Comparasion Of Pathogenicity Of Different Porcine Reproductive And Respiratory Syndrome Virus Isolates In Piglets And Preparation Of Inactivated Vaccine

Porcine reproductive and respiratory syndrome (PRRS),first recognised in the USA in 1987, is characterised by respiratory disease in young pigs and severe reproductive failure in sows, includeing abortion, stillbirths and weak piglets. The virus has spread widely in China and considerable pathogenicity variation has been identified from different regions. Since June 2006 ,herds of pigs in the Mid-Eastern region of China have experienced recent outbreaks of a severe form of porcine reproductive and respiratory syndrome (PRRS) characterised by high fever and morbidity and mortality in animals of different ages. Here, we isolated a new strain of PRRSV with high pathogenicity. Even though several PRRSV vaccines are available, control of the disease remains difficult.In order to evaluate the different pathogenicity between the strain SY0608 (the latest isolated strain of PRRSV) and the traditional strain S1, 30 days old post-weaning piglets were separated into 3 groups randomly and infected with these two kinds of virus respectively (5 infected with S1 strain and 4 infected with SY strain,2 used as empty control). After challenge the clinical signs, pathological, etiology and serology were examined for two weeks .The results showed that the pigs in the PRRSV SY0608 strain group had cause severe clinical signs, increased rectal temperature up to 41.8℃rapidly,and showed a dramatic decrease in white blood cell and severe pathological consequences. Mean while a significantly high level of viremia and viral load in tissues in the group of SY0608 was maintained more highly and extensively compared to those in S1 group.In addition ,SY0608 infection group produced a higher level ELISA antibody response than the S1 strain. It showed that Virulent PRRSV SY0608 had a markedly stronger pathogenicity than strain S1.Two different inactivated vaccines of PRRSV were made with strain SY0608 (the latest isolated strain of PRRSV) . Piglets were randomly divided into three groups, one group was served as challege control ,the other two groups were vaccinated with PRRSV inactivated vaccine, PRRSV-lipopolysaccharide inactivated vaccine, respectively. After 21 days post immuniziation, each pig was challenged with virulent strain of PRRSV SY0608. The results indicated that the pigs in the control group and PRRSV-inactivated vaccine group all had severe clinical signs and severe pathological consequences. But pigs in the PRRSV-lipopolysaccharide inactivated vaccine group had a lower level of clinical signs and pathological consequences comparised with those in other grouus.There was no significantly high level of viraemia period and viral load in tissues between the groups.It indicated that PRRSV-lipopolysaccharide inactivated vaccine could provide higher protective efficiency than the usually PRRSV inactivated vaccine. The bacterial lipopolysaccharide could be used as adjuvant to improve the effect of PRRSV inactivated vaccine. PRRSV- lipopolysaccharide inactivated vaccine might take parts of role in preventing and control of highly pathogenic PRRSV infection in pigs.