is also a link that cannot be ignored in controlling the disease. AIV is sensitive to water alkali, chlorine preparation, iodine preparation and phenol preparation. (Taiyuan College of Animal Husbandry and Veterinary Medicine, Shanxi Agricultural University, Taiyuan, Shanxi 030024)
　　　　Excerpt from: Livestock and Poultry Industry, No.12, 2002