Piglets with maternally derived antibodies from sows immunized with rAdV-SFV-E2 were completely protected against lethal CSFV challenge

• rAdV-SFV-E2 is an adenovirus-delivered, alphavirus replicon-vectored vaccine against CSF.
• Maternally derived antibodies (MDAs) from rAdV-SFV-E2-immunized sows were evaluated for passive protection.
• MDAs were detected in piglets from the sow immunized with 4 × 106 TCID50 rAdV-SFV-E2.
• Piglets with MDAs from the immunized sow were fully protected from lethal CSFV challenge.
• Piglets with undetectable MDAs from the immunized sow were partially protected.

Classical swine fever (CSF) is an economically important infectious disease of pigs caused by Classical swine fever virus (CSFV). To facilitate the eradication of CSF in endemic areas, a marker vaccine enabling differentiation of infected from vaccinated animals (DIVA) is urgently needed. 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 complete protection from lethal CSFV challenge. The aim of this study was to investigate whether maternally derived antibodies (MDAs) from sows immunized with rAdV-SFV-E2 can effectively protect piglets against lethal CSFV challenge. Three groups of five-week-old piglets (n = 4), with or without MDAs, were challenged with the highly virulent CSFV Shimen strain. Clinical signs, CSFV-specific antibodies, viremia and pathological and histopathological changes were monitored. 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. These results indicate that MDAs from the sow immunized with rAdV-SFV-E2 are able to confer full passive immunity to newborn piglets.