Is the increased transmissibility of SARS-CoV-2 variants driven by within or outside-host processes?

Understanding the factors that increase the transmissibility of the recently emerging variants of SARS-CoV-2 can aid in mitigating the COVID-19 pandemic. The enhanced transmissibility could be attributed to enhanced within-host processes, such as contagiousness (viral shedding by an infected individual) and infectivity (the probability of a susceptible individual to get infected), or outside-host processes, such as viral stability on surfaces and in the air. We utilized a mathematical model in order to theoretically analyze the specific mechanisms of virus transfer between an infected and susceptible individual. This allowed us to examine how the within-host or outside-host processes affect the overall viral transmission. Our analysis is based the available data on the Alpha, Epsilon and Delta variants as well as the currently emerging Omicron variant. We found that the higher transmissibility of the SARS-CoV-2 variants can be attributed only to within-host processes. Specifically, enhanced contagiousness drives the Delta variant transmissibility, while the Alpha, Epsilon and Omicron are characterized by an enhanced infectivity. Since outside-host processes have little contribution to the observed increase in the transmissibility, leading stricter hygienic and behavioral measures than those that were already applied are not expected to achieve a pronounced mitigating effect.

Effects of Selected Inherited Factors on Susceptibility to SARS-CoV-2 Infection and COVID-19 Progression

Genetic predispositions may influence geographical and interethnic differences in COVID-19 prevalence and mortality in affected populations. Of the many genes implicated in COVID-19 progression, a substantial number have no direct functional link on virus transfer/viability or on the host immune system. To address this knowledge deficit, a large number of in silico studies have recently been published. However, the results of these studies often contradict the findings of studies involving real patients. For example, the ACE2 has been shown to play an important role in regulating coronavirus entry into cells, but none of its variations have been directly associated with COVID-19 susceptibility or severity. Consistently was reported that increased risk of COVID-19 is associated with blood group A and with the APOE4 allele. Among other genes with potential impacts are the genes for CCR5, IL-10, CD14, TMPRSS2 and angiotensin-converting enzyme. Variants within the protein-coding genes OAS1 and LZTFL1 (transferred to the human genome from Neanderthals) are understood to be among the strongest predictors of disease severity. The intensive research efforts have helped to identify the genes and polymorphisms that contribute to SARS-CoV-2 infection and COVID-19 severity.

784. Efficiency of Quaternary Ammonium Disinfectants against SARS-CoV-2 and Coronavirus 229E

Background The recent pandemic of CoVid19 has increased our need to assess the impact of disinfectants on the inactivation of human coronaviruses. The goals of this study were 1) quantify the disinfection of SARS-CoV-2 and human coronavirus 229 inactivations by various quaternary ammonium formulations, and 2) demonstrate the impact of disinfectants on preventing fomite-to-finger transfer of coronaviruses. Methods We compared the inactivation of both SARS-Covid -2 and coronavirus 229E suspended in 5% fetal calf sera and dried on both metal and plastic surfaces. In addition, studies were conducted with a silinated quaternary ammonium compound that left a residual on the surface. Studies were also conducted on the finger transfer of coronavirus from various surfaces. The virus was allowed to dry on the surface for 30 minutes, then a transfer was conducted by placing the finger pad directly onto the contaminated surface. The finger was tested for the virus. The study was then repeated with virus-contaminated porcelain surfaces that were sprayed with a quaternary product or placed on a surface with a quaternary ammonium compound that left a residual. Results Several readily available quaternary ammonium formulations were evaluated and proved to be effective with greater than a 99.9% reduction in titer after drying on both metal and plastic surfaces. In addition, a silinated quaternary ammonium compound that left a residual on the surface was capable of inactivating SARS-CoV-2 for at least seven days after application. Studies on the finger transfer of coronavirus from various surfaces showed that the amount of virus transfer to the finger varied from 0.46 to 49.0% depending upon the surface. Little or no virus transfer occurred from treated surfaces compared to the untreated controls. In addition, coronavirus 229E appears to be a good model for use in disinfection assessments for SARS-CoV-2. Conclusion Our results demonstrate that various quaternary ammonium disinfectant formulations are effective against human coronaviruses. Finger transfer tests showed that transmission of coronavirus from surfaces can be prevented, reducing the risk of fomite transmission. Coronavirus 229E appears to be a good model for use in disinfection assessments for SARS-CoV-2. Disclosures Charles P. Gerba, Ph.D., Allied Biosciences (Grant/Research Support)Behr (Grant/Research Support)Corning Inc. (Grant/Research Support)PPG (Grant/Research Support)Procter and Gamble (Other Financial or Material Support, donation)Rickett and Coleman (Grant/Research Support)

Endocytosis and Transcytosis of SARS-CoV-2 Across the Intestinal Epithelium and Other Tissue Barriers

Since 2003, the world has been confronted with three new betacoronaviruses that cause human respiratory infections: SARS-CoV, which causes severe acute respiratory syndrome (SARS), MERS-CoV, which causes Middle East respiratory syndrome (MERS), and SARS-CoV-2, which causes Coronavirus Disease 2019 (COVID-19). The mechanisms of coronavirus transmission and dissemination in the human body determine the diagnostic and therapeutic strategies. An important problem is the possibility that viral particles overcome tissue barriers such as the intestine, respiratory tract, blood-brain barrier, and placenta. In this work, we will 1) consider the issue of endocytosis and the possibility of transcytosis and paracellular trafficking of coronaviruses across tissue barriers with an emphasis on the intestinal epithelium; 2) discuss the possibility of antibody-mediated transcytosis of opsonized viruses due to complexes of immunoglobulins with their receptors; 3) assess the possibility of the virus transfer into extracellular vesicles during intracellular transport; and 4) describe the clinical significance of these processes. Models of the intestinal epithelium and other barrier tissues for in vitro transcytosis studies will also be briefly characterized.

Transfer rate of enveloped and non-enveloped 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 handwash, 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) and MS2 (a surrogate for non-enveloped 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 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 which 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 modelling the distribution of enveloped and non-enveloped virus transfer rates, which can aid in the implementation of risk assessment models in the future. Additionally, enveloped and non-enveloped 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 handwash, 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.

Comparison of the Efficacy of Disinfectant Pre-impregnated Wipes for Decontaminating Stainless Steel Carriers Experimentally Inoculated With Ebola Virus and Vesicular Stomatitis Virus

The authors evaluated four disinfectant pre-impregnated wipes (DPW) for efficacy against Ebola virus Makona variant (EBOV) and vesicular stomatitis virus (VSV), Indiana serotype. Steel carriers were inoculated with the infectious virus and then were wiped with DPW in the Wiperator instrument per ASTM E2967-15. Following the use of J-Cloth impregnated with medium (negative control wipes) or the use of activated hydrogen peroxide (AHP)-, ethanol-, sodium hypochlorite (NaOCl)-, or single or dual quaternary ammonium compound (QAC)-based DPW, virus recovery from the carriers was assayed by titration assay and by two passages on Vero E6 cells in 6-well plates. The Wiperator also enabled the measurement of potential transfer of the virus from the inoculated carrier to a secondary carrier by the DPW or control wipes. The J-Cloth wipes wetted with medium alone (no microbicidal active) removed 1.9–3.5 log10 of virus from inoculated carriers but transferred ~4 log10 of the wiped virus to secondary carriers. DPW containing AHP, ethanol, NaOCl, or single or dual QAC as active microbicidal ingredients removed/inactivated ~6 log10 of the virus, with minimal EBOV or no VSV virus transfer to a secondary surface observed. In Ebola virus outbreaks, a DPW with demonstrated virucidal efficacy, used as directed, may help to mitigate the unintended spread of the infectious virus while performing surface cleaning.

Transfer rate of enveloped and non-enveloped 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 handwash, 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) and MS2 (a surrogate for non-enveloped 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 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 which can be used to refine quantitative microbial risk assessments. This study is the first to provide 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.

DC/L-SIGN recognition of spike glycoprotein promotes SARS-CoV-2 trans-infection and can be inhibited by a glycomimetic antagonist

The efficient spread of SARS-CoV-2 resulted in a unique pandemic in modern history. Despite early identification of ACE2 as the receptor for viral spike protein, much remains to be understood about the molecular events behind viral dissemination. We evaluated the contribution of C-type lectin receptors (CLRS) of antigen-presenting cells, widely present in respiratory mucosa and lung tissue. DC-SIGN, L-SIGN, Langerin and MGL bind to diverse glycans of the spike using multiple interaction areas. Using pseudovirus and cells derived from monocytes or T-lymphocytes, we demonstrate that while virus capture by the CLRs examined does not allow direct cell infection, DC/L-SIGN, among these receptors, promote virus transfer to permissive ACE2+ Vero E6 cells. A glycomimetic compound designed against DC-SIGN, enable inhibition of this process. These data have been then confirmed using authentic SARS-CoV-2 virus and human respiratory cell lines. Thus, we described a mechanism potentiating viral spreading of infection.

Metatranscriptomic Identification of Diverse and Divergent RNA Viruses in Green and Chlorarachniophyte Algae Cultures

Our knowledge of the diversity and evolution of the virosphere will likely increase dramatically with the study of microbial eukaryotes, including the microalgae within which few RNA viruses have been documented. By combining total RNA sequencing with sequence and structural-based homology detection, we identified 18 novel RNA viruses in cultured samples from two major groups of microbial algae: the chlorophytes and the chlorarachniophytes. Most of the RNA viruses identified in the green algae class Ulvophyceae were related to the Tombusviridae and Amalgaviridae viral families commonly associated with land plants. This suggests that the evolutionary history of these viruses extends to divergence events between algae and land plants. Seven Ostreobium sp-associated viruses exhibited sequence similarity to the mitoviruses most commonly found in fungi, compatible with horizontal virus transfer between algae and fungi. We also document, for the first time, RNA viruses associated with chlorarachniophytes, including the first negative-sense (bunya-like) RNA virus in microalgae, as well as a distant homolog of the plant virus Virgaviridae, potentially signifying viral inheritance from the secondary chloroplast endosymbiosis that marked the origin of the chlorarachniophytes. More broadly, these data suggest that the scarcity of RNA viruses in algae results from limited investigation rather than their absence.