| Avian Escherichia coli(E.coli)is the pathogen of Avian colibacillosis which is one of the most important bacterial diseases in endangering the development of aviculture.The main prevention and control means of Avian colibacillosis are relatively scattered,and there is a lack of precise intervention mechanism in the early stage.For understanding the E.coli epidemic of Chongqing,and establishing a rapid intervention mechanism and efficient prevention and control system for Avian colibacillosis,1866 samples were collected during2016 to 2018 from farms with suspected avian Escherichia coli in 18 areas such as Changshou district,Wanzhou district,Liangping county and Wulong county in Chongqing.The samples included avian epidemic materials,feces,environmental swabs,other animals and flying insects.By means of isolation of bacteria,microscopy and PCR,the samples are analyzed from six dimensions namely source,model,area,month,age and breed;besides,bacterial virulence gene detection and drug resistance analysis are conducted.On the basis of both the characteristics of Chongqing and expert analysis,the avian colibacillosis risk assessment model was established and applied by Delphi method-analytic hierarchy process,Fuzzy synthetic evaluation method and Comprehensive index evaluation method.The study aims to provide basic data and to establish a set of accurate,fast and efficient methods for prevention and control of Avian colibacillosis in Chongqing.1.Isolation,Identification and Phylogenetic analysis of Avian E.coli in Chongqing.By bacterial isolation and identification from 1866 samples,880 strains of E.coil were detected,among which the isolation rate of avian and fly samples were higher than 50%;comparing with other animals in the same spot,the isolation rate of rat was was the highest,up to 59.46%.792 strains of E.coli were confirmed by 16 S r RNA sequencing analysis and weight removal.It showed that there was high homology between avian bar,water sourceand avain E.coil,between pig source and avian E.coil,between fly and avian E.coil.The results indicated that mutual transmission was serious in E.coli among different factors.Phylogenetic molecular clustering results indicated that A(43.18%)and B1(20.55%)group E.coli were dominant groups,followed by B2(23.73%)and D(12.37%)group E.coli which contained strong pathogenicity.2.Analysis of E.coli isolations among different factors.The results are shown as follows: the detection rate of E.coil in rural scattered breeding sites was higher than that of free-range farms and scale farms;the rate of southeast Chongqing was higher than that of northeast and then that of west;the rate in February and August were significantly higher than that of other months,the rank being winter,autumn,summer and spring;the rate of avian's was higher than that of duck and goose;the foreign breeds was higher than that of local breeds;0 ? 5 week-age avian's was higher than that of others,indicating that the younger are more susceptible to infection;the epidemic characteristics of B2 and D group E.coli was similar to the whole groups,indicating that the epidemic characteristics of E.coli have greater correlation to local environment,season and breed.3.Analysis of E.coli virulence genes.The results indicated that the iss?iuc D?irp2 and hly F gene had the highest distribution rate among 286 E.coli isolations in B2 and D groups.There were all-together 72 strains with more than five different virulence genes.Genes like hly F?tsh and aat A were more distributed in western Chongqing,genes like irp2?pap C?cvi/cva gene were more distributed in northeast and southeast Chongqing and iss?iuc D genes presented widespread distribution.In addition,by comparing with the water area map of Chongqing,genes like hly F?tsh?iuc D?iss had high detection rate in areas with plenty of water sources,showing the characteristics of distribution along the Yangtze River.Genes like hly F?irp2?iss?iuc D gene were mostly detected in winter and summer.The pap C gene had the regional and seasonal epidemic characteristics.The iss and iuc D gene were widely distributed in all avian of all day-ages,and there was negative correlation between hly F gene distribution and avian day-ages.Exotic breeds such as hly F?cvi/cva?tsh?ast A genes had higher detection rate,the cvi/cva gene was not detected in local breeds.4.Drug resistance analysis of E.coli.The multiple drug resistance rate in Chongqing was 98.61%.The multiple drug resistance of B2 group E.coli was the most serious.Therewas a significant correlation between drug resistance phenotype and pathogenicity.The multiple drug resistance ratios increased year by year.The avian's was higher than that of human,the exotic breeds were higher than that of local's,the free-range farm's was more serious.Drug resistance of most areas was mainly 12 ? 15 kind of drugs.The western Chongqing was higher than that of southeast and that of northeast.The drug resistance gene of ?-lactam had high detection rate,especially the gene of CTX-M.The detection analysis of drug-resistant genes is similar to the phenotypic analysis of drug resistance.5.Establishment and application of Avian colibacillosis risk assessment model.On the basis of avian E.coli epidemic characteristics in Chongqing,an Avian colibacillosis risk assessment model was established,which contained 5 exponential layers and 38 index layers(the 5 exponential layers being location characteristics,breeding conditions,veterinary foundation,disease situation and medication).At the same time,risk grading was conducted,identifying three risk levels as high,medium and low.For different risk levels,specific prevention and control measures were designed.The risk model was efficiently applied in the case of an infected chicken farm in Wanzhou.After a week of comprehensive prevention and control,the epidemic situation of avian colibacillosis outbreak was relieved,showing the incidence decreased from 9.42% to 4.33%.After another week,no new cases was found.The incidence of avian colibacillosis decreased significantly year-on-year,and remained relatively stable in the whole winter.Therefore,the prevention and control model was proved to be efficient. |
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