| Porcine reproductive and respiratory syndrome (PRRS) is one of the important infectious diseases, its main characteristics are productive failure in sows and respiratory signs in piglets, has spread to most parts of the world. It has brought huge economic losses to the world pig industry. Since June 2006,the outbreak of highly pathogenic porcine reproductive and respiratory syndrome in China causing serious economic losses has become one of the most important epidemics endangering Chinese pig industry.In order to find a efficient method to control the epidemic period of PRRS, four farms (A, B, C,D) suspected infected by PRRSV were chosen to control PRRSV using in different methods. The experimental boar group of A and B were inoculated with sera from infected pigs to let other pigs obtained virus infections simultaneously and produce maternal antibodies to protect piglets, combining with all-in and all-out raising method, which can shorten viremia time obviously and end plague fast. Group A were infected simultaneously with sera from infected pigs and group B were divided into two batches to infect with sera from infected pigs. To test the effectiveness of this method, group C were used as vaccine immunized group and group D as control group. The results showed that, in group A artificial infected with wild virus, abortion rate and mortality of sows are 8.7% and 3.1% respectively in 4 weeks and then stabilized; the mortality of piglets is decrease from 84.5% to 68.5% in two month and then stabilized. In group B artificial infected with wild virus, abortion rate and mortality of sows are 9.3% and 1.35% respectively in 4 weeks and then stabilized. Since PRRS had occurred before artificial infection, the mortality of suckling piglet amount to 40% in several batches piglets (Sows not infected by sera). After artificial infection, the mortality of suckling piglets in five delivery room are 22.5%,8.2%,15%, 11.9% and 5.7% respectively, the results is very obvious compared with out artificial infection. The mortality of second batches piglets from delivery to market was below 10% and restored normal production. In group C, abortion rate and mortality were decreased from 7.4% and 2.8% at the time of immunization to 2.8% and 0.3% after 2 month, but abortion rate was still kept at 2% at very month and can not restore normal production. In group D, the abortion rate and mortality of sows did not decreased obviously in 6 month and abortion rate was kept above 2% and the mortality of piglets is above 30% in every month. Not another measures were adopted, until the farm restored normal production after 2 month.In order to test whether artificial infection is success or not, two test experiments were carried out in group A and B. The antibody variation and homology of ORF5 were detected in 3 weeks before and after infection, the level of antibody was increased and homogeneity and 3 virus strains were isolated. The homology between three isolated virus and inoculated virus is above 98.1%, which proved the infection is success. In group C, antibody was increased obviously and 4 virus strains were isolated, the homology between four isolated virus and BI vaccine is from 87.9% to 88.1%. Combining with antibody and production data, this immunization is valid. Group C, through pathogen detection, was proved to be infected by variant strain of PRRSV.From detection results and production data, we can make a conclusion that PRRSV outbreak can be controlled by immunization by sera isolated from infected pigs. Especially, group B, which was divided into two batches and inoculated by sera, caused economic loss is not larger than natural PRRSV infection, which may be used as an effective method to control PRRSV. |
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