Epidemiology of Avian Leukosis Viruses in Wild Birds and Pheasants
|Shandong Agricultural University
|Basic Veterinary Science
|Wild bird Pheasants Avian leukosis virus Epidemiology
Avian Leukosis is caused by avian leukosis viruses (ALVs), which belong to the genusAlpharetrovirus of the Retroviridae family, cause neoplastic diseases and other reproductionproblems. The ALVs can be classified as endogenous (ALV-E) or exogenous virusesaccording to their mode of transmission. Exogenous ALVs from chickens have been furtherdivided into different subgroups (A, B, C, D, and J) on the basis of their host range, viralenvelope interference, and cross-neutralization patterns. The ALV-A infection is commonclinically, but ALV-B is rare. People did not take enough consideration in ALV due to thelittle loss in pouLtry industry until late20th century, ALV-J broke out worldwide. The pastmolecuLar epidemiology studies were mainly focused on pouLtry and waterfowl, and reportsof infection in wild birds and pheasants were rare. To analyze the status of wild birds andpheasants infected with avian leukosis virus (ALV) in China, in our study, the epidemiologyof ALV-A, B, J in the wild birds of northeast China in2010-2011was studied, importantgenes were sequenced and analyzed;152blood samples were collected from8farms inPingyuan County, Dezhou, Shandong Province, in order to detect the antibody level byELISA. The results were as followed:2ALV-A,4ALV-B and7ALV-J positive sampleswere detected by PCR using specific primers from the300samples of wild birds; according tothe sequence of the ALV-J strain, HPRS-103(GenBank accession number Z46390),4specific primer pairs were designed and the whole genome of one ALV-J strain (WB11098(J))was successfully amplified.Env genes of13positive samples were amplified and the sequences were analyzed andcompared with the representative strains of ALV-A,B,J, respectively. The results were asfollowed:(1) The phylogenetic analysis indicated that the gp85genes of2ALV-A strainswere97.6%identical to American strains MQNCSU, indicating that ALV-A found in wildbirds most likely came from American chickens;(2) The phylogenetic analysis indicated thatthe env genes of4ALV-B strains showed highest homology to prototype strain RAV-2andAmerican strains Schmidt-Ruppin B, indicating that ALV-B found in wild birds most likelycame from American chickens;(3) The phylogenetic analysis indicated that the env genes of7ALV-J strains showed highest homology to Chinese strains JL08CH3-1, which is differentfrom ALV-A and ALV-B.The whole genome of WB11098（J）was sequenced and analyzed, the results showed that the length is7869bp. Compared with the representative strains, WB11098(J) has thefollowing features:(1)in the5′LTR,5nucleotides(TGTTAT) insert before the site one.9nucleotides (ACTCTTGTA) insert between site11and site12, resulting in the loss of C/EBPelement. One nucleotide changes(“A” to “G”) in site107in AIB REP1element, otherelements are relatively conservative;(2)in the5′UTR, the length is398bp,19nucleotidesinsert between site362and site363, besides,29nucleotides varied;（3）gag and pol genes ofWB11098(J) were highly conserved, but env genes were highly varied and many amino acidsmutate. The mutations mainly occur in the gp85genes, and the changing of nucleotides willlead to the changing of chemical property of amino acids.4positive blood samples were detected from152ones:3ALV-A, B and1ALV-J.Special poultry (for example Luhua chicken, hemp chicken) infecting the ALV had beenreported. Though the detecting rate is low, the vertical and horizontal transmition of ALVsand the potential threat must be taken into our considerationIn the study,13positive samples were detected from the300samples of wild birds,which will provide rich materials for the researches on ALV pathogenesis to wild birds. Thepast molecular epidemiology studies were mainly focused on meat-and egg-chickens, andreports of infection in wild birds were rare, besides, the highly mutated genes were cloned inorder to analyze the source of ALV in wild birds. To study the molecular features of ALV inwild birds, one whole genome of WB11098(J) were cloned and analyzed.4positive bloodsamples were detected from152ones by ELISA, which enable us to understand the situationof infection of ALV of domestic chicken.