Pathogenosis And Genomic Analysis Of Chinese Isolate AH1410 Of Marek's Disease Virus

Marek's disease(MD)is caused by Marek's disease virus(MDV),and primarily occurs in 10 to 12 weeks old hens,cause serious economic losses to poultry industry.Although this disease has been almost well controlled since the wide use of commercial vaccines,MD still occurs even in some flocks which have been vaccinated with MD vaccines.It seems to be very necessary to study the pathogenicity,the characteristics of virus replication in vivo,and the corresponding protective effects of commercial vaccines of the MDV strains in China.The study of the pathogenicity of strains is very feasible for monitoring virus and assessing the effectiveness of current vaccines.The pathogenicity of a strain of Marek's disease virus(MDV)AH 1410 that erupted during the peak of egg production in immunized broiler breeders was investigated.In this resaerch,challenge test,daily observation of clinical symptoms,statistics of body weight changes,pathological necropsy,histological observation of diseased chickens,and fluorescence quantitative PCR detection of viral load in the feathering feathers were carried out to find out whether the virus could really break the immunization protection of the commercial vaccine.It was found that the clinical symptoms such as drooping crown,wingwing,gross disorder,loss of appetite,depression and so on were found in the infected chicken.What's more the results of pathological studies showed that the 7th week after the challenge,the infected group began to die,with a mortality rate of 70%and a tumor incidence of 75%.After 6 weeks of infection,the infected group observed obvious weight loss.It is worth noting that after the course of the disease,the weight ratios of various organs and body weight data were counted,and there were different degrees of difference between each group.What's more,AH1410-infected chickens immunized with the CVI988 vaccine showed a significant reduction in weight gain(p<0.01),resulting in severe immunosuppression,despite of no tumor lesions and death.In order to further understand the genetic characteristics of AH1410 field strain,70 pairs of primers were designed for PCR amplification in this study,and the sequence was made by artificial splicing to obtain the genomic sequences except a-like and VTR section.Phylogenetic analysis of the sequencing results using Dnastar and Mega5.1 software,as well as phylogenetic analysis of important ORFs such as meq and ICP4,demonstrated that the AH1410 strain was more closely related to the Chinese epidemic strains in recent years.In addition,the non synonymous SNP conforms to the specific mutation of the new isolates of China,such as RLORF4 T11M,RLORF7 P176R,UL29 R506L,RSORFI K44 R,and ICP4 K1948M.In a word,our results not only provide a theoretical basis for the better formulation of MD prevention but also provide research directions for the development of more effective MD vaccines.