Satoshi Taniguchi

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), the causative agent of the global coronavirus disease 2019 (COVID-19) pandemic, frequently induces olfactory dysfunction (OD), a symptom that significantly impacts patients' quality of life. Understanding the variability in OD and nasal tissue pathology across different SARS-CoV-2 variants may provide insights as to the mechanisms underlying this symptom and inform therapeutic strategies for COVID-19-related sequelae. This study examines the OD and associated nasal pathology in Syrian hamsters infected with SARS-CoV-2 variants, including Wuhan (WA-1), Alpha, Beta, Gamma, Delta, and Omicron, at 5 days post-infection. Olfactory function was assessed using buried food detection tests. Hamsters infected with the WA-1, Alpha, Beta, and Gamma variants exhibited prolonged discovery times as compared to controls, indicating severe OD. In contrast, those infected with the Delta and Omicron variants showed minimal or mild delays. Pathological examination of the lateral turbinate (LT) revealed severe olfactory epithelial damage in WA-1, Alpha, Beta, Gamma, and Delta variant infections, while the Omicron variant caused minimal damage. Viral antigens were detected in retained and/or sloughed epithelial cells in the LT across all variant infections. These results demonstrate significant differences in OD severity and nasal tissue damage among SARS-CoV-2 variants, providing critical insights for understanding the pathogenesis of this symptom and guiding treatment development for COVID-19 sequelae. IMPORTANCE: Olfactory dysfunction (OD) is a prominent and distinctive symptom of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection that significantly affects patients' quality of life. This study reveals that Syrian hamsters infected with different SARS-CoV-2 variants (WA-1, Alpha, Beta, Gamma, Delta, and Omicron) exhibit varying degrees of OD and nasal tissue pathology. Hamsters infected with the WA-1, Alpha, Beta, and Gamma variants experienced significant OD, while those infected with Delta and Omicron showed milder symptoms. Severe epithelial damage in the nasal turbinate was observed in hamsters infected with WA-1, Alpha, Beta, Gamma, and Delta variants, whereas Omicron variant infection resulted in minimal tissue injury. Despite the variability in OD and tissue damage, viral antigen was detected in all infected hamsters. These findings underscore the diverse impact of SARS-CoV-2 variants on olfactory function and nasal tissue pathology, providing important insights into the pathogenesis of OD and guiding potential therapeutic strategies for coronavirus disease 2019-related olfactory sequelae.

Lassa virus (LASV) is the causative agent of Lassa fever (LF), a severe hemorrhagic disease with potential for lethal outcomes. Classified as a risk group 4 pathogen, it represents a significant public health threat in endemic regions. Our laboratory previously developed a novel lethal guinea pig model of Lassa fever using the clinical isolate LASV strain LF2384. However, the specific pathogenic factors underlying LF2384 infection in guinea pigs remained unclear. In this study, we aimed to investigate the immunological differences elicited by LF2384 and LF2350, another LASV strain isolated from a nonlethal case within the same outbreak. We compared the expression kinetics of key immune-related genes in guinea pigs infected with either LF2384 or LF2350. Using reverse genetics, we identified the L protein as a critical viral factor responsible for the observed pathogenic differences between the strains.

Guanarito virus (GTOV) is a rodent-borne virus. GTOV causes fever, prostration, headache, arthralgia, cough, sore throat, nausea, vomiting, diarrhea, epistaxis, bleeding gums, menorrhagia, and melena in humans. The lethality rate is 23.1% or higher. Vero cell-adapted GTOV S-26764 shows a clear cytopathic effect (CPE), whereas the parental virus shows unclear CPE in Vero cells. We generated a reverse genetics system to rescue recombinant GTOVs and found that E1497K in the L protein was responsible for the formation of clear plaques as well as enhanced viral RNA replication and transcription efficiency. This reverse genetic system will accelerate vaccine and antiviral drug developments, and the findings of this study contribute to the understanding of the function of GTOV L as an RNA polymerase.

Lujo virus (LUJV), which belongs to Mammarenavirus, family arenaviridae , has emerged as pathogen causing severe hemorrhage fever with high mortality. Currently, there are no effective treatments for arenaviruses, including LUJV. Here, we screened chemical compound libraries of Food and Drug Administration (FDA)-approved drug and G protein-coupled receptor-associated drugs to identify effective antivirals against LUJV targeting cell entry using a vesicular stomatitis virus-based pseudotyped virus bearing the LUJV envelope glycoprotein (GP). Cannabinoid receptor 1 (CB1) antagonists, such as rimonabant, AM251 and AM281, have been identified as robust inhibitors of LUJV entry. The IC ₅₀ of rimonabant was 0.26 and 0.53 μM in Vero and Huh7 cells, respectively. Analysis of the cell fusion activity of the LUJV GP in the presence of CB1 inhibitors revealed that these inhibitors suppressed the fusion activity of the LUJV GP. Moreover, rimonabant, AM251 and AM281 reduced the infectivity of authentic LUJV in vitro, suggesting that the antiviral activity of CB1 antagonists against LUJV is mediated, at least in part, by inhibition of the viral entry, especially, membrane fusion. These findings suggest promising candidates for developing new therapies against LUJV infections. Importance: To investigate antiviral drugs against Lujo virus (LUJV), we screened chemical compound libraries to identify effective antivirals against LUJV entry. CB1 antagonists were identified as robust inhibitors of LUJV entry. The cell fusion activity of LUJV GP was suppressed by CB1 inhibitors. Furthermore, CB1 antagonists reduced the infectivity of authentic LUJV. These findings suggest promising candidates for developing new therapies against LUJV infections.

The viral family Arenaviridae contains several members that cause severe, and often lethal, diseases in humans. Several highly pathogenic arenaviruses are classified as Risk Group 4 agents and must be handled in the highest biological containment facility, biosafety level-4 (BSL-4). Vaccines and treatments are very limited for these pathogens. The development of vaccines is crucial for the establishment of countermeasures against highly pathogenic arenavirus infections. While several vaccine candidates have been investigated, there are currently no approved vaccines for arenavirus infection except for Candid#1, a live-attenuated Junin virus vaccine only licensed in Argentina. Current platforms under investigation for use include live-attenuated vaccines, recombinant virus-based vaccines, and recombinant proteins. We summarize here the recent updates of vaccine candidates against arenavirus infections.

Heartland bandavirus (HRTV) is an emerging tick-borne virus that is distributed in the United States and that causes febrile illness with thrombocytopenia and leukocytopenia. It is genetically close to Dabie bandavirus, which is well known as severe fever with thrombocytopenia syndrome (SFTS) virus (SFTSV). The mortality rate of human HRTV infection is approximately 10%; however, neither approved anti-HRTV agents nor vaccines exist. An appropriate animal model should be developed to evaluate the efficacy of antiviral agents and vaccines against HRTV. The susceptibility of IFNAR^−/− mice with HRTV infection was evaluated using subcutaneous, intraperitoneal, and retro-orbital inoculation routes. IFNAR^−/− mice intraperitoneally infected with HRTV showed the most severe clinical signs, and the 50% lethal dose was 3.2 × 10⁶ TCID₅₀. Furthermore, to evaluate the utility of a novel lethal IFNAR^−/− mice model, IFNAR^−/− mice were orally administered favipiravir, ribavirin, or a solvent for 5 days immediately after a lethal dose of HRTV inoculation. The survival rates of the favipiravir-, ribavirin-, and solvent-administered mice were 100, 33, and 0%, respectively. The changes in bodyweights and HRTV RNA loads in the blood of favipiravir-treated IFNAR^−/− mice were the lowest among the three groups, which suggests that favipiravir is a promising drug candidate for the treatment of patients with HRTV infection.

Heartland bandavirus (HRTV) is a tick-borne virus identified in the United States in 2009. HRTV causes fever, fatigue, decreased appetite, headache, nausea, diarrhea, and muscle or joint pain in humans.

Owing to genotype-specific neutralizing antibodies, analyzing differences in the immunogenic variation among dengue virus (DENV) genotypes is central to effective vaccine development. Herein, we characterized the viral kinetics and antibody response induced by DENV type 2 Asian I (AI) and Asian/American (AA) genotypes using marmosets (Callithrix jacchus) as models. Two groups of marmosets were inoculated with AI and AA genotypes, and serial plasma samples were collected. Viremia levels were determined using quantitative reverse transcription-PCR, plaque assays, and antigen enzyme-linked immunosorbent assay (ELISA). Anti-DENV immunoglobulin M and G antibodies, neutralizing antibody titer, and antibody-dependent enhancement (ADE) activity were determined using ELISA, plaque reduction neutralization test, and ADE assay, respectively. The AI genotype induced viremia for a longer duration, but the AA genotype induced higher levels of viremia. After four months, the neutralizing antibody titer induced by the AA genotype remained high, but that induced by the AI genotype waned. ADE activity toward Cosmopolitan genotypes was detected in marmosets inoculated with the AI genotype. These findings indicate discrepancies between heterologous genotypes that influence neutralizing antibodies and viremia in marmosets, a critical issue in vaccine development.

Genotype V (GV) Japanese encephalitis virus (JEV) has emerged in Korea and China since 2009. Recent findings suggest that current Japanese encephalitis (JE) vaccines may reduce the ability to induce neutralizing antibodies against GV JEV compared to other genotypes. This study sought to produce a novel live attenuated JE vaccine with a high efficacy against GV JEV. Genotype I (GI)-GV intertypic recombinant strain rJEV-E^XZ0934-M41 (E^XZ0934), in which the E region of the GI Mie/41/2002 strain was replaced with that of GV strain XZ0934, was introduced with the same 10 attenuation substitutions in the E region found in the live attenuated JE vaccine strain SA 14-14-2 to produce a novel mutant virus rJEV-E^XZ/SA14142m-M41 (E^XZ/SA14142m). In addition, another mutant rJEV-E^M41/SA14142m-M41 (E^M41/SA14142m), which has the same substitutions in the Mie/41/2002, was also produced. The neuroinvasiveness and neurovirulence of the two mutant viruses were significantly reduced in mice. The mutant viruses induced neutralizing antibodies against GV JEV in mice. The growth of E^XZ/SA14142m was lower than that of E^M41/SA14142m. In mouse challenge tests, a single inoculation with a high dose of the mutants blocked lethal GV JEV infections; however, the protective efficacy of E^XZ/SA14142m was weaker than that of E^M41/SA14142m in low-dose inoculations. The lower protection potency of E^XZ/SA14142m may be ascribed to the reduced growth ability caused by the attenuation mutations.

Zika virus (ZIKV) infection during pregnancy causes a wide spectrum of congenital abnormalities and postnatal developmental sequelae such as fetal loss, intrauterine growth restriction (IUGR), microcephaly, or motor and neurodevelopmental disorders. Here, we investigated whether a mouse pregnancy model recapitulated a wide range of symptoms after congenital ZIKV infection, and whether the embryonic age of congenital infection changed the fetal or postnatal outcomes. Infection with ZIKV strain PRVABC59 from embryonic day 6.5 (E6.5) to E8.5, corresponding to the mid-first trimester in humans, caused fetal death, fetal resorption, or severe IUGR, whereas infection from E9.5 to E14.5, corresponding to the late-first to second trimester in humans, caused stillbirth, neonatal death, microcephaly, and postnatal growth deficiency. Furthermore, 4-week-old offspring born to dams infected at E12.5 showed abnormalities in neuropsychiatric state, motor behavior, autonomic function, or reflex and sensory function. Thus, our model recapitulated the multiple symptoms seen in human cases, and the embryonic age of congenital infection was one of the determinant factors of offspring outcomes in mice. Furthermore, maternal neutralizing antibodies protected the offspring from neonatal death after congenital infection at E9.5, suggesting that neonatal death in our model could serve as criteria for screening of vaccine candidates.