Thirty-seven specimens of wild boar sera were collected from August 2016 to March 2018 in Ishikawa prefecture, Japan. Thirty-two specimens (86.5%) were positive for neutralizing antibodies against Japanese encephalitis virus (JEV). Eight specimens (21.6%) were positive for IgM antibodies against JEV. One sample was obtained from a wild boar captured in February during the winter season. Four other serum specimens obtained during the winter season were positive using a JEV gene-specific PCR assay. Based on IgM and PCR assays, wild boars were infected with JEV during the winter season, suggesting that the prevalence of JEV antibodies in wild boars in Ishikawa is high and JEV activity is possible during winter in this region. In addition, wild boars may play an important role in the infection cycle of JEV.

CcJE+Advax is an inactivated cell culture Japanese encephalitis (JE) vaccine formulated with Advax, a novel polysaccharide adjuvant based on delta inulin. This vaccine has previously shown promise in murine and equine studies and the current study sought to better understand its mechanism of action and assess the feasibility of single dose vaccine protection. Mice immunised with ccJE+Advax had higher serum neutralisation titres than those immunised with ccJE alone or with alum adjuvant. ccJE+Advax induced extraordinarily broad cross-neutralising antibodies against multiple flaviviruses including West Nile virus (WNV), Murray Valley encephalitis virus (MVEV), St Louis encephalitis virus (SLEV) and Dengue virus-1 and -2 (DENV-1 and -2). Notably, the DENV-2 cross-neutralising antibodies from ccJE+Advax immunised mice uniquely had no DENV-2 antibody-dependent infection enhancement (ADIE) activity, in contrast to high ADIE activity seen with DENV-1 cross-reactive antibodies induced by mbJE or ccJE alone or with alum adjuvant. JEV-stimulated splenocytes from ccJE+Advax immunised mice showed increased IL-17 and IFN-γ production, consistent with a mixed Th1 and Th17 response, whereas ccJE-alum was associated with production of mainly Th2 cytokines. In a mouse lethal challenge study against highly virulent JaTH160 JEV strain, ccJE+Advax conferred complete protection in a two-dose schedule with 50 ng of vaccine antigen and near complete protection after a single 200 ng dose of vaccine antigen. There is an ongoing lack of human vaccines against particular flaviviruses, including WNV, SLEV and MVEV. Given its ability to provide single-dose JEV protection and induce broadly neutralising antibodies devoid of ADIE activity, ccJE+Advax vaccine could be useful in situations where rapid protection is desirable, e.g., during a local outbreak or for use in travellers or armies requiring rapid deployment to JEV endemic regions.

Hepatitis E virus (HEV) is a zoonotic pathogen with multiple hosts, posing significant public health risks, especially in regions like Japan where game meat consumption is prevalent. This study investigated HEV infection and viral shedding in wild boars, sika deer, and Japanese serows across Japan. A total of 1896 serum samples were tested for anti-HEV antibodies, 1034 for HEV RNA, and 473 fecal samples for viral shedding. Anti-HEV antibodies were detected in wild boars from all seven prefectures studied, while HEV RNA was detected in wild boars from Fukuoka, Oita, and Miyazaki in southern Japan, as well as Yamaguchi prefecture. Genetic analysis revealed subtypes 3b, 4a, and 4g, with 3b being the most prevalent. Subtype 3b exhibited distinct geographical clustering, whereas 4g persisted exclusively in Yamaguchi for over 12 years. Infectious HEV particles were confirmed in wild boar feces, highlighting the risk of environmental contamination and zoonotic transmission. Sika deer showed no evidence of HEV infection, and only one Japanese serow tested positive for antibodies without detectable RNA. These findings underscore the importance of ongoing surveillance to assess the zoonotic risks from game meat consumption and prevention of HEV transmission to humans.

In July 2018, acute Q fever (AQF) was diagnosed in two Japanese individuals from the same family. They returned to Japan from Malawi, where the epidemiology of AQF is unknown. A child presented to the hospital with high-grade fever without any symptoms, and a mother presented with fever and dry cough. Paired serum antiphase Ⅱ IgM and IgG significantly elevated in the convalescent phase in both cases. Coxiella burnetii gene (IS1111) was detected from the mother’s blood sample. They had no reported direct animal contact, but the onset of symptoms coincided with the dry season in Malawi, which may have facilitated environmental dispersal. These cases may serve as an alert for high-risk people to possible AQF spread and underdiagnosis in Malawi.

Japanese encephalitis virus (JEV) has a positive-sense single-stranded RNA genome and belongs to the genus Flavivirus of the family Flaviviridae. Persistent JEV infection was previously shown in pig blood cells, which act as a natural reservoir of this virus. We aimed to determine the pathogenicity factors involved in persistent JEV infection by analyzing the pathogenicity and genome sequences of a virus isolated from a persistent infection model. We established persistent JEV infections in cells by inoculating mouse fetus primary cell cultures with the Beijing-1 strain of JEV and then performing repeated infected cell passages, harvesting viruses after each passage while monitoring the plaque size over 100 generations. The virus growth rate was compared among Vero, C6/36, and Neuro-2a cells. The pathogenicity was examined in female ICR mice at several ages. Additionally, we determined the whole-genome sequences. The 134th Beijing-1-derived persistent virus (ME134) grew in Vero cells at a similar rate to the parent strain but did not grow well in C6/36 or Neuro-2a cells. No differences were observed in pathogenicity after intracerebral inoculation in mice of different ages, but the survival time was extended in older mice. Mutations in the persistent virus genomes were found across all regions but were mainly focused in the NS3, NS4b, and 3′NCR regions, with a 34-base-pair deletion found in the variable region. The short deletion in the 3′NCR region appeared to be responsible for the reduced pathogenicity and growth efficiency.