Passive Protection Of Piglets By Maternally-derived Antibodies(MDAS) From RADV-SFV-E2-Immunized Sows And The Influence Of The MDAS On The Efficacy Of The Vaccine

Classical swine fever(CSF) is an economically important infectious disease of pigs caused by classical swine fever virus(CSFV). To facilitate the eradication of the disease in endemic areas, a marker vaccine allowing differentiation of infected from vaccinated animals(DIVA) is urgently needed. Lactogenic transfer of maternally-derived antibodies(MDAs)from immune sows is considered as an effective and economic way to provide passive protection of their piglets from CSFV infection from birth to acquisition of active immunity.It is necessary to evaluate the efficacy of a vaccine in piglets with MDAs. Previously, we have demonstrated that the DIVA vaccine rAdV-SFV-E2, an adenovirus-vectored Semliki Forest virus replicon expressing the E2 glycoprotein of CSFV, induces sterilizing immunity against lethal CSFV challenge.The aim of this study was to investigate whether MDAs from sows immunized with rAdV-SFV-E2 can effectively protect piglets against lethal CSFV challenge and vaccination with rAdV-SFV-E2 is efficacious to protect young piglets born from rAdV-SFV-E2-vaccinated sows.1. The results showed that the piglets with MDAs from the sow immunized with rAdV-SFV-E2 were protected clinically, virologically and pathologically, while the piglets with undetectable MDAs from the rAdV-SFV-E2-immunized sow were partially protected(2/4 survival), in contrast with the piglets from the non-vaccinated sow, which displayed CSF-typical clinical signs, viremia, deaths(4/4) and pathological/histopathological lesions.2. The 30 day-old piglets(n = 4) with presence or absence of MDAswere immunized with rAdV-SFV-E2 and challenged with CSFV Shimen strain. The results showed that the piglets with MDAs or not were able to induce high-level CSFV E2-specific antibodies and anti-CSFV neutralizing antibodies and did not exhibit any clinical signs.The piglets in the control group showed severe clinical signs and died at 12 days post-challenge.The results indicated that rAdV-SFV-E2 was able to confer full passive immunity to newborn piglets and the immune efficacy of rAdV-SFV-E2 was not interfered by MDAs, and completely protected the vaccinated piglets from CSFV infection.