Etiological Investigation Of M.Gallisepticum In White Meat-type Chickens In Northern Fujian Province And Isolation And Identification Of Epidemic Strains

Mycoplasma gallisepticum(MG)can cause Chronic respiratory disease(CRD)of chicken.Clinical symptoms are mainly coughing,serous rhinorrhea,breathing with difficulty and moist rale.Catarrhal inflammation exudate stuck in nasal meatus and trachea and serious air sacculitis can be seen in the dissection.This disease has a long corse of disease and develop slowly,the death rate is relatively low if there is no other pathogen co-infecting.The cross-infection with Newcastle Disease Virus(NDV)or Infectious Bronchitis Virus(IBV)or Escherichia coli(E.coli)can lead to a higher incidence and death rate,which is a tough problem of large-scale chicken breeding in China.The north of Fujian is the largest breeding district of White Meat-type Chicken in Fujian province.However,there is no relative report of MG infection situation investigation in this area,which makes the effectively prevention of MG infection aimless.Therefore,this research contain the investigation of MG infection situation in the north of Fujian from chicken farming area,at the same time,the isolation and identification of epidemic strains were carried out,the basis of drug sensitivity test of isolated strains and sequence analysis and comparison of pvpA gene sequences,It provides a reference for their prevention and control.Methods:First,Real-time PCR method was used in the investigation of the MG infection situation of White Meat-type Chicken in the north of Fujian province.Secondly,proper Mycoplasma culture medium was chosen from chicken laryngeal tracheal mucus swabs with clinically suspected CDR disease to isolation cultivate and identification for MG,and the clinical isolates were sequenced and compared.At last,choosing 7 clinically-used antibacterials were selected for the Minimal Inhibitory Concentration Test(MIC)to screen sensitive drugs for clinical MG isolates.Result:(1)The positive rate of MG in laryngealtracheal swabs and lung tissue samples was compared by Real-time PCR.The results showed that the positive rates of laryngealtracheal swabs and lung tissue samples were 28.12%and 3.12%,respectively,indicating that laryngealtracheal swabs sampling is more suitable for MG Real-time PCR detection.(2)From March to November 2017,collect 1800 laryngotracheal swab samples from the 90 White Meat-type Chicken farms with different immune backgrounds in north of Fujian Province,The Real-time PCR was used for MG detection,and the results showed that the inoculated with MG vaccine breeder chicken farms were not infected by MG,the MG infection positive rate of commercial broiler farms without MG vaccine immunization is 33.33%,the positive sample rate is 13.17%.The maximum positive sample rate of is 100%,the minimum rate is 5%,and the average rate is 39%.(3)Two strain of Mycoplasma were isolated from laryngotracheal swabs,which were identified as MG,and named as MX isolate and HY isolate.(4)The comparing result of pvpA gene nucleotide sequence showed that the MX isolate and HY isolate are the same.The nucleotide sequence homology with the F strain was 96.7%,there were 10 bases inconsistencies and a loss of 3 bases.The conjectural amino acid sequence homology was 92.2%,and there were 10 differences in which one threonine was deleted.The nucleotide sequence of the R strain was 98.9%,the conjectural amino acid sequence homology was 98%,and the 77 amino acid sequences were missing between DR1 and DR2.The nucleotide sequence of the CG5 strain was 90.9%,the conjectured amino acid sequence homology was 86.3%.Phylogenetic analysis showed that MX isolates and HY isolates were closely related to R strains.(5)The results of animal regression experiments showed that two group of chickens that was inoculated with MX isolate and HY isolate both showed obvious respiratory symptom and the air float both showed pathological changes,like opacity and thickened and foamed,in different level.The chicken in the group that was inoculated with F vaccine strain and the blank control group both were well-developed and no showed obvious clinical symptom.(6)In vitro drug sensitivity test of result showed that the Tiamulin have the best antibacterial effect on MX isolate and HY isolate,followed by Tylosin and Florfenicol.Conclusion:The MG infection situation of commercial broiler of is comparatively severe in the north of Fujian Province.The MX isolate and HY isolate that separated from this district both have pathogenicity.Tiamulin,Tylosin and Florfenicol are the preferred drug to prevention and treatment of CRD.