Isolation And Identification Of Fowl Adenovirus Group Ⅰ From Different Fowl Populations And Its Pathogenicity

Fowl adenovirus serotypes(FAdVs)are present in commercial birds and various wild birds with a worldwide distribution.The epidemiological characteristics of diseases caused by these viruses have been reported in many countries and these diseases have negatively affected the poultry industry.In this study,we collected suspected FAdV infections in some areas of China from 2015 to 2022,and conducted molecular epidemiological investigations and genetic evolutionary analyses of fowl adenovirus group I to provide theoretical references for further related prevention and control efforts.Three hundred and twenty-four suspected infected tissues from six different provinces and regions in China were examined by PCR and sequenced and genetically evolved by amplifying their Hexon genes attached to the pMD19-T vector.In order to better understand the molecular epidemiology of fowl adenovirus group I in Chinese poultry farms.The results of the study showed that the positive detection rate of 324 samples was 23.40%,all from chickens,geese,quails,pigeons and ducks,with a high detection rate of 61.8%for FAdV 2021.Meanwhile,the sequencing results showed that among the 76 sample strains obtained by amplification,6 were fowl adenovirus serotype 1(FAdV-1)6 and 70 were fowl adenovirus serotype 4(FAdV-4).the sample strains of FAdV-1 all belonged to the same genetic evolutionary group.Cloacal swab samples from breeding farms and urinary bladder fluid from breeding eggs were collected for testing,and the study showed that there is a risk of vertical transmission of fowl adenovirus type 4,and clinical chicks with disease at 3-7 days of age may be infected through vertical transmission.In this study,positive samples from three different fowl sources were selected for virus isolation on LMH cells,and FAdV-4 isolates of chicken,pigeon and goose origin were successfully obtained through isolation and purification as well as detection of exogenous viruses.Genetic evolutionary analysis of whole genome sequences showed that the three isolates were located in FAdV-C,with 95.8%～100.0%nucleotide homology with the reference strain of this subline,and each strain The hosts were different,but the genetic evolution was in the same branch,indicating that the fowl adenovirus serotype 4 could infect different avian sources,such as chickens,ducks,geese,pigeons and peacocks,and the virus had some stability,whether it was transmitted across geographical areas or fowl sources,the strains were in the same branch and there was no large variation.In order to study the pathogenicity of different isolates of fowl origin on native animals,we selected isolates for pathogenicity tests on different fowl sources respectively.In the pathogenicity experiments of pigeon origin isolates,20 pigeons were divided into control and attack groups,10 pigeons in each group,and each attack group was inoculated with 2 mL of cell culture solution,and the results showed that the attack group showed different degrees of weight loss or even stopped growing,but did not die until 14 The results showed that the attacking group had different degrees of weight loss and even stopped growing,but did not die until 14 dpi in good mental condition,dissected and killed,dissected and found that a small amount of pericardial fluid could be observed in the pericardium,the liver showed obvious fatty degeneration,turning to earthy yellow,and accompanied by bleeding spots,by making sections to observe the pathological histological changes,the results showed that the hepatocytes of the attacking group had a large number of inclusion bodies and vacuoles,by immune indexes,detoxification detection,tissue loading and cytokine detection and other indicators to The results showed that FAdV-4 of pigeon origin was weakly infectious and pathogenic to pigeons.In the pathogenicity experiment of chickenderived isolates,20 SPF chickens were divided into control group and attack group,10 chickens in each group,and each chick in the attack group was inoculated with 0.2 mL of cell culture solution,and the results showed that the peak of death occurred 2-3 days after the attack,and the mortality rate was 100%.The pathological section showed a large number of inclusion bodies and vacuoles in the liver cells of SPF chickens.In the experiment of pathogenicity of goose origin isolate,20 geese were divided into control group and attack group,10 geese in each group,and each attack group was inoculated with 0.2 mL cell culture solution,the results showed that the attack group showed different degrees of slow weight growth,etc.,and the mortality rate was 30%,and the peak of death was 5～8 dpi until 14 dpi for dissection,and the dissection revealed obvious hepatitis in the liver,which changed to earthy yellow and was accompanied by Hemorrhagic spots,through the production of sections to observe the pathological tissue,the results showed that the attack group hepatocytes appeared a large number of inclusion bodies,through the immune index,detoxification detection,tissue load and the detection of cytokines and other indicators to analyze,goose source FAdV-4 to geese with a certain degree of infectivity and pathogenicity.The test provides reference for the study of the source of infection,transmission route,epidemiological trend and the development of antiviral drugs and vaccines against avian adenovirus in our province.