The Safety And Clinical Immune Effect Of Live Vaccine Of Porcine Respiratory And Reproductive Syndrome (r98 Strain)

Porcine respiratory and reproductive syndrome (PRRS) is one of the most economically significant diseases of swine, which is characterized by abortions in sows, premature farrowing, stillborn pigs and respiratory disease. The current commercial PRRSV vaccines mainly include modified live vaccine and inactivated vaccine, but only the latter is available in our country. To develop a safe and effective live vaccine for PRRS, the safety and clinical immune effect of R98 live vaccine of PRRSV were systemically investigated in pigs in this study.1. Safety test for the vaccineInoculation of 7 days-old piglets in different routes by one time: twelve 7-day-old suckling pigs were separated into three groups of four animals each. Vaccination was given as follows: group 1 received 10^5.0 TCID₅₀/ml intramuscularly; group 2 received 10^5.0 TCID₅₀/ml intranasally; group 3 received 1 ml media only as negative control. All experimental animals were bred 30 days separately. It was showed that there were no abnormal responses among all inoculated animals with different routes, and there was no significant difference in weight between experimental pigs and control. The results of detecting PRRSV in nasal scraping by RT-PCR, showed that viruses in experimental animals with two different routes were positive within one and two weeks, negative within three and four weeks, and negative in control animals.Inoculation of piglets by two times: ten 14-day-old piglets were separated into two experimental groups of five animals each. Vaccination was given intramuscularly as follows: group 1 received 10^5.0 TCID₅₀/ml and boosted 2 weeks post-priming; group 2 received 1 ml media only as negative control following the same vaccination protocol. All experimental animals were bred 30 days separately. It was showed that there were no abnormal responses in all inoculated animals, and there was no significant difference in weight between experimental piglets and control. The results of detecting PRRSV in nasal scraping by RT-PCR, were same with the above.Inoculation of piglets by one time with super-dose: ten 14-day-old piglets were separated into two experimental groups of five animals each. Vaccination was given intramuscularly as follows: group 1 received 10^6.0 TCID₅₀/ml; group 2 received 1 ml media only as negative control following the same vaccination protocol. All experimental animals were bred 30 days separately. The results showed that there were no abnormal responses in all inoculated animals, and there was no difference in weight between experimental piglets and control. The results for detecting PRRSV in nasal scraping by RT-PCR, were same with the above.Inoculation of premature sows: ten premature sows were separated into two experimental groups of five animals each. Vaccination was given intramuscularly as follows: group 1 received 2×10^6.0 TCID₅₀/ml; group 2 received 2 ml media only as negative control following the same vaccination protocol. All experimental animals were bred separately and observed until impregnation and parturition. The results showed that there were no abnormal responses in all inoculated animals, and there were no reproductive failure such as premature farrowing, stillborn pigs, etc.Inoculation of pregnant sows: six pregnant sows of 90-day, were separated into two experimental groups of three animals each. Vaccination was given by injection intramuscularly as follows: group 1 received 2×10^6.0 TCID₅₀/ml; group 2 received 2 ml media alone as negative control following the same vaccination protocol. All experimental animals were bred separately and observed until parturition. The results showed that there were no abnormal responses in all inoculated animals, and there were no reproductive failure such as premature farrowing, stillborn pigs, mummification, etc.Effect of PRRSV vaccine on the vaccination of CSF vaccine in piglets: twelve 14-day-old piglets were separated into three experimental groups of four animals each. Vaccination was given intramuscularly as follows: group 1 received 10^5.0 TCID₅₀/ml and followed by fold doses CSF vaccine 2 weeks post-priming; group 2 received 1 ml media alone and followed by two doses CSF vaccine 2 weeks post-priming; group 3 received 1 ml media alone as negative control. All experimental animals were bred 30 days separately. The sera titers of CSF were detected by indirect HI test. The results showed the sera titers of two groups with CSF vaccine were similar.2. The clinical immune effect of the vaccineThe field experiments of pigs were done in farms of Huaian, Yancheng, Suzhou of Jiangsu province using the five batches of PRRS (R98 strain) products that were produced by Ruipu (Baoding) bio-medical LTD. The results showed that there were no abnormal responses in experimental animals. Antibodies against PRRSV were positive. The incidence of diseases of piglets decreased, and the ratio of survival was increased to over 90 percent. The ratio of stillborns and nonpregnancy decreased by over 50 percent.These results showed that the R98 strain live vaccine is safe for the pigs over 7-day-old and pregnant sows. The piglets excreted virus only in two weeks post-inoculation. The vaccine has no effect on the immune function of pigs and had no side effect.