| Pseudorabies(PR)is a widespread acute infectious disease caused by Pseudorabies virus(PRV),affecting many domestic and wild animals.It is characterized by fever,itching(except pigs),respiratory and nervous system disorders,and abortion or stillbirth of pregnant sows.The disease is prevalent in many pig farms throughout our country.To date,there is no specific medicine for treating PR,so vaccination is one of the main measures to control the occurrence and prevalence of the disease.However,vaccination is not all things.Since the late of 2011,swine pseudorabies epidemics have occurred in many areas in our country,and the succumbed animals are almost vaccinated pigs.The recurrent PRV strain emerged in this epidemic is confirmed to be a variant strain.Pigs of all ages can be infected,which seems to imply that some of the available commercial vaccines do not provide clinical protection for the currently circulating PRV variants.In this study,serological and molecular epidemiological investigations were carried out in some areas of Shandong province,China,during 2018 to 2020.We evaluated the protective efficacy of the commercial vaccine of PRV and the rPRV XJ5-gI-/gE-/TKprototype vaccine against the variant strain vPRV/XJ5 lethal challenge in growing pigs(112-day-old pigs).Then,We evaluated the inactivation effects of three disinfectants on both vPRV/XJ5 and classic PRV Ra strains at different concentrations,temperatures either in vitro or in vivo.Finally,comprehensive prevention and control measures were applicated in a large-scale pig farms,including stamping out of affected sows(gE antibody positive),optimizing immune programme,employing effective disinfectants,enhancing biosecurities,etc.The PR in this farm was eliminated,providing a sample for large scale pig farm holders to eliminate the PR caused by vPRV in China.1.Serological epidemiology investigation of porcine pseudorabiesSince late of 2011,the outbreak of PR has become a local epidemic in China.In order to monitor the PR epidemics in Shandong province,China,the PRV gE-ELISA antibody kit is employed for PRV gE antibody quarantine.In this study,a total of 19,292 sera samples collected in Shandong Provience from 2018 to 2020 were determined for PRV gE antibodies.The results suggested that the PRV gE antibody positive rate between 2018 and 2020 varied from 31.2%to 18.12%.Most of the serum samples came from sows,PRV gE antibody positive rate of these serum samples kept stable among three years.However,for serum samples from other animals of different growth periods,PRV gE antibody positive rate reached peak in 2018,and gradually went down from 2019 to 2020.2.Isolation of 4 variant PRV strains and partial genetic analysisIn 2020,97 tissue samples originated from diseased pigs was collected Shandong province,and 4 PRV variant strains were isolated from the tested samples and designated as vPRV SD1,vPRV SD2,vPRV SD3,vPRV SD4.The full gE,gC,gI and TK gene of these strains analysis showed that there was a little discrepancy between these strains and the vPRV/XJ5 strain isolated from a pig farm in Jiangsu province in 2014,and sequences of tested genes harbored high homology with those of vPRVs colltcted inland since 2012.However,sequences of tested genes from 4 vPRVs exhibited a quite diversity with those of foreign PRV strains.3.Immune protection of Bartha K61 vaccine and rPRV XJ5-gl-/gE-/TK-vaccine against vPRV/XJ5 challengeIn 2014,a variant strain of PRV from an affected pig farm in Jiangsu province was isolated in our laboratory and designated as vPRV/XJ5 strain.The variant strain was modefied to develop a rPRV XJ5-gl-/gE-/TK-prototype vaccine.The purpose of this study is to evaluate the efficacy of Bartha K61(1×106.0 TCID50 per animal)and rPRV XJ5-gI-/gE-/TK-(1×106.0 TCID50 per animal)in 12-week-old fattening pigs against lethal challenge by vPRV/XJ5 strain(4×106.0 TCID50 per animal).GB antibodies can be detected in pigs from both vaccination groups on 7 days after vaccination.After challenge,the challenge only pigs presented typical pseudorabies symptoms,and the mortality rate reached up to 100%.The vPRV/XJ5 strain was detected in all challenge only pigs from both nasal swabs and rectal swabs.Hemorrhage and congestion were found in the tonsils,brain,and lungs of dead pigs;Animals in vaccination and challenge groups did not show PR characteristic clinical symptoms after challenge,however,pigs in the vaccination/challenge groups were found virus shedding either in nasal swabs or rectal swabs.In relation to those of challenge only pigs,the duration of virus shedding was shorten and amount of shedding virus was less in animals in the vaccination/challenge groups.Furtherly,viral loads in tonsil,lung and brain from animals in the vaccination/challenge groups were also lower than those in challenge only group.We concluded that the Bartha K61 vaccine at a dose of 1×106.0 TCID50 per animal and the rPRV XJ5-gI-/gE-/TK-prototype vaccine with the same dose protected growing pigs with 100%survive rate against the lethal challenge of vPRV/XJ5 strain.Based on the outcome of the clinic score,virus shedding,viral loads in different tissues of pigs in these two groups,suggesting that either Bartha K61 vaccine or rPRV XJ5-gI-/gE-/TK-vaccine at the same dose exhibited parallel efficacy in pigs against lethal challenge with vPRV strain XJ5.These findings provide useful information for vaccination interventions and the ultimate eradication of pseudorabies caused by vPRV strains emerging in China.4.Effect of disinfectants on inactivation of both vPRV and classic PRVIn order to explore the effect of commercial disinfectants on inactivation of PRV,the disinfection experiment of the tested disinfectants on PRV was carried out both in vitro and in vivo.In this study,the vPRV/XJ5 strain and classic strain(PRV/Ra strain)of PRV were employed to evaluated the inactivation activity of three commercially available disinfectants.The concentration,reaction temperature,reaction time of disinfectants were focued.The two tested PRV strains were fully inactivated by glutaraldehyde at the concentration of 0.01%and by potassium persulfate complex at 0.025%after 25-30 min treatment at 25℃,resulting neither symptoms and deaths in mice nor cytopathic effect(CPE)in Vero cells inoculated with PRV strains treated by the tested disinfectants.Among the tested disinfectants,decyl methyl ammonium bromide exhibited poor inactivation effect on PRV strain and confirmed in Vero cells.Therefore,glutaraldehyde and potassium persulfate complex were suggested as optimal disinfectants for disinfection purpose in pig farms to inactivate the PRV contaminated in environment of pig production.5 Comprehensive prevention and control measures of pseudorabies in a large-scale pig farmFrom 2017 to 2020,continuous surveillance of PRV gE antibody in boar,gilt and sow was carried out in a large-scale pig farm in Biyang,Henan province,and gE antibody positive animals were euthanized for stamping out.Incorporating with biosafety measures,optimizing immune procedure,all pigs in this farm turned into gE negative during 2017 to 2020,and its production performance kept well.In this study,the biosafety status assessment,PRV gE antibody surveillance and gE antibody positive pig stamping out were explored.Based on PRV gB antibody surveillance quarterly in each year from 2017 to 2020,immune procedure was optimized,PRVgE antibody positive pigs were euthanized in accordance with the production plan of the farm,importantly,biosafety measures were enhanced.The comprehensive prevention and control measures for PRV in the large-scale pig farms was exploreded,leading to the elimination of PR in the farm,which provided a practical sample for PR elimination in large-scale pig farms of China. |
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