Publications by authors named "Tamar Kohn"

We describe a novel biosafety aerosol chamber equipped with state-of-the-art instrumentation for bubble-bursting aerosol generation, size distribution measurement, and condensation-growth collection to minimize sampling artifacts when measuring virus infectivity in aerosol particles. Using this facility, we investigated the effect of relative humidity (RH) in very clean air without trace gases (except ∼400 ppm CO) on the preservation of influenza A virus (IAV) infectivity in saline aerosol particles. We characterized infectivity in terms of 99%-inactivation time, , a metric we consider most relevant to airborne virus transmission.

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Article Synopsis
  • Influenza A virus (IAV) spreads through exhaled droplets, and its stability is influenced by the concentration of NaCl and environmental factors during drying.
  • The study shows that IAV inactivation increases with NaCl concentration during evaporation, peaks at concentrations over 20 mol/(kg HO), and slows down significantly after efflorescence occurs.
  • Introduction of sucrose reduces IAV inactivation by lowering NaCl levels and providing protective effects, while a biophysical model accurately predicts inactivation rates based solely on NaCl molality.
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Unlabelled: The composition of respiratory fluids influences the stability of viruses in exhaled aerosol particles and droplets, though the role of respiratory organics in modulating virus stability remains poorly understood. This study investigates the effect of organic compounds on the stability of influenza A virus (IAV) in deposited droplets. We compare the infectivity loss of IAV at different relative humidities (RHs) over the course of 1 h in 1-µL droplets consisting of phosphate-buffered saline (without organics), synthetic lung fluid, or nasal mucus (both containing organics).

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Serine proteases are important environmental contributors of enterovirus biocontrol. However, the structural features of molecular interaction accounting for the susceptibility of enteroviruses to proteases remains unexplained. Here, we describe the molecular mechanisms involved in the recruitment of serine proteases to viral capsids.

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Aerosol transmission remains a major challenge for control of respiratory viruses, particularly those causing recurrent epidemics, like influenza A virus (IAV). These viruses are rarely expelled alone, but instead are embedded in a consortium of microorganisms that populate the respiratory tract. The impact of microbial communities and inter-pathogen interactions upon stability of transmitted viruses is well-characterized for enteric pathogens, but is under-studied in the respiratory niche.

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Wastewater-based epidemiology offers a complementary approach to clinical case-based surveillance of emergent diseases and can help identify regions with infected people to prioritize clinical surveillance strategies. However, tracking emergent diseases in wastewater requires reliance on novel testing assays with uncertain sensitivity and specificity. Limited pathogen shedding may cause detection to be below the limit of quantification or bordering the limit of detection.

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Viral metagenomics is a useful tool for detecting multiple human viruses in urban sewage. However, more refined protocols are required for its effective use in disease surveillance. In this study, we investigated the performance of three different preamplification pipelines (specific to RNA viruses, DNA viruses or both) for viral genome sequencing using spiked-in Phosphate Buffered Saline and sewage samples containing known concentrations of viruses.

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Article Synopsis
  • - The study investigates how specific amino acid changes in the capsid proteins of coxsackievirus B5 (CVB5) influence the virus's resistance to disinfectants like chlorine and heat treatment.
  • - It was found that while the amino acid changes did not significantly affect chlorine sensitivity, some changes at the C-terminal region of viral protein 1 reduced the virus's sensitivity to heat.
  • - Cryo-electron microscopy showed that these changes impact the virus's structure, possibly enhancing its stability and affecting how it uncoats during infection, which might explain the reduced heat sensitivity.
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Background: Temperate subalpine lakes recovering from eutrophication in central Europe are experiencing harmful blooms due to the proliferation of , a potentially toxic cyanobacteria. To optimize the management of cyanobacteria blooms there is the need to better comprehend the combination of factors influencing the diversity and dominance of cyanobacteria and their impact on the lake's ecology. The goal of this study was to characterize the diversity and seasonal dynamics of cyanobacteria communities found in a water column of Lake Geneva, as well as the associated changes on bacterioplankton abundance and composition.

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The respiratory tract of humans is constantly exposed to potentially harmful agents, such as small particles or pathogens, and thus requires protective measures. Respiratory mucus that lines the airway epithelia plays a major role in the prevention of viral infections by limiting the mobility of viruses, allowing subsequent mucociliary clearance. Understanding the interplay between respiratory mucus and viruses can help elucidate host and virus characteristics that enable the initiation of infection.

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Multiple respiratory viruses, including influenza A virus (IAV), can be transmitted via expiratory aerosol particles, and aerosol pH was recently identified as a major factor influencing airborne virus infectivity. Indoors, small exhaled aerosols undergo rapid acidification to pH ~4. IAV is known to be sensitive to mildly acidic conditions encountered within host endosomes; however, it is unknown whether the same mechanisms could mediate viral inactivation within the more acidic aerosol micro-environment.

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Human adenoviruses are ubiquitous contaminants of surface water. Indigenous protists may interact with adenoviruses and contribute to their removal from the water column, though the associated kinetics and mechanisms differ between protist species. In this work, we investigated the interaction of human adenovirus type 2 (HAdV2) with the ciliate .

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Enteroviruses, which are commonly circulating viruses shed in the stool, are released into the sewage system and only partially removed or inactivated, resulting in the discharge of infectious enteroviruses into the environment. Activated sludge and chlorination remove or inactivate enterovirus genotypes to different extents, and thus have the potential to shape the population that will be discharged. The goal of this study was to evaluate how activated sludge and chlorination treatment shape an enterovirus population at the genotype level, using a population of eight genotypes commonly found in sewage: CVA9, CVB1, CVB2, CVB3, CVB4, CVB5, E25, E30.

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Virucidal efficacies of disinfectants are typically assessed by infectivity assay utilizing a single type of host cell. Enteroviruses infect multiple host cells various entry routes, and each entry route may be impaired differently by a given disinfectant. Yet, it is unknown how the choice of host cells affects the observed inactivation kinetics.

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Respiratory viruses, including influenza virus and SARS-CoV-2, are transmitted by the airborne route. Air filtration and ventilation mechanically reduce the concentration of airborne viruses and are necessary tools for disease mitigation. However, they ignore the potential impact of the chemical environment surrounding aerosolized viruses, which determines the aerosol pH.

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Article Synopsis
  • Waterborne viruses in recreational lakes, like Lake Geneva, may threaten human health, particularly due to limited understanding of their transport and inactivation in the environment.* -
  • A model was developed to assess the movement and infection risk of four common viruses, revealing that norovirus poses the highest risk to swimmers, with infection probabilities significantly influenced by environmental factors like temperature and solar exposure.* -
  • Wind direction plays a crucial role in spreading contamination, as the study found substantial differences in infection probabilities at beaches depending on whether the wind blew eastward or westward from the sewage discharge site.*
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Wastewater-based epidemiology (WBE) has emerged as an effective tool for monitoring SARS-CoV-2 dynamics during the COVID-19 pandemic. Here, we add a spatial component to WBE and use it to investigate SARS-CoV-2 spread in the canton of Ticino during the onset of the pandemic in Switzerland (end of February 2020 to beginning of March 2020). Ticino is located at the border to Northern Italy, where a large COVID-19 outbreak occurred in February 2020.

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The continuing emergence of SARS-CoV-2 variants of concern and variants of interest emphasizes the need for early detection and epidemiological surveillance of novel variants. We used genomic sequencing of 122 wastewater samples from three locations in Switzerland to monitor the local spread of B.1.

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Inactivation kinetics of enterovirus by disinfection is often studied using a single laboratory strain of a given genotype. Environmental variants of enterovirus are genetically distinct from the corresponding laboratory strain, yet it is poorly understood how these genetic differences affect inactivation. Here we evaluated the inactivation kinetics of nine coxsackievirus B3 (CVB3), ten coxsackievirus B4 (CVB4), and two echovirus 11 (E11) variants by free chlorine and ultraviolet irradiation (UV).

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Background: The effective reproductive number, , is a critical indicator to monitor disease dynamics, inform regional and national policies, and estimate the effectiveness of interventions. It describes the average number of new infections caused by a single infectious person through time. To date, estimates are based on clinical data such as observed cases, hospitalizations, and/or deaths.

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