Chickens Group ? Fowl Adenovirus Pathogenicity Study,Prevention And Control In Jiaodong Area

Adenoviruses are common infectious agents in poultry and wild birds worldwideGroup I fowl adenoviruses(FAdV)are separated into 5 species(A-E),which including 12 serotypes.Among them,FAdV-8b mainly causes inclusion body hepatitis(IBH),while FAdV-4 mainly causes hydropericardium-hepatitis syndrome(HHS).From 2010,IBH caused by Group I fowl adenoviruses has increased in white broiler in China.At the same time,although there were only a few case in 2014,HHS were widely spread all around the country in 2015,and caused significant economic loss.In order to reveal the pathogenic mechanism and pathological characteristics of FAdV,and then formulate effective prevention and control programs and measures for IBH and HHS,and this study needed.By using PCR and gene sequencing and analysis,we tested 455 suspicious samples from 10 different areas(2015?2017),for example,Shandong,Beijing and Henan.Result from PCR showed that there was an increasing from 2015 to 2016,while infection went down in 2017.Shandong,Jiangsu,Henan and Beijing are the most prevalence areas.We also found that commercial layers had a higher infection than yellow birds and white broilers.June to August,and October to November seems to be the most prevalence seasons.Sequencing results showed that FAdV-8b and FAdV-4 are the most dominant serotypes.In order to further study the viral biological characteristics and serological characteristics of epidemic strains in Jiaodong area.By using virus physicochemical characteristic test and AGP test that we isolated one field strain of FAdV-8b(named FXWH-8b)from liver of one suspicious IBH case from broiler farm in 2013,and one field strain of FAdV-4(named FXWH-4)from liver of another suspicious HHS case from broiler breeder farm in Jiaodong in 2015.The virus physicochemical characteristic test showed that the isolated strains were treated with BUDR and sodium hydroxide(pH=10)and 60 degree and lhour respectively.The chicken embryos were inoculated and incubated for 24 hours.The chicken embryos were normal and negative by PCR.However,the strains treated with chloroform and hydrochloric acid(pH=3)did not affect the proliferation of the virus in chicken embryos,and had obvious pathological changes in chicken embryos.The results of PCR were positive.AGP test showed that FXWH-8b strain and the positive sera of FAdV-8b standard strain AV215(FAV-8)reacted positive,while FXWH-4 strain and the positive sera of FAdV-4 standard strain AV211(FAV-4)reacted positive.There's no serologic cross reaction between FXWH-8b and FXWH-4.In order to explore the pathogenicity and it's relative factors of the isolated field strains,we administered the viruses to 15 day old SPF chichens by MI in the leg,and observed the clinical signs.By using PCR,pathological section and immunohistochemical test,results showed that both FXWH-8b and FXWH-4 could make the birds sick,with obvious clinical signs and pathologic changes.Both strains can cause significant pathologic problem in brain,trachea,heart,liver,spleen,lung,kidney,proventriculus,pancreas,duodenum,jejunum,ceca and bursa by HE staining,but we did not find intranuclear inclusion body.Both strains can multiply very fast in various organs after challenge,we found 100%virus recovery from liver,lung,kidney,proventriculus,jejunum and ceca 72 hours post challenge for FXWH-8b,and 48 hours for FXWH-4.Immunohistochemistry showed that FXWH-8b replicated mainly in liver,while FXWH-4 is mainly in liver,kidney,duodenum and jejunum.To solve the problem that there is no commercialized vaccine to prevent FAdV infection in China at present.We prepared vaccines from these two strains,and test the antibody and cross protection of the vaccine.Results showed that both vaccines could have good protection to their own strain challenge,while with no cross protection each other.We also tested the anti-virus protection of the vaccines prepared by three companies by FAdV-4 challenge.Result showed that all the vaccine could protect Group I fowl adenoviruses(FAdV).We further tested four different killed vaccines(prepared by liver of the sick bird of FAdV-8b,infected embryo from FAdV-8b,bivalent vaccine of FAdV-8b and FAdV-4 from infected liver,and bivalent vaccine of FAdV-8b and FAdV-4 from infected cells),with five groups and 32 pen trials.Result showed that killed vaccine prepared from liver of sick bird of FXWH-8b protected FAdV-8b well,but not FAdV-4,while killed vaccine prepared from embryo of FAdV-8b did not protect FAdV-8b and FAdV-4.Bivalent vaccine of FAdV-8b and FAdV-4 from both liver and cell protected well.According to the prevalence and vaccine,we suggest a vaccination program that is:at 6W(s.c),boost at 18W and 22W(i.m),0.5ml per bird each time,and the vaccines are bivalent vaccine of FAdV-8b and FAdV-4 from infected liver,or bivalent vaccine of FAdV-8b and FAdV-4 from infected cells.We also compared the treatment test for astragalus polysaccharides+vitaminC+antibiotic with interferon,results showed that the first one could release the clinical sign of the infection,while interferon could not.A strict biosecurity system and animal welfare program for breeder farm can help to reduce the risk of group I fowl adenoviruses infection.The above results show,this study first investigates the prevalence of group I fowl adenovirus in Jiaodong area,and finds that the group I fowl adenovirus in China has a high incidence trend in recent years.The FAdV strain were isolated from the farm in Jiaodong area,and serum type 8b and type 4 were identified by PCR sequencing and serum test.The pathogenicity study showed that two isolates had strong pathogenicity.This study showed that the therapeutic effect of astragalus polysaccharides combined with vitaminC and florfenicol,developed and screened vaccines with high protection rate.As for the prevention and control of chickens group I fowl adenovirus disease,the author suggested and have proved through practice that the biological safety prevention and control measures can be effectively implemented in the production and management of chickens,and the theory of animal welfare can be properly applied to prevent and control the occurrence of fowl adenovirus disease.