Epidemiological Investigation Of Highly Pathogenic Porcine Reproductive And Respiratory Syndrome And Trial Of Live Vaccine In Tianjin

Porcine reproductive and respiratory syndrome(PRRS), as one of the most devastating acute infectious diseases in the swine industry, is characterized by reproductive disorders in pregnant sows and respiratory symptoms in piglets. In the late 1980 s, PRRS emerged in both North America and Europe, and quickly spread and prevailed throughout the world, arousing high attention from the international community. In 2006, a swine “high fever” disease induced by a virulence-enhanced variant strain of porcine reproductive and respiratory syndrome virus(PRRSV) first emerged in China, the clinical manifestations, morbidity and mortality of which are severer than those of classical PPRS. Later, it spread to such Southeast Asian countries as Vietnam and Laos, causing immense economic losses in the swine industry in these countries. In 2008, China revised the List of Categories I, II and III Animal Epidemic Diseases; the updated version has included highly pathogenic PRRS(HP-PRRS) into Category I animal epidemics and classical PRRS into Category II animal epidemics.Swine are the only known natural host of PRRSV. PPRS can infect pigs of different ages and breeds. Infected pigs excrete the virus in their saliva, feces, urine, semen, milk, etc.. PRRSV is mainly transmitted by direct or indirect contact, and it can also be transmitted vertically. In order to make clear the epidemiological profile of HP-PRRS in Tianjin, during April 2012 to June 2014, the RT-PCR method was used to detect PRRS viral nucleic acid in 245 suspected tissue samples and 3,086 pig serum samples collected from 12 districts(counties). Among them, 222 tissue samples and 46 serum samples were found positive. Meanwhile, ELISA, an antibody assay method, was used for serological and epidemiological investigation of 12,645 samples collected from different districts and countries. Among the 948 pigs(not vaccinated with HP-PRRSV vaccine) serum samples, 395 were found to be PRRSV antibody-positive; among the 11,697 pigs(vaccinated with HP-PRRSV vaccine) serum samples, 10,186 were found to be antibody-positive. Results showed that the detection rate of suspected HP-PRRS tissue samples from different districts and counties of Tianjin was relatively high during April 2012 to June 2014, and a part of normal pigs in inventory also carried the virus, suggesting an epidemic trend of this disease in Tianjin.The prevention and control of PRRS mainly relies on good biosafety management and comprehensive prevention and control measures. Also, since vaccination can effectively reduce the morbidity and mortality of the disease, it can be used as an effective measure for stabilizing and controlling the epidemic situation. There are several factors that can affect the protective effect after vaccination with PRRSV vaccine. A vaccine strain which is the same as or closely related to the epidemic strain can effectively stimulate the organism to generate immune responses, thus providing the best immune effect. The post-immunization antibody levels serve as an important indicator for evaluating the immune effect. High levels of antibodies(neutralizing antibodies) can effectively prevent the transmission of PRRSV while neutralizing the virus in the body. Various types of vaccines, such as attenuated, inactivated and genetic engineering vaccines, have been used for prevention and control of PRRS in succession, among which attenuated and inactivated vaccines are most widely used. Attenuated vaccines can effectively stimulate the organism to generate immune responses, produce high levels of neutralizing antibodies and cellular immunity, and effectively resist infection by wild-type viruses homologous or closely related to PRRSV. At present, main commercialized vaccines available on the market are the conventional attenuated and inactivated vaccines. In China, since the American type PRRSV strain is the prevalent one, vaccines used are dominated by American type inactivated and attenuated vaccines. Classical strain vaccines mainly include attenuated PRRSV vaccine(CH-1R), and main HP-PRRSV vaccines are JXA1, Hu N4-F112, TJM-F92, etc..During September to December, 2014, the clinical efficacy of a live HP-PRRSV vaccine(TJM-F92) provided by a biotechnology company in Xinjiang was tested on a swine farm in Tianjin. The safety of the trial vaccine was verified by observation of changes in pigs’ body temperature, mental state and food intake, and the immune effect of the vaccine was evaluated by antibody assay. Results showed that vaccination with this vaccine could well stimulate the organism to generate immune responses and also improve the uniformity of the herd antibody levels.