A Numerical Investigation into the Spread Characteristics of a Human Virus-Carrying Droplet in a Classroom Environment.

In public health, the transmission characteristics and laws of highly infectious virus-carrying particles in the air environment have become a hot topic. The study on the spread characteristics of human virus-carrying droplets in a typical densely populated space is necessary. As such, a classroom space lattice Boltzmann method (LBM) model with a dense population is established to simulate and analyze the spreading and diffusing behavior of pathogenic droplets. The results show that the dispersion density is mainly affected by the mainstream wind direction in the area of concern, and particle aggregation is more likely to form in the area close to the wind disturbance. Due to the dense thermal plumes, the droplet movement is a clear convergence towards the upper space of the classroom. This could explain the fact that people living above confirmed cases are now more likely to be infected.

Assessing suspension and infectivity times of virus-loaded aerosols involved in airborne transmission.

Airborne transmission occurs through droplet-mediated transport of viruses following the expulsion of an aerosol by an infected host. Transmission efficiency results from the interplay between virus survival in the drying droplet and droplet suspension time in the air, controlled by the coupling between water evaporation and droplet sedimentation. Furthermore, droplets are made of a respiratory fluid and thus, display a complex composition consisting of water and nonvolatile solutes. Here, we quantify the impact of this complex composition on the different phenomena underlying transmission. Solutes lead to a nonideal thermodynamic behavior, which sets an equilibrium droplet size that is independent of relative humidity. In contrast, solutes do not significantly hinder transport due to their low initial concentration. Realistic suspension times are computed and increase with increasing relative humidity or decreasing temperature. By uncoupling drying and suspended stages, we observe that enveloped viruses may remain infectious for hours in dried droplets. However, their infectivity decreases with increasing relative humidity or temperature after dozens of minutes. Examining expelled droplet size distributions in the light of these results leads to distinguishing two aerosols. Most droplets measure between 0 and 40 µm and compose an aerosol that remains suspended for hours. Its transmission efficiency is controlled by infectivity, which decreases with increasing humidity and temperature. Larger droplets form an aerosol that only remains suspended for minutes but corresponds to a much larger volume and thus, viral load. Its transmission efficiency is controlled by droplet suspension time, which decreases with increasing humidity and decreasing temperature.

Mosquito saliva enhances virus infection through sialokinin-dependent vascular leakage.

Viruses transmitted by Aedes mosquitoes are an increasingly important global cause of disease. Defining common determinants of host susceptibility to this large group of heterogenous pathogens is key for informing the rational design of panviral medicines. Infection of the vertebrate host with these viruses is enhanced by mosquito saliva, a complex mixture of salivary-gland-derived factors and microbiota. We show that the enhancement of infection by saliva was dependent on vascular function and was independent of most antisaliva immune responses, including salivary microbiota. Instead, the Aedes gene product sialokinin mediated the enhancement of virus infection through a rapid reduction in endothelial barrier integrity. Sialokinin is unique within the insect world as having a vertebrate-like tachykinin sequence and is absent from Anopheles mosquitoes, which are incompetent for most arthropod-borne viruses, whose saliva was not proviral and did not induce similar vascular permeability. Therapeutic strategies targeting sialokinin have the potential to limit disease severity following infection with Aedes-mosquito-borne viruses.

Enteric viruses replicate in salivary glands and infect through saliva.

Enteric viruses like norovirus, rotavirus and astrovirus have long been accepted as spreading in the population through fecal-oral transmission: viruses are shed into feces from one host and enter the oral cavity of another, bypassing salivary glands (SGs) and reaching the intestines to replicate, be shed in feces and repeat the transmission cycle1. Yet there are viruses (for example, rabies) that infect the SGs2,3, making the oral cavity one site of replication and saliva one conduit of transmission. Here we report that enteric viruses productively and persistently infect SGs, reaching titres comparable to those in the intestines. We demonstrate that enteric viruses get released into the saliva, identifying a second route of viral transmission. This is particularly significant for infected infants, whose saliva directly transmits enteric viruses to their mothers' mammary glands through backflow during suckling. This sidesteps the conventional gut-mammary axis route4 and leads to a rapid surge in maternal milk secretory IgA antibodies5,6. Lastly, we show that SG-derived spheroids7 and cell lines8 can replicate and propagate enteric viruses, generating a scalable and manageable system of production. Collectively, our research uncovers a new transmission route for enteric viruses with implications for therapeutics, diagnostics and importantly sanitation measures to prevent spread through saliva.

COVID-19-lessons for zoonotic disease.

Disease emergence is driven by human-animal contact in a global viral ecosystem.

Honey bees and climate explain viral prevalence in wild bee communities on a continental scale.

Viruses are omnipresent, yet the knowledge on drivers of viral prevalence in wild host populations is often limited. Biotic factors, such as sympatric managed host species, as well as abiotic factors, such as climatic variables, are likely to impact viral prevalence. Managed and wild bees, which harbor several multi-host viruses with a mostly fecal-oral between-species transmission route, provide an excellent system with which to test for the impact of biotic and abiotic factors on viral prevalence in wild host populations. Here we show on a continental scale that the prevalence of three broad host viruses: the AKI-complex (Acute bee paralysis virus, Kashmir bee virus and Israeli acute paralysis virus), Deformed wing virus, and Slow bee paralysis virus in wild bee populations (bumble bees and solitary bees) is positively related to viral prevalence of sympatric honey bees as well as being impacted by climatic variables. The former highlights the need for good beekeeping practices, including Varroa destructor management to reduce honey bee viral infection and hive placement. Furthermore, we found that viral prevalence in wild bees is at its lowest at the extreme ends of both temperature and precipitation ranges. Under predicted climate change, the frequency of extremes in precipitation and temperature will continue to increase and may hence impact viral prevalence in wild bee communities.

Novel viruses highlight risks of Asia's wild animal trade.

Sampling of game in China reveals many viral threats.

Exploring the Role of Innate Lymphocytes in the Immune System of Bats and Virus-Host Interactions.

Bats are reservoirs of a large number of viruses of global public health significance, including the ancestral virus for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and the causative agent of coronavirus disease 2019 (COVID-19). Although bats are natural carriers of multiple pathogenic viruses, they rarely display signs of disease. Recent insights suggest that bats have a more balanced host defense and tolerance system to viral infections that may be linked to the evolutionary adaptation to powered flight. Therefore, a deeper understanding of bat immune system may provide intervention strategies to prevent zoonotic disease transmission and to identify new therapeutic targets. Similar to other eutherian mammals, bats have both innate and adaptive immune systems that have evolved to detect and respond to invading pathogens. Bridging these two systems are innate lymphocytes, which are highly abundant within circulation and barrier tissues. These cells share the characteristics of both innate and adaptive immune cells and are poised to mount rapid effector responses. They are ideally suited as the first line of defense against early stages of viral infections. Here, we will focus on the current knowledge of innate lymphocytes in bats, their function, and their potential role in host-pathogen interactions. Moreover, given that studies into bat immune systems are often hindered by a lack of bat-specific research tools, we will discuss strategies that may aid future research in bat immunity, including the potential use of organoid models to delineate the interplay between innate lymphocytes, bat viruses, and host tolerance.

Natural rodent model of viral transmission reveals biological features of virus population dynamics.

Emerging viruses threaten global health, but few experimental models can characterize the virus and host factors necessary for within- and cross-species transmission. Here, we leverage a model whereby pet store mice or rats-which harbor natural rodent pathogens-are cohoused with laboratory mice. This "dirty" mouse model offers a platform for studying acute transmission of viruses between and within hosts via natural mechanisms. We identified numerous viruses and other microbial species that transmit to cohoused mice, including prospective new members of the Coronaviridae, Astroviridae, Picornaviridae, and Narnaviridae families, and uncovered pathogen interactions that promote or prevent virus transmission. We also evaluated transmission dynamics of murine astroviruses during transmission and spread within a new host. Finally, by cohousing our laboratory mice with the bedding of pet store rats, we identified cross-species transmission of a rat astrovirus. Overall, this model system allows for the analysis of transmission of natural rodent viruses and is a platform to further characterize barriers to zoonosis.

Healthcare worker protection against epidemic viral respiratory disease.

Lower respiratory infections are often caused or precipitated by viruses and are a leading cause of global morbidity and mortality. Mutations in these viral genomes can produce highly infectious strains that transmit across species and have the potential to initiate epidemic, or pandemic, human viral respiratory disease. Transmission between humans primarily occurs via the airborne route and is accelerated by our increasingly interconnected and globalised society. To this date, there have been four major human viral respiratory outbreaks in the 21st century. Healthcare workers (HCWs) are at particular risk during respiratory epidemics or pandemics. This is due to crowded working environments where social distancing, or wearing respiratory personal protective equipment for prolonged periods, might prove difficult, or performing medical procedures that increase exposure to virus-laden aerosols, or bodily fluids. This review aims to summarise the evidence and approaches to occupational risk and protection of HCWs during epidemic or pandemic respiratory viral disease.

ZOVER: the database of zoonotic and vector-borne viruses.

Emerging infectious diseases significantly threaten global public health and socioeconomic security. The majority of emerging infectious disease outbreaks are caused by zoonotic/vector-borne viruses. Bats and rodents are the two most important reservoir hosts of many zoonotic viruses that can cross species barriers to infect humans, whereas mosquitos and ticks are well-established major vectors of many arboviral diseases. Moreover, some emerging zoonotic diseases require a vector to spread or are intrinsically vector-borne and zoonotically transmitted. In this study, we present a newly upgraded database of zoonotic and vector-borne viruses designated ZOVER (http://www.mgc.ac.cn/ZOVER). It incorporates two previously released databases, DBatVir and DRodVir, for bat- and rodent-associated viruses, respectively, and further collects up-to-date knowledge on mosquito- and tick-associated viruses to establish a comprehensive online resource for zoonotic and vector-borne viruses. Additionally, it integrates a set of online visualization tools for convenient comparative analyses to facilitate the discovery of potential patterns of virome diversity and ecological characteristics between/within different viral hosts/vectors. The ZOVER database will be a valuable resource for virologists, zoologists and epidemiologists to better understand the diversity and dynamics of zoonotic and vector-borne viruses and conduct effective surveillance to monitor potential interspecies spillover for efficient prevention and control of future emerging zoonotic diseases.

VThunter: a database for single-cell screening of virus target cells in the animal kingdom.

Viral infectious diseases are a devastating and continuing threat to human and animal health. Receptor binding is the key step for viral entry into host cells. Therefore, recognizing viral receptors is fundamental for understanding the potential tissue tropism or host range of these pathogens. The rapid advancement of single-cell RNA sequencing (scRNA-seq) technology has paved the way for studying the expression of viral receptors in different tissues of animal species at single-cell resolution, resulting in huge scRNA-seq datasets. However, effectively integrating or sharing these datasets among the research community is challenging, especially for laboratory scientists. In this study, we manually curated up-to-date datasets generated in animal scRNA-seq studies, analyzed them using a unified processing pipeline, and comprehensively annotated 107 viral receptors in 142 viruses and obtained accurate expression signatures in 2 100 962 cells from 47 animal species. Thus, the VThunter database provides a user-friendly interface for the research community to explore the expression signatures of viral receptors. VThunter offers an informative and convenient resource for scientists to better understand the interactions between viral receptors and animal viruses and to assess viral pathogenesis and transmission in species. Database URL: https://db.cngb.org/VThunter/.

Spatial Modeling and Analysis of Human Traffic and Infectious Virus Spread in Community Networks.

The use of network models to study the spread of infectious diseases is gaining increasing interests. They allow the flexibility to represent epidemic systems as networks of components with complex and interconnected structures. However, most of previous studies are based on networks of individuals as nodes and their social relationships (e.g., friendship, workplace connections) as links during the virus spread process. Notably, the transmission and spread of infectious viruses are more pertinent to human dynamics (e.g., their movements and interactions with others) in the spatial environment. This paper presents a novel network-based simulation model of human traffic and virus spread in community networks. We represent spatial points of interests (POI) as nodes where human subjects interact and perform activities, while edges connect these POIs to form a community network. Specifically, we derive the spatial network from the geographical information systems (GIS) data to provide a detailed representation of the underlying community network, on which human subjects perform activities and form traffics that impact the process of virus transmission and spread. The proposed framework is evaluated and validated in a community of university campus. Experimental results showed that the proposed simulation model is capable of describing interactive human activities at an individual level, as well as capturing the spread dynamics of infectious diseases. This framework can be extended to a wide variety of infectious diseases and shows strong potentials to aid the design of intervention policies for epidemic control.

Impacts of Cucurbit Chlorotic Yellows Virus (CCYV) on Biological Characteristics of Its Vector Bemisia tabaci (Hemiptera: Aleyrodidae) MED Species.

Plant viruses can change the phenotypes and defense pathways of the host plants and the performance of their vectors to facilitate their transmission. Cucurbit chlorotic yellows virus (CCYV) (Crinivirus), a newly reported virus occurring on cucurbit plants and many other plant species, is transmitted specifically by Bemisia tabaci MEAM1 (B biotype) and MED (Q biotype) cryptic species in a semipersistent manner. This study evaluated the impacts of CCYV on B. tabaci to better understand the plant-virus-vector interactions. By using CCYV-B. tabaci MED-cucumber as the model, we investigated whether or how a semipersistent plant virus impacts the biology of its whitefly vector. CCYV mRNAs were detectable in nymphs from first to fourth instars and adults of B. tabaci with different titers. Nymph instar durations and adult longevity of female whiteflies greatly extended on CCYV-infected plants, but nymph instar durations and adult longevity of male whiteflies were not significantly influenced. In addition, the body length and oviposition increased in adults feeding on CCYV-infected plants, but the hatching rates of eggs and survival rates of different stages were not affected. Most interestingly, the sex ratio (male:female) significantly reduced to 0.5:1 in whitefly populations on CCYV-infected plants, while the ratio remained about 1:1 on healthy plants. These results indicated that CCYV can significantly impact the biological characteristics of its vector B. tabaci. It is speculated that CCYV and B. tabaci have established a typical mutualist relationship mediated by host plants.

Transfer Rate of Enveloped and Nonenveloped Viruses between Fingerpads and Surfaces.

Fomites can represent a reservoir for pathogens, which may be subsequently transferred from surfaces to skin. In this study, we aim to understand how different factors (including virus type, surface type, time since last hand wash, and direction of transfer) affect virus transfer rates, defined as the fraction of virus transferred, between fingerpads and fomites. To determine this, 360 transfer events were performed with 20 volunteers using Phi6 (a surrogate for enveloped viruses), MS2 (a surrogate for nonenveloped viruses), and three clean surfaces (stainless steel, painted wood, and plastic). Considering all transfer events (all surfaces and both transfer directions combined), the mean transfer rates of Phi6 and MS2 were 0.17 and 0.26, respectively. Transfer of MS2 was significantly higher than that of Phi6 (P < 0.05). Surface type was a significant factor that affected the transfer rate of Phi6: Phi6 is more easily transferred to and from stainless steel and plastic than to and from painted wood. Direction of transfer was a significant factor affecting MS2 transfer rates: MS2 is more easily transferred from surfaces to fingerpads than from fingerpads to surfaces. Data from these virus transfer events, and subsequent transfer rate distributions, provide information that can be used to refine quantitative microbial risk assessments. This study provides a large-scale data set of transfer events with a surrogate for enveloped viruses, which extends the reach of the study to the role of fomites in the transmission of human enveloped viruses like influenza and SARS-CoV-2. IMPORTANCE This study created a large-scale data set for the transfer of enveloped viruses between skin and surfaces. The data set produced by this study provides information on modeling the distribution of enveloped and nonenveloped virus transfer rates, which can aid in the implementation of risk assessment models in the future. Additionally, enveloped and nonenveloped viruses were applied to experimental surfaces in an equivalent matrix to avoid matrix effects, so results between different viral species can be directly compared without confounding effects of different matrices. Our results indicating how virus type, surface type, time since last hand wash, and direction of transfer affect virus transfer rates can be used in decision-making processes to lower the risk of viral infection from transmission through fomites.