Oral administration of recombinant Lactococcus lactis co-expressing fusion VP1 protein of duck hepatitis a virus type 1 and 3 protects ducklings against infection

Duck viral hepatitis (DVH) is one of the most common diseases of waterfowl. Duck hepatitis A virus type 1 (DHAV-1) and type 3 (DHAV-3) have been on the rise seriously endangering the development of duck farming. In this study, we constructed a recombinant Lactococcus lactis (L. lactis) co-expressing the fusion VP1 protein of DHAV-1 and DHAV-3. Western blot and immunofluorescence analyses confirmed that the fusion VP1 protein was expressed on the cell surface of recombinant L. lactis stain. After immunization with the recombinant L. lactis by oral administration, the ducklings were challenged with highly pathogenic DHAV-1 and DHAV-3 by natural infection. The results showed that the recombinant L. lactis induced the specific IgG antibodies, and significantly increased the level of mucosal secretory immunoglobulin A (sIgA) and cytokines, such as interleukin-4 (IL-4), interleukin-10 (IL-10), and interferon gamma (IFN-γ). The immunized ducklings delayed death for around 4 days, and reduced mortality with the relative percent survival (RPS) being 64.71 %, 61.54 % and 57.89 % in DHAV-1, DHAV-3 and DHAV-1 + 3 infection group respectively. These results showed that the recombinant L. lactis constructed in this study provides a promising candidate for prevention and control of DHAV-1 and DHAV-3 infection.