A novel nairovirus associated with acute febrile illness in Hokkaido, Japan.

The increasing burden of tick-borne orthonairovirus infections, such as Crimean-Congo hemorrhagic fever, is becoming a global concern for public health. In the present study, we identify a novel orthonairovirus, designated Yezo virus (YEZV), from two patients showing acute febrile illness with thrombocytopenia and leukopenia after tick bite in Hokkaido, Japan, in 2019 and 2020, respectively. YEZV is phylogenetically grouped with Sulina virus detected in Ixodes ricinus ticks in Romania. YEZV infection has been confirmed in seven patients from 2014-2020, four of whom were co-infected with Borrelia spp. Antibodies to YEZV are found in wild deer and raccoons, and YEZV RNAs have been detected in ticks from Hokkaido. In this work, we demonstrate that YEZV is highly likely to be the causative pathogen of febrile illness, representing the first report of an endemic infection associated with an orthonairovirus potentially transmitted by ticks in Japan.

Ticks associated with macquarie island penguins carry arboviruses from four genera.

Macquarie Island, a small subantarctic island, is home to rockhopper, royal and king penguins, which are often infested with the globally distributed seabird tick, Ixodes uriae. A flavivirus, an orbivirus, a phlebovirus, and a nairovirus were isolated from these ticks and partial sequences obtained. The flavivirus was nearly identical to Gadgets Gully virus, isolated some 30 year previously, illustrating the remarkable genetic stability of this virus. The nearest relative to the orbivirus (for which we propose the name Sandy Bay virus) was the Scottish Broadhaven virus, and provided only the second available sequences from the Great Island orbivirus serogroup. The phlebovirus (for which we propose the name Catch-me-cave virus) and the previously isolated Precarious Point virus were distinct but related, with both showing homology with the Finnish Uukuniemi virus. These penguin viruses provided the second and third available sequences for the Uukuniemi group of phleboviruses. The nairovirus (for which we propose the name Finch Creek virus) was shown to be related to the North American Tillamook virus, the Asian Hazara virus and Nairobi sheep disease virus. Macquarie Island penguins thus harbour arboviruses from at least four of the seven arbovirus-containing genera, with related viruses often found in the northern hemisphere.

Ultrastructural studies on the replication and morphogenesis of Nairobi sheep disease virus, a Nairovirus.

The Nairovirus Nairobi sheep disease virus (NSDV) affects sheep and goats causing severe hemorrhagic gastroenteritis and high mortality. Replication and morphogenesis of NSDV was determined by electron microscopic examination of ultra-thin sections of 143B and BHK-21 cells at varying times after infection. By 4 h post-infection (p.i.) of 143B cells, virions budding from the luminal side of the bilayer membrane of smooth membrane vesicles were observed. Morphologically mature virus particles were electron-dense, spherical and of uniform size (100 nm diameter) and accumulated in smooth membrane vesicles associated with the Golgi complex. In BHK-21 clone 13 cells, mature virus particles in smooth membrane vesicles were present by 8 h p.i. The morphogenesis of NSDV was restricted to the smooth membrane vesicles of Golgi complex, and budding of virus from other sites was not detected. Extracellular virus particles were observed by 10 h p.i., before expression of cytopathic effects. The cytopathic effects were observed at 24 h p.i. in 143B cells and at 36 h p.i. in BHK-21 cells. The morphology and morphogenesis of NSDV in BHK-21 cells and in 143B cells resembles that of other members of the family Bunyaviridae.

Structure and morphogenesis of Dugbe virus (Bunyaviridae, Nairovirus) studied by immunogold electron microscopy of ultrathin cryosections.

We have studied the structure and morphogenesis of Dugbe (DUG) virus (Bunyaviridae, Nairovirus) in cultured porcine kidney (PS) cells and a tick cell line (Ra 243) using immunogold electron microscopy. DUG virus is a tickborne arbovirus, considered to be a low health hazard, that is antigenically and genetically related to Crimean Congo haemorrhagic fever (CCHF) virus (Marriott et al., 1990). We have investigated the maturation and intracellular transport of DUG virus particles as a model for other more pathogenic nairoviruses using monoclonal antibodies for immunogold labelling of ultrathin cryosections and immunofluorescence techniques. The spherical DUG virus particle measures about 90 nm in diameter, with a 5 nm thick membrane covered by 5-7 nm long projections or "spikes". These projections form hollow cylindrical morphological units, about 5 nm in diameter. DUG virus infection caused only a slight cytopathogenic effect in mammalian cells and none in tick cells. DUG virus particles assembled by budding from the Golgi complex, where the DUG virus glycoprotein G1 accumulated in vesicles originating from Golgi cisternae. The nucleocapsid protein N accumulated in scattered foci throughout the cytoplasm, and this appears to be related to the limited maturation of DUG virus particles that occurred. The reduced number of budding virus particles observed in tick cells was correlated with the reduced cytopathology observed.