Artificial Model Of Avian Infectious Bronchitis Disease And Disease Observation

Avian infectious bronchitis disease(IB)is an acute,highly contagious viral disease caused by Avian infectious bronchitis virus(IBV).The disease is generally characterized by respiratory symptoms,which also leads to a drop in egg production.In addition,some strains can cause damage to tissues such as the kidneys and intestines.At present,IBV is prevalent in many countries and regions of the world.In China,the main epidemic strains of this virus were kidney type,and M41 serotype strain was one of them.While the homology of SI gene was 92.1%between the M41 strain and the IBV JS strain,suggesting they may have a closely kinship each other.Therefore,IBV JS strain was used to establish an experimental infection model of avian infectious bronchitis disease in this study,which would provide a powerful theoretical basis for the study of the pathogenic mechanism of domestic infectious bronchitis.1.Invasive approach and dose screening of artificially induced Avian infectious bronchitis disease:The IBV JS strain was selected as the challenge strain in the preliminary experiment.Seventy 10-day-old SPF chicks were randomly divided into 7 groups respectively,named as Tracheal high dose group,Tracheal medium dose group,Tracheal low dose group,Pectoral muscle high dose group,Pectoral muscle medium dose group,Pectoral muscle low dose group.Using the tracheal inoculation and pectoral injection,two ways of attack,manually modeled at the concentration of 106EID50/mL,with 0.2 mL each,0.1 mL each,0.05 mL each three attack doses.Within 144 hours after the challenge,the clinical manifestations of spirit,feeding,drinking,feces and breathing of each group of chickens were observed every 12 hours,and the mortality was recorded.The dead chickens were examined for necropsy and lesions.The results showed that chickens in blank control group were normal in terms of spirit,feeding,drinking,exercise,breathing and excretion.After 24 h,the chickens in the challenge group had fever;until 72 h after challenge,the typical clinical symptoms,such as successive depressions,loss of appetite to abolishment,loose feathers,breathe with a rale through stretching the neck and opening the mouth,mucus in the throat,white or watery diarrhea,caused by IBV were observed.The necropsy of the infected chickens showed bleeding in tracheal ring,yellow or yellow-brown embolism in the lumen,and some chickens showed typical lesions such as kidney swelling.When 0.2 mL/tracheal inoculation,the incidence rate was 100%,the mortality rate was 20%,and the positive rate of IBV detected by PCR was the highest.2.Observation of artificial model of Avian infectious bronchitis disease:70 SPF chickens aged 15 days were randomly divided into the challenge group and the blank control group in the experiment.Based on the results above,the infection group was inoculated with 0.2 mL each at the concentration of 106EID50/mL through trachea.From 24 h after the challenge,on the basis of comprehensive observation of clinical symptoms,each group culled 7 chicks every 48 h for pathology,organ histopathology,immunohistochemical virus detection,serum biochemical and inflammatory factors by Real-time PCR.The chicks in the challenge group had elevated body temperature from 24 h to 264 h after challenge,typical clinical symptoms and typical lesions such as the tracheal mucosa of the larynx begin to appear gradually after 72 h of challenge.The tracheal hemorrhage occurred firstly after 72 h of challenge,while the tracheal mucus embolism was most obvious after 120 h of challenge.Progressive lesions of congestion,hemorrhage,cell degeneration and necrosis in other organs such as liver,kidney,lung,spleen and duodenum were appeared at 72 h and have a certain correlation with the expression levels of IBV,IL-1,IL-6,iNOS,IFN-a and IFN-? in various tissuesThis study established an artificial infection model of infectious bronchitis in chickens,and conducted a more in-depth study of the model from the perspective of pathology,providing scientific and effective data for the dialectical classification of veterinary infectious bronchitis,also lays the foundation for the development of Chinese veterinary medicine with good curative effect,low toxic and side effects.