The Protective effects of a live-attenuated genotype I Japanese Encephalitis Vaccine in mice and boars

1. SD12-F120 induces high levels of neutralizing antibodies in both mice and boars. 2. SD12-F120 effectively preventing JEV-induced orchitis in boars. 3. SD12-F120 offers complete protection against genotype I JEV virulent, which is a promising live-attenuated vaccine candidate of GI JEV. Japanese encephalitis (JE) is a zoonotic mosquito-borne viral disease caused by the Japanese encephalitis virus (JEV). The virus is transmitted among adult pigs, causing abortion in sows and orchitis in boars. Vaccination remains the most effective strategy for the prevention and control of this disease. Studies have shown that genotype I (GI) JEV has replaced GIII JEV as the dominant strain in many Asian countries. However, all currently licensed JE vaccines, including the widely used SA14-14-2 live attenuated vaccine, are derived from the GIII strain. It has been reported that GIII-based vaccines do not provide complete protection against the GI strain. In this study, we conducted vaccination-challenge protection assays in mice and boars to evaluate the protective efficacy of live attenuated GI (SD12-F120) derived vaccines against challenge by a homologous genotype. In mice, immunisation with the vaccine induced a potent viral-neutralising response against the homologous GI JEV SD12 strain. The SD12-F120 vaccine provided complete protection against lethal challenge by SD12, whilst also attenuating viraemia. JEV was not detected in the blood, oronasal swabs, or testicles of boars receiving the SD12-F120 vaccine. Vaccination induced high levels of neutralising antibodies against the homologous GI strain in boars, with titers as high as 64. Histopathological analysis showed that interstitial cells of the boar testis and spermatogonia at all levels were well preserved in the vaccine-immunised group, effectively suppressing the occurrence of orchitis. These results showed that the SD12-F120 vaccine provides boars complete protection against challenge by SD12, whilst also protecting against viraemia and testicular damage. Our findings indicate that SD12-F120 is a promising live-attenuated vaccine candidate for controlling the spread of GI JEV.