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Emergency vaccination alleviates HP-PRRS virus infection

Research carried out at a university in Yangling, close to Xi’an, China indicate that emergency vaccination can effectively alleviate highly pathogenic Porcine Reproductive & Respiratory Syndrome (HP-PRRS) infection. HP-PRRS was first detected in 2006 and has ever since created massive losses in both China and Vietnam.

The goal of the trial was to assess the effect of emergency vaccination on the reduction of contact-induced infection and pathological damage caused by the HP-PRRS virus.

In a contact exposure experiment, 20 pigs were equally divided into four groups. Groups 1, 2 and 3 were housed in one unit, whereas Group 4 was separately housed. Group 1 was challenged with HP-PRRS virus on day 0. Group 2 and 4 did not receive treatment and were used as the contact-infected and uninfected controls, respectively. Group 3 was treated with the attenuated vaccine at 0 days post-inoculation. The rectal temperatures, clinical signs, pathologic lesions and viraemia of the piglets were detected and evaluated.

The vaccinated pigs in Group 3 showed less clinical morbidity, viraemia, temperature fluctuations and lung lesions at 14 days post-inoculation, as compared with the contact-infected (Group 2) and experimentally infected (Group 1) pigs. Higher serum IFN-γ levels were detected among the pigs that received emergency immunisation. Thus, IFN-γ may be involved in immunity against HP-PRRS virus infection.

As one of the reasons for their research, the researchers pointed to an inconsistency in control of HP-PRRSV using the attenuated vaccine of a modified-live virus (MLV) derived from the American PRRSV VR-2332. They explain: “It has been widely used in PRRSV-prevalent countries, with its safety and effectiveness proven by previous studies. However, clinical observations showed that several MLV-vaccinated farms in China suffered from heavy economic losses caused by HP-PRRS virus in 2006 to 2010. This inconsistency revealed that the MLV vaccine provides limited protection from HP-PRRS virus under normal immunisation procedures.”

They continued: “Several farms in Jiangsu, China successfully reduced HP-PRRS virus damage using a promising emergency immunisation strategy with the MLV strain. An excess dose of the MLV vaccine (four to six doses) was administered upon confirmation of HP-PRRS virus infection. Losses were reduced by 30% to 70%, as compared with the untreated herds. Vaccine intervention against typical PRRS virus has been previously studied. Although not as effective as a cure, vaccine intervention could reduce the persistence and transmission of PRRS virus in a pig population infected with the heterogonous isolates.”
The research was carried out by Xiao Li, Li Qiu, Zengqi Yang, Ruiyi Dang and Xinglong Wang, all attached to the Northwest A&F University in Yangling. They stated: “Our findings provide a novel and useful strategy for controlling clinical HP-PRRS virus.”
The article was published in BMC Veterinary Research, earlier this year.

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