Epidemiological Investigation And Genetiv Variation Of Porcine Reproductive And Respiratory Syndrome Virus In Shandong

Porcine high fever disease(PHFD) occurred in some medium-scale or scattered pig farms in Shandong area during 2008-2010. This recent epidemic disease resulted in a high morbidity and mortality of all the pig herds, different from the disease which mainly infected piglets and nursery pigs occurred during 2006-2007. For the sake of learning the data of porcine reproductive and respiratory syndrome (PRRS) in Shandong area, serology and pathology of PRRS were conducted in this study, which is able to provide important evidence for the prevention and control the disease in this area.The studies included five aspects as follows.1. Serological investigation of PRRS in Shandong province during 2008-2010 was carried out by enzyme-link immunosorbent assay(ELISA). The positive rate of PRRS antibody was 50.7% (139/274) in non-vaccinated pigs, indicating that PRRS is prevalent in Shandong pig farms before using commercial vaccines. The positive rate of PRRS antibody was 69.9% (826/1182) in pigs immunized with inactivated PRRS vaccine, and 87.1% (498/572) in pigs injected with attenuated PRRS vaccine, which indicated different types of vaccines can provide various protective effects to pigs in the clinical practice.2. A total of 212 samples were collected from 14 areas of Shandong province during 2008-2010 and analysed by a multiplex polymerase chain reaction (M-PCR). The positive rates of highly pathogenic PRRSV (HP-PRRSV) and CSFV were 57.1% (121/212) and 29.2% ( 62/212), respectively. The mixed infection rate of PRRSV and CSFV was 11.8% (25/212). The results showed that HP-PRRSV is one of etiological agents of PHFD.3. Sixteen PRRSV strains were isolated from PCR-positive samples, and they can induce cytopathic effect (CPE) in Marc-145 cell. Artificial infection tests using SX-1 strain, a representative HP-PRRSV isolate, showed that SX-1 strain can cause typical clinical syndromes alike those of PHFD. 4. All of Sixteen HP-PRRSV isolates exhibited 30-amino-acid discontiguous deletions in the hypervariable region of Nsp2, but the Nsp2 sequence of these isolates was incompletely identical. The Nsp2 of these isolates shared high nucleotide homologies and amino acid homologies with that of PRRSV variant strains reported in China during 2006-2007. 16 PRRSV isolates exhibited a few mutations but no deletion in ORF5. A hypervariable region was found at positions 26-39aa of GP5 protein.5. The complete genome sequences of SX-1, ZP-1 and JN-2 isolates were obtained in the present study. The genomes of the three isolates all included 15320 nucleotides (not including polyA sequences). A large number of variations mainly occurred in the Nsp2, ORF3 and ORF5, while ORF6 and ORF7 were relatively conservative.