A noval strategy of deletion in PK gene for construction of a vaccine candidate with exellent safety and complete protection efficiency against high virulent Chinese pseudorabies virus variant

Abstract

A variant of pseudorabies virus (PRV) with enhanced pathogenicity have emerged in many vaccinated swine herds in China since 2011. PRVΔTK&gE-AH02, a previously described TK/gE deletion PRV strain arising from the PRV variant AH02LA, has been shown to be safe for PRV antibody positive piglets, and could provide protection against emerging PRV variants. However, inoculation of PRVΔTK&gE-AH02 into PRV antibody negative neonatal piglets caused lethal infection. In the study, in order to attenuate the virulence of PRVΔTK&gE-AH02, an additional deletion of 1∼x223C13 bp of US3 (the serine/threonine kinase, PK) gene was performed to generate a TK/PK/gE deletion PRV variant (PRVΔTK&PK&gE-AH02). We found that the growth kinetics of PRVΔTK&PK&gE-AH02 was similar to that of PRVΔTK&gE-AH02. Mice inoculated with PRVΔTK&PK&gE-AH02 in different dose (104.0∼x223C107.0 TCID50) survived and showed no observable clinical symptoms. No virus was detected in the brains or lungs of the mice inoculated with PRVΔTK&PK&gE-AH02. Moreover, mice inoculated with PRVΔTK&PK&gE-AH02 and PRVΔTK&gE-AH02 showed similar survival against virulent PRV AH02LA strain. Importantly, safety test showed no clinical symptoms in PRV antibody negative neonatal piglets that were intranasally inoculated with PRVΔTK&PK&gE-AH02 at a dose of 106.5 TCID50, indicating that the virulence of PRVΔTK&PK&gE-AH02 was significantly mitigated. Piglets immunized with PRVΔTK&PK&gE-AH02 exhibited a high serum neutralization index. All piglets inoculated intramuscularly (I.M.) with 1 mL (105.0 TCID50) PRVΔTK&PK&gE-AH02 were completely protected against challenge intranasally (I.N.) with 2LD50 (106.5TCID50) PRV AH02LA strain. In summary, our results indicate that deletion of 1∼x223C13 bp of US3 (PK) can provide a useful way for further attenuation of PRV and the PRVΔTK&PK&gE-AH02 might be a promising vaccine candidate for controlling of the virulent PRV variants in China.