Study On The Synergistic Pathogenicity Of Co-infection Of Porcine Seneca Virus A And Pseudorabies Virus

Senecavirus A(SVA)can cause blister-like lesions in the nose and chords of pigs.When the disease is severe,the ulcers in the crown of the trotters spread to the bottom of the hoof,causing the hoof to loose or even fall off.The sick pigs have claudication.Newborn piglets(within 7 days of age)are occasionally accompanied with diarrhea symptoms,and the mortality rate is as high as 30%-70%.Pseudorabies virus(PRV)causes reproductive dysfunction in pregnant sows and neurological symptoms in newborn piglets.Morbidity and mortality in piglets are extremely high,causing huge economic losses to pig industry in worldwide.Coexistence of SVA and PRV was found in our previous epidemiological investigations,and in clinical cases,when some pigs with had recurrence of PRV,the incidence of PRV infection in pig herd with a history of SVA infection was usually more serious and more difficult to control.Therefore,a hypothesis that co-infection of SVA and PRV may lead to a synergistic pathogenic condition was speculated in this research.In order to verify this hypothesis in cellular level,a co-infection model of SVA and PRV was built using the pig kidney passage cell line(PK-15)and used to explore the effect of co-infection on virus replication ability,viral protein location and m RNA levels of cytokine.It was confirmed that SVA,with 3C protein as a most key factor,can significantly promote PRV replication.In order to evaluate the synergistic pathogenicity of co-infection of porcine seneca virus A and pseudorabies virus,35-day-old weaned pigs were used as the research model in vivo.As expected,SVA can significantly enhance the pathogenicity of PRV in weaned piglets.The detail results are as follows:1.On PK-15 cells,SVA can propagated together with PRV and its replication didn’t affected by PRV.Otherwise,load of PRV of both group C(cells were simultaneously infected with SVA and PRV)and group D(cells were infected with SVA firstly and then infected with PRV later)were significantly higher than that of group B(cells were infectedonly with PRV)in 12 hours post infection.And load of PRV in group E(cells were infected with PRV firstly and then infected with SVA later)was significantly higher than group B(cells were infected only with PRV)in 30 hours post infection.2.The IFN-β m RNA levels were significantly up-regulated by PRV and SVA in PK-15 cells,ignoring the patterns of infection or co-infection.The IFN-β m RNA levels in group A(cells were infected only with SVA)was significantly higher than that of group B(cells were infected only with PRV).The IFN-β m RNA levels in both group C(cells were simultaneously infected with SVA and PRV)and group D(cells were infected with SVA firstly and then infected with PRV later)were commensurable with that in group B(cells were infected only with PRV).And the IFN-β m RNA levels in group E(cells were infected with PRV firstly and then infected with SVA later)was commensurable with that in group B(cells were infected only with PRV).3.SVA VP1 protein or PRV g B protein was located in cytoplasm of the PK-15 cells infected with SVA or PRV alone.While in the PK-15 cells that were co-infected with SVA and PRV,SVA VP1 protein and PRV g B protein were found to partially transfer into nucleus,which differed from the PK-15 cells that was infected with SVA or PRV alone.4.Transfection with plasmid over-expressing SVA 3C protein,but not other structural proteins of SVA,into PK-15 cells significantly promoted the replication of PRV.5.Experiment results in vivo showed that co-infection of SVA and PRV didn’t affect virus shedding,the SVA shed from the 3th to the 9th day after challenge and PRV shed from the 2th to the 8th day after challenge.While the condition with typical symptoms of PRV infection,such as loss of appetite and weight,fever,circle around,collision onto the wall and formation of glial nodules in brain,in piglets that were co-infected with SVA and PRV was significantly aggravated and reached a worst peak on the 4th day after challenge,resulting in the death of 2/7 piglets.There was no death in piglets infected with PRV alone.In summary,results in vitro and in vivo indicated that SVA can promote PRV reproduction and synergies it’s pathogenic.This study provides research models and theoretical basis for exploring the synergistic pathogenesis of SVA and PRV,and also throws light on PRV vaccine development strategy.