Evolutionary history of Simbu serogroup orthobunyaviruses in the Australian episystem

Replication of Akabane virus and related orthobunyaviruses in a fetal-bovine-brain-derived cell line

Akabane virus (AKAV), Aino virus, Peaton virus, Sathuperi virus, and Shamonda virus are arthropod-borne viruses belonging to the order Elliovirales, family Peribunyaviridae, genus Orthobunyavirus. These viruses cause or may cause congenital malformations in ruminants, including hydranencephaly, poliomyelitis, and arthrogryposis, although their pathogenicity may vary among field cases. AKAV may cause relatively severe congenital lesions such as hydranencephaly in calves. Furthermore, strains of AKAV genogroups I and II exhibit different disease courses. Genogroup I strains predominantly cause postnatal viral encephalomyelitis, while genogroup II strains are primarily detected in cases of congenital malformation. However, the biological properties of AKAV and other orthobunyaviruses are insufficiently investigated in hosts in the field and in vitro. Here, we used an immortalized bovine brain cell line (FBBC-1) to investigate viral replication efficiency, cytopathogenicity, and host innate immune responses. AKAV genogroup II and Shamonda virus replicated to higher titers in FBBC-1 cells compared with the other viruses, and only AKAV caused cytopathic effects. These results may be associated with the severe congenital lesions in the brain caused by AKAV genogroup II. AKAV genogroup II strains replicated to higher titers in FBBC-1 cells than AKAV genogroup I strains, suggesting that genogroup II strains replicated more efficiently in fetal brain cells, accounting for the detection of the latter strains mainly in fetal infection cases. Therefore, FBBC-1 cells may serve as a valuable tool for investigating the virulence and tropism of the orthobunyaviruses for bovine neonatal brain tissues in vitro.

Identification of a broadly neutralizing epitope within Gc protein of Akabane virus using newly prepared neutralizing monoclonal antibodies

Akabane virus (AKAV) is characterized by abortion, stillbirth, premature birth, and congenital deformities in livestock and is widely distributed throughout Australia, Southeast Asia, East Asia, the Middle East, and Africa. Gc protein is the major neutralizing target of AKAV and is often considered as an immunogen to prepare neutralizing antibodies. In this study, we prepared and characterized three monoclonal antibodies (mAbs), 4D1, 4E6, and 4F12, against the Gc protein of AKAV (TJ2016 strain). Western blot (WB) and indirect immunofluorescence assay (IFA) analysis proved that the mAbs can react with both the truncated recombinant AKAV Gc protein and the natural Gc protein produced in the AKAV-infected cells. Further research demonstrated that these mAbs possess neutralizing activity. We next defined a neutralizing epitope 1134SVQSFDGKL1142 by screening a panel of overlapping peptides spanning the truncated Gc protein (aa991∼1232) using the generated neutralizing mAbs. Bioinformatic analysis shows that the neutralizing epitope is highly conserved across different genotypes of AKAV. The newly produced neutralizing mAbs and the identified neutralizing epitope in this study enrich the antigenic epitope information of the AKAV Gc protein and could have potential applications in the development of antigen and antibody detection systems that are specific to AKAV.

Differential role of NSs genes in the neurovirulence of two genogroups of Akabane virus causing postnatal encephalomyelitis

Akabane virus (AKAV) is a member of the genus Orthobunyavirus, family Peribunyaviridae. In addition to AKAV strains that cause fetal Akabane disease, which is characterized by abortion in ruminants, some AKAV strains cause postnatal infection characterized by nonsuppurative encephalomyelitis in ruminants. Here, we focused on the NSs protein, a virulence factor for most viruses belonging to the genus Orthobunyavirus, and we hypothesized that this protein would act as a neurovirulence factor in AKAV strains causing postnatal encephalomyelitis. We generated AKAV strains that were unable to produce the NSs protein, derived from two different genogroups, genogroups I and II, and then examined the role of their NSs proteins by inoculating mice intracerebrally with these modified viruses. Our results revealed that the neurovirulence of genogroup II strains is dependent on the NSs protein, whereas that of genogroup I strains is independent of this protein. Notably, infection of primary cultured bovine cells with these viruses suggested that the NSs proteins of both genogroups suppress innate immune-related gene expression with equal efficiency. These results indicate differences in the determinants of virulence of orthobunyaviruses.

Circulation of Ngari Virus in Livestock, Kenya

Ngari virus (NRIV) is a mosquito-borne reassortant orthobunyavirus that causes severe febrile illness and hemorrhagic fever in humans and small ruminants. Due to limited diagnostics and surveillance, NRIV has only been detected sporadically during Rift Valley fever virus outbreaks. Little is known on its interepidemic maintenance and geographic distribution. In this study, sera from cattle, goats, and sheep were collected through a cross-sectional survey after the rainy seasons between 2020 and 2021 in two pastoralist-dominated semiarid ecosystems, Baringo and Kajiado counties in Kenya. NRIV was detected in 11 apparently healthy animals (11/2,039, 0.54%) by RT-PCR and isolated in cell culture from seven individuals. Growth analyses displayed efficient replication in cells from sheep and humans in contrast to weak replication in goat cells. NRIV infection of a wide variety of different vector cells showed only rapid replication in Aedes albopictus cells but not in cells derived from other mosquito species or sandflies. Phylogenetic analyses of complete-coding sequences of L, M, and S segments of four viruses showed that the Kenyan sequences established a monophyletic clade most closely related to a NRIV sequence from a small ruminant from Mauritania. NRIV neutralizing reactivity in cattle, goats, and sheep were 41.6% (95% CI = 30 to 54.3), 52.4% (95% CI = 37.7 to 66.6), and 19% (95% CI = 9.7 to 33.6), respectively. This is the first detection of NRIV in livestock in Kenya. Our results demonstrate active and undetected circulation of NRIV in the three most common livestock species highlighting the need for an active one-health surveillance of host networks, including humans, livestock, and vectors. IMPORTANCE Surveillance of vectors and hosts for infection with zoonotic arthropod-borne viruses is important for early detection and intervention measures to prevent outbreaks. Here, we report the undetected circulation of Ngari virus (NRIV) in apparently healthy cattle, sheep, and goats in Kenya. NRIV is associated with outbreaks of hemorrhagic fever in humans and small ruminants. We demonstrate the isolation of infectious virus from several animals as well as presence of neutralizing antibodies in 38% of the tested animals. Our data indicate active virus circulation and endemicity likely having important implications for human and animal health.

Molecular epidemiology of Akabane virus in Taiwan

Background

Akabane virus (AKAV) is a teratogenic and neuropathogenic arbovirus that infects livestock and wild animals. AKAVs are endemic arboviruses from dairy farms in Taiwan in 1989, and the first sequence was detected in cattle with nonsuppurative encephalitis in 1992.

Objectives

This study aims to understand the epidemiological relationships of the akabane viruses between Taiwan and nearby places.

Methods

In this study, 17 specimens were identified or isolated from vector insects, and ruminant fetuses collected from 1992 to 2015 were sequenced and analysed.

Results

Sequence analyses revealed all Taiwanese AKAVs belonged to genogroup Ia but diverged into two clusters in the phylogenetic trees, implying that at least two invasive events of AKAV may have occurred in Taiwan.

Conclusions

The two clusters of AKAVs could still be identified in Taiwan in 2015, and a reassortment event was observed, indicating that the two clusters of AKAVs are already endemic in Taiwan.

Factors associated with seropositivity to Aino virus among sheep and goats in South Korea

Aino virus infection is responsible for epizootic and/or sporadic outbreaks of abortions, stillbirths and premature delivery among pregnant ruminants. The epizootiology of Aino virus infection is poorly defined in South Korea, therefore our aim was to assess its seroprevalence among sheep and goats. We also wanted to evaluate management and regional risk factors that might influence the frequency of infection. Between 2012 and 2013, 26 of 331 flocks (7.9%) and 139 of 915 heads (15.2%) were found serologically positive. In 2018, when samples were again collected in the same regions, 35 of 308 flocks (11.4%) and 89 of 735 heads (12.1%) showed serum-neutralising antibodies against Aino virus. Our results revealed that the age class and history of reproductive problems in the flocks are connected to an increased risk of being positive. The management risk factor attributes showed that preventive measures, such as the routine application of insecticide in farms, decreased the odds for seropositivity to Aino virus (OR = 0.453, P = 0.001). We observed a significant difference in the individual likelihood of being positive in the southern and western provinces with respect to that in the northern and eastern provinces, respectively (OR = 2.199, P < 0.001 and OR = 2.177, P < 0.001). The results of this study may serve as a basis for future epizootic studies on Aino virus infection in South Korea.

Different organ and tissue tropism between Akabane virus genogroups in a mouse model

Akabane virus (AKAV) is an etiological agent that is teratogenic to the fetus of domestic ruminants, causing a significant loss of reproduction in livestock. In East Asia, AKAV isolates form two major clusters: genogroups I and II. In recent years, genogroup I isolates have also been associated with postnatal encephalomyelitis, mainly in calves. Here, we compared the pathogenicity in mice using genogroup I Iriki and genogroup II OBE-1 strains. Only mice infected intraperitoneally with the Iriki strain died and showed marked replication in the central nervous system (CNS) and lymphoid tissues. A more elevated blood-brain barrier (BBB) permeability was found in the Iriki-infected mice in the clinical phase, indicating that the BBB might be a possible route of viral transmission from the periphery to the CNS. These findings demonstrate that the Iriki strain presents greater neurovirulence and neuroinvasiveness compared with the OBE-1 strain, determining different AKAV pathogenicity among genogroups.

Baseline mapping of Oropouche virology, epidemiology, therapeutics, and vaccine research and development

Oropouche virus (OROV) is an arthropod-borne orthobunyavirus found in South America and causes Oropouche fever, a febrile infection similar to dengue. It is the second most prevalent arthropod-borne viral disease in South America after dengue. Over 500,000 cases have been diagnosed since the virus was first discovered in 1955; however, this is likely a significant underestimate given the limited availability of diagnostics. No fatalities have been reported to date, however, up to 60% of cases have a recurrent phase of disease within one month of recovery from the primary disease course. The main arthropod vector is the biting midge Culicoides paraensis, which has a geographic range as far north as the United States and demonstrates the potential for OROV to geographically expand. The transmission cycle is incompletely understood and vertebrate hosts include both non-human primates and birds further supporting the potential ability of the virus to spread. A number of candidate antivirals have been evaluated against OROV in vitro but none showed antiviral activity. Surprisingly, there is only one report in the literature on candidate vaccines. We suggest that OROV is an undervalued pathogen much like chikungunya, Schmallenberg, and Zika viruses were before they emerged. Overall, OROV is an important emerging disease that has been under-investigated and has the potential to cause large epidemics in the future. Further research, in particular candidate vaccines, is needed for this important pathogen.

Seroepidemiology of Aino Virus in Farmed and Free-Ranging Cervids in the Republic of Korea

Aino virus is an infectious, non-contagious, vector-borne agent that has been implicated in arthrogryposis-hydranencephaly syndrome in newborn cattle, sheep, and goats. Information about reservoirs and host animal species susceptible to Aino virus remains unclear. To further explore the role of cervids in Aino virus infection transmission, we investigated cervid sera to determine the prevalence of Aino virus-neutralizing antibodies and to identify factors correlated with antibody positivity. We screened cervid serum samples collected in the Republic of Korea to better understand infection patterns in this animal species. Overall, Aino virus infection was widespread; 75 of 716 (10.5%, 95% [95% CI] = 8.4-13.4) farmed-cervid serum samples collected from 292 herds contained antibodies to Aino virus. Serological evidence of Aino virus infection was demonstrated in 5 of 43 free-ranging cervids, accounting for a prevalence rate of ~11.6% (95% CI = 4.6-26.4). Our results revealed that age class and geographic location affected seroprevalence. The main risk factors associated with Aino virus seroprevalence were older age (> 2 years old, OR = 2.221, 95% CI = 1.209-4.079, P = 0.009 in adults), southern provinces (OR = 2.432, 95% CI = 1.445-4.093, P = 0.001), and western provinces (OR = 1.905, 95% CI = 1.041-3.488, P = 0.034). The results in this study suggest that cervid species might serve as important hosts for the transmission of Aino virus, highlighting the need for careful monitoring of Aino virus infections in cervids.

Differentiation of Antibodies against Selected Simbu Serogroup Viruses by a Glycoprotein Gc-Based Triplex ELISA

The Simbu serogroup of orthobunyaviruses includes several pathogens of veterinary importance, among them Schmallenberg virus (SBV), Akabane virus (AKAV) and Shuni virus (SHUV). They infect predominantly ruminants and induce severe congenital malformation. In adult animals, the intra vitam diagnostics by direct virus detection is limited to only a few days due to a short-lived viremia. For surveillance purposes the testing for specific antibodies is a superior approach. However, the serological differentiation is hampered by a considerable extent of cross-reactivity, as viruses were assigned into this serogroup based on antigenic relatedness. Here, we established a glycoprotein Gc-based triplex enzyme-linked immunosorbent assay (ELISA) for the detection and differentiation of antibodies against SBV, AKAV, and SHUV. A total of 477 negative samples of various ruminant species, 238 samples positive for SBV-antibodies, 36 positive for AKAV-antibodies and 53 SHUV antibody-positive samples were tested in comparison to neutralization tests. For the newly developed ELISA, overall diagnostic specificities of 84.56%, 94.68% and 89.39% and sensitivities of 89.08%, 69.44% and 84.91% were calculated for SBV, AKAV and SHUV, respectively, with only slight effects of serological cross-reactivity on the diagnostic specificity. Thus, this test system could be used for serological screening in suspected populations or as additional tool during outbreak investigations.

Family Level Phylogenies Reveal Relationships of Plant Viruses within the Order Bunyavirales

Bunyavirales are negative-sense segmented RNA viruses infecting arthropods, protozoans, plants, and animals. This study examines the phylogenetic relationships of plant viruses within this order, many of which are recently classified species. Comprehensive phylogenetic analyses of the viral RNA dependent RNA polymerase (RdRp), precursor glycoprotein (preGP), the nucleocapsid (N) proteins point toward common progenitor viruses. The RdRp of Fimoviridae and Tospoviridae show a close evolutional relationship while the preGP of Fimoviridae and Phenuiviridae show a closed relationship. The N proteins of Fimoviridae were closer to the Phasmaviridae, the Tospoviridae were close to some Phenuiviridae members and the Peribunyaviridae. The plant viral movement proteins of species within the Tospoviridae and Phenuiviridae were more closely related to each other than to members of the Fimoviridae. Interestingly, distal ends of 3′ and 5′ untranslated regions of species within the Fimoviridae shared similarity to arthropod and vertebrate infecting members of the Cruliviridae and Peribunyaviridae compared to other plant virus families. Co-phylogeny analysis of the plant infecting viruses indicates that duplication and host switching were more common than co-divergence with a host species.

Endemic and Emerging Arboviruses in Domestic Ruminants in East Asia

Epizootic congenital abnormalities caused by Akabane, Aino, and Chuzan viruses have damaged the reproduction of domestic ruminants in East Asia for many years. In the past, large outbreaks of febrile illness related to bovine ephemeral fever and Ibaraki viruses severely affected the cattle industry in that region. In recent years, vaccines against these viruses have reduced the occurrence of diseases, although the viruses are still circulating and have occasionally caused sporadic and small-scaled epidemics. Over a long-term monitoring period, many arboviruses other than the above-mentioned viruses have been isolated from cattle and Culicoides biting midges in Japan. Several novel arboviruses that may infect ruminants (e.g., mosquito- and tick-borne arboviruses) were recently reported in mainland China based on extensive surveillance. It is noteworthy that some are suspected of being associated with cattle diseases. Malformed calves exposed to an intrauterine infection with orthobunyaviruses (e.g., Peaton and Shamonda viruses) have been observed. Epizootic hemorrhagic disease virus serotype 6 caused a sudden outbreak of hemorrhagic disease in cattle in Japan. Unfortunately, the pathogenicity of many other viruses in ruminants has been uncertain, although these viruses potentially affect livestock production. As global transportation grows, the risk of an accidental incursion of arboviruses is likely to increase in previously non-endemic areas. Global warming will also certainly affect the distribution and active period of vectors, and thus the range of virus spreads will expand to higher-latitude regions. To prevent anticipated damages to the livestock industry, the monitoring system for arboviral circulation and incursion should be strengthened; moreover, the sharing of information and preventive strategies will be essential in East Asia.