We provide research findings on the physics of aerosol and droplet dispersion relevant to the hypothesized aerosol transmission of SARS-CoV-2 during the current pandemic. We utilize physics-based modeling at different levels of complexity, along with previous literature on coronaviruses, to investigate the possibility of airborne transmission. The previous literature, our 0D-3D simulations by various physics-based models, and theoretical calculations, indicate that the typical size range of speech and cough originated droplets (d⩽20μm) allows lingering in the air for O(1h) so that they could be inhaled. Consistent with the previous literature, numerical evidence on the rapid drying process of even large droplets, up to sizes O(100μm), into droplet nuclei/aerosols is provided. Based on the literature and the public media sources, we provide evidence that the individuals, who have been tested positive on COVID-19, could have been exposed to aerosols/droplet nuclei by inhaling them in significant numbers e.g. O(100). By 3D scale-resolving computational fluid dynamics (CFD) simulations, we give various examples on the transport and dilution of aerosols (d⩽20μm) over distances O(10m) in generic environments. We study susceptible and infected individuals in generic public places by Monte-Carlo modelling. The developed model takes into account the locally varying aerosol concentration levels which the susceptible accumulate via inhalation. The introduced concept, ’exposure time’ to virus containing aerosols is proposed to complement the traditional ’safety distance’ thinking. We show that the exposure time to inhale O(100) aerosols could range from O(1s) to O(1min) or even to O(1h) depending on the situation. The Monte-Carlo simulations, along with the theory, provide clear quantitative insight to the exposure time in different public indoor environments.

In 2018, the family Arenaviridae was expanded by inclusion of 1 new genus and 5 novel species. At the same time, the recently established order Bunyavirales was expanded by 3 species. This article presents the updated taxonomy of the family Arenaviridae and the order Bunyavirales as now accepted by the International Committee on Taxonomy of Viruses (ICTV) and summarizes additional taxonomic proposals that may affect the order in the near future.

Boid inclusion body disease (BIBD) is a progressive, usually fatal disease of constrictor snakes, characterized by cytoplasmic inclusion bodies (IB) in a wide range of cell types. To identify the causative agent of the disease, we established cell cultures from BIBD-positive and -negative boa constrictors. The IB phenotype was maintained in cultured cells of affected animals, and supernatants from these cultures caused the phenotype in cultures originating from BIBD-negative snakes. Viruses were purified from the supernatants by ultracentrifugation and subsequently identified as arenaviruses. Purified virus also induced the IB phenotype in naive cells, which fulfilled Koch's postulates in vitro . One isolate, tentatively designated University of Helsinki virus (UHV), was studied in depth. Sequencing confirmed that UHV is a novel arenavirus species that is distinct from other known arenaviruses including those recently identified in snakes with BIBD. The morphology of UHV was established by cryoelectron tomography and subtomographic averaging, revealing the trimeric arenavirus spike structure at 3.2-nm resolution. Immunofluorescence, immunohistochemistry, and immunoblotting with a polyclonal rabbit antiserum against UHV and reverse transcription-PCR (RT-PCR) revealed the presence of genetically diverse arenaviruses in a large cohort of snakes with BIBD, confirming the causative role of arenaviruses. Some snakes were also found to carry arenavirus antibodies. Furthermore, mammalian cells (Vero E6) were productively infected with UHV, demonstrating the potential of arenaviruses to cross species barriers. In conclusion, we propose the newly identified lineage of arenaviruses associated with BIBD as a novel taxonomic entity, boid inclusion body disease-associated arenaviruses (BIBDAV), in the family Arenaviridae .

Puumala virus (PUUV) is a negative-stranded RNA virus in the genus Hantavirus , family Bunyaviridae. In this study, detailed phylogenetic analysis was performed on 42 complete S segment sequences of PUUV originated from several European countries, Russia, and Japan, the largest set available thus far for hantaviruses. The results show that PUUV sequences form seven distinct and well-supported genetic lineages; within these lineages, geographical clustering of genetic variants is observed. The overall phylogeny of PUUV is star-like, suggesting an early split of genetic lineages. The individual PUUV lineages appear to be independent, with the only exception to this being the Finnish and the Russian lineages that are closely connected to each other. Two strains of PUUV-like virus from Japan form the most ancestral lineage diverging from PUUV. Recombination points within the S segment were searched for and evidence for intralineage recombination events was seen in the Finnish, Russian, Danish, and Belgian lineages of PUUV. Molecular clock analysis showed that PUUV is a stable virus, evolving slowly at a rate of 0.7 × 10 ⁻⁷ to 2.2 × 10 ⁻⁶ nt substitutions per site per year.