Investigation On Epidemiology Of Porcine Reproductive And Respiratory Syndrome In Shandong Province

Porcine Reproductive and Respiratory Syndrome (PRRS) broke out first in America in1987, and then went through worldwide quickly with clinical signs of abortion, such as death mummy and respiratory diseases in pigs with various age. The pathogen of PRRS was first detected by Wensvoort in 1991 in Hollan. The first PRRSV in China was isolated in swine with suspected PRRS in 1995 by Baoqing Guo, confirming that PRRSV had spread in China, and then followed by other PRRSV found in most of China."Swine High Fever Disease"broke out in Autumn in 2006 nationally, it is confirmed that this epidemic disease is maked by aberrant Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) . For the sake of instance about popularity of PRRS in Shandong, The studies put emphases on clinic, serology, molecule biology and so on. Accordingly to offer the theory basis for the prevention and control this disease .This study included as following:1, In the present study, To assay the infection of Porcine reproductive and respiratory syndrome (PRRS) in Shandong, 601 serum sample vaccinated from sixteen pig farms and 227 ones non-vaccinated from eight farms were collected, and enzyme-link immunosorbent assay (ELISA) was used to monitor the antibody against to PRRSV of all the blood serum by the diagnose kit of PRRS antibody from the IDEXX company. The result shows that the average positive rate of PRRSV was 90.66% from pigs immunized by live vaccine and 75.49% from pigs immunized by inactive vaccine. The result of investigation demonstrated that Porcine reproductive and respiratory syndrome is very grievous in Shandong and attenuated vaccine is better than inactive vaccine about the effect of humoral response. In other hand, it implies that attenuated vaccine is better than inactive vaccine about the effect of immunity. 2, Identification and separation of PRRSV:One hundred and sixty-seven field samples were collected and tested with RT- PCR during the period from October in 2006 to September in 2007. The result is that one hundred and thirty-three positive samples.Symptom of these field samples is that animal heat is 40.5℃～42.0℃. Majority cases appear rubefaction, lying and hypersomnia, Most striking macroscopic lesions observed were lymph node hemorrhage or edema (100%) and diffuse interstitial pneumonia (88%), in a low proportion of samples, intestine thin-walled, kidneys hemorrhage,spleen hemorrhage and pleuritis were observed. Fifty-two PRRSV strains were isolated from positive samples which were tested in third experiment by means of increment in cells.Thereinto,23 aberrant PRRSV was tested. Investigation shows that PRRSV is one of pathogeny inducing feverish swine,but we can not judge that aberrant PRRSV was central pathogeny for this epidemic situation.3, Cloning, sequencing of ORF5-7s of PRRSV isolate: Fifty-two PRRSV strains were isolated from positive samples ,Then six PRRSV strains were selected from these ones in different area. Three pairs of primers were designed and the RT- PCR methods were developed to clone and sequence ORF3-7s of six PRRSV strains respectively .The sequences of ORF567 genes were analysed with those of LV, VR-2332,BJ-4 and CH-1a by DNA Star. Analysis indicates that six PRRSV of Shandong isolate close to VR-2332 , these and CH-1a are one sub-type. No obvious difference between aberrant PRRSV strains and PRRSV strains,but obvious difference is found among RRSV strains from difference zone.