| Porcine reproductive and respiratory syndrome virus(PPRSV) is the causativeagent of porcine reproductive and respiratory syndrome(PRRS).This disease hasalready been spread to the major swine-raising countries worldwide rapidly since itwas first outbreak in the United States, and has become one of the mosteconomically devastating disease for the global pig industry. PRRSV infection cancause severve reproductive failure,such as premature, abortion, stillbirth, andmummy tire. Furthermore, it can lead to respiratory distress in each age of pigespecially in piglet and high mortality before weaning. PRRSV is a an envelopedvirus containg a single positive-stranded RNA genome. Based on the geneticsequence, it can be divided into two genes types, namely to VR2332strain as arepresentative of the American prototype and LV strain as a representative of theEuropean prototype. PRRSV has highly variation rate, exsting multilevel differenceof gene between strain, especially between the type of European strain andAmerican strain. It indicates that there have many disparities the virulence, genesequence and antigenicity between isolated strains by analyzing.There was an outbreak of PRRS in a pig farm of Myanmar Buddhist state bythe end of2010. We islolated a PRRSV strain successfully from the lung of ill pig.The PAM and Marc-145cells were inoculated with the virus and after48h the cellsappeared charactetistic CPE. Furthermore, we identified by RT-PCR method andimmunofluorescence and designated as Myanmar strain for short. Biologicalcharacteristics of the Myanmar strain showed that pH and temperature environmenthad the greater impact on Myanmar strains；The virus titers began to increase after9h infection in Marc-145cells and to reach the peak of virus multiplication after72h.When infected96h in Marc-145cells, it can be formed medium plaques.Genefragments of Myanmar strain were amplified by RT-PCR and then cloned into thepEASY-T3vector for sequencing. Complete nucleotide sequence of Myanmar strainof PRRSV was obtained by spicing sequence of each fragment in order. The result showed that the genome of Myanmar strain was15411nt in length(excluding PloyAtail), containing10open reading frames(ORFs)with189nt in the5’UTR and151ntin the3’UTR. Compared with American prototype (VR2332) and highlypathogenicity RRRSVprototype (NVDC-JXA1), the genome of Myanmar strainshowed that99.3%and89.5%of nucleotide homology respectively, and no aminoacids deletion was exhibited in nonstructural protein2region. Compared withEuropean prototype(LV), it showed that54.6%nucleotide homology, it indicatedthat the Myanmar strain belongs to the American prototype in genetic diversity. Atthe same time, the phylogenetic tree showed that the Myanmar strain has closerrelationship with PRRSV01NP1.2strain, RespMLV strain, BJ-4strain and PL97-1strain, which infer that the Myanmar strain maybe gradually evolved from abovethese PRRSV strains in Myanmar Buddhist State. The study of biologicalcharacteristics of Myanmar strain lay the theoretical basis for the separation of thevirus, cultivation, preservation conditions and obtainion of high titer virus; Myanmarstrain genome sequence can provide the basic data for PRRSV genetic sequencedatabase, epidemiological investigations, pathogenesis study and research ofgenome structure and function. |
