Browsing by Author "Lakdawala, Seema S."

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    Environmental Persistence of Influenza Viruses Is Dependent upon Virus Type and Host Origin
    Kormuth, Karen A.; Lin, Kaisen; Qian, Zhihong; Myerburg, Michael M.; Marr, Linsey C.; Lakdawala, Seema S. (American Society for Microbiology, 2019-08-21)
    Highly transmissible influenza viruses (IV) must remain stable and infectious under a wide range of environmental conditions following release from the respiratory tract into the air. Understanding how expelled IV persist in the environment is critical to limiting the spread of these viruses. Little is known about how the stability of different IV in expelled aerosols is impacted by exposure to environmental stressors, such as relative humidity (RH). Given that not all IV are equally capable of efficient airborne transmission in people, we anticipated that not all IV would respond uniformly to ambient RH. Therefore, we have examined the stability of human-pathogenic seasonal and avian IV in suspended aerosols and stationary droplets under a range of RH conditions. H3N2 and influenza B virus (IBV) isolates are resistant to RH-dependent decay in aerosols in the presence of human airway surface liquid, but we observed strain-dependent variations in the longevities of H1N1, H3N2, and IBV in droplets. Surprisingly, low-pathogenicity avian influenza H6N1 and H9N2 viruses, which cause sporadic infections in humans but are unable to transmit person to person, demonstrated a trend toward increased sensitivity at midrange to high-range RH. Taken together, our observations suggest that the levels of vulnerability to decay at midrange RH differ with virus type and host origin.
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    Environmental Stability of Enveloped Viruses Is Impacted by Initial Volume and Evaporation Kinetics of Droplets
    French, Andrea J.; Longest, Alexandra K.; Pan, Jin; Vikesland, Peter J.; Duggal, Nisha K.; Marr, Linsey C.; Lakdawala, Seema S. (American Society for Microbiology, 2023-04)
    Efficient spread of respiratory viruses requires the virus to maintain infectivity in the environment. Environmental stability of viruses can be influenced by many factors, including temperature and humidity. Our study measured the impact of initial droplet volume (50, 5, and 1 mu L) and relative humidity (RH; 40%, 65%, and 85%) on the stability of influenza A virus, bacteriophage Phi6 (a common surrogate for enveloped viruses), and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) under a limited set of conditions. Our data suggest that the drying time required for the droplets to reach quasi-equilibrium (i.e., a plateau in mass) varied with RH and initial droplet volume. The macroscale physical characteristics of the droplets at quasi-equilibrium varied with RH but not with the initial droplet volume. Virus decay rates differed between the wet phase, while the droplets were still evaporating, and the dry phase. For Phi6, decay was faster in the wet phase than in the dry phase under most conditions. For H1N1pdm09, decay rates between the two phases were distinct and initial droplet volume had an effect on virus viability within 2 h. Importantly, we observed differences in virus decay characteristics by droplet size and virus. In general, influenza virus and SARS-CoV-2 decayed similarly, whereas Phi6 decayed more rapidly under certain conditions. Overall, this study suggests that virus decay in media is related to the extent of droplet evaporation, which is controlled by RH. Importantly, accurate assessment of transmission risk requires the use of physiologically relevant droplet volumes and careful consideration of the use of surrogates. IMPORTANCE During the COVID-19 pandemic, policy decisions were being driven by virus stability experiments with SARS-CoV-2 in different droplet volumes under various humidity conditions. Our study, the first of its kind, provides a model for the decay of multiple enveloped RNA viruses in cell culture medium deposited in 50-, 5-, and 1-mu L droplets at 40%, 65%, and 85% RH over time. The results of our study indicate that determination of half-lives for emerging pathogens in large droplets may overestimate transmission risk for contaminated surfaces, as observed during the COVID-19 pandemic. Our study implicates the need for the use of physiologically relevant droplet sizes with use of relevant surrogates in addition to what is already known about the importance of physiologically relevant media for risk assessment of future emerging pathogens.
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    Influenza Virus Infectivity Is Retained in Aerosols and Droplets Independent of Relative Humidity
    Kormuth, Karen A.; Lin, Kaisen; Prussin, Aaron J. II; Vejerano, Eric P.; Tiwari, Andrea J.; Cox, Steve S.; Myerburg, Michael M.; Lakdawala, Seema S.; Marr, Linsey C. (Oxford University Press, 2018-06-07)
    Pandemic and seasonal influenza viruses can be transmitted through aerosols and droplets, in which viruses must remain stable and infectious across a wide range of environmental conditions. Using humidity-controlled chambers, we studied the impact of relative humidity on the stability of 2009 pandemic influenza A(H1N1) virus in suspended aerosols and stationary droplets. Contrary to the prevailing paradigm that humidity modulates the stability of respiratory viruses in aerosols, we found that viruses supplemented with material from the apical surface of differentiated primary human airway epithelial cells remained equally infectious for 1 hour at all relative humidities tested. This sustained infectivity was observed in both fine aerosols and stationary droplets. Our data suggest, for the first time, that influenza viruses remain highly stable and infectious in aerosols across a wide range of relative humidities. These results have significant implications for understanding the mechanisms of transmission of influenza and its seasonality.
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    Mechanistic insights into the effect of humidity on airborne influenza virus survival, transmission and incidence
    Marr, Linsey C.; Tang, Julian W.; Van Mullekom, Jennifer H.; Lakdawala, Seema S. (Royal Society Publishing, 2019-01-16)
    Influenza incidence and seasonality, along with virus survival and transmission, appear to depend at least partly on humidity, and recent studies have suggested that absolute humidity (AH) is more important than relative humidity (RH) in modulating observed patterns. In this perspective article, we re-evaluate studies of influenza virus survival in aerosols, transmission in animal models and influenza incidence to show that the combination of temperature and RH is equally valid as AH as a predictor. Collinearity must be considered, as higher levels of AH are only possible at higher temperatures, where it is well established that virus decay is more rapid. In studies of incidence that employ meteorological data, outdoor AH may be serving as a proxy for indoor RH in temperate regions during the wintertime heating season. Finally, we present a mechanistic explanation based on droplet evaporation and its impact on droplet physics and chemistry for why RH is more likely than AH to modulate virus survival and transmission.
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    SARS-CoV-2 indoor air transmission is a threat that can be addressed with science
    Samet, Jonathan M.; Burke, Thomas A.; Lakdawala, Seema S.; Lowe, John L.; Marr, Linsey C.; Prather, Kimberly A.; Shelton-Davenport, Marilee; Volckens, John (National Academies of Sciences, 2021-11-02)
    The Environmental Health Matters Initiative (EHMI) of the National Academies of Science, Engineering, and Medicine (NASEM) was established by the three presidents as a mechanism for a transformational cross-institutional approach to enable challenges to be informed—rapidly if needed—by insights from a broad range of applicable scientific disciplines and sectors spanning academia, government, foundations, businesses, and nongovernmental organizations. The EHMI reaches across the three National Academies to provide a venue for bringing transdisciplinary and cross-sector thinking to environmental health issues that are urgent, on the horizon, or recalcitrant in nature. This paper describes how EHMI approached the critical and extremely vexing problem of the airborne transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) as the pandemic reached the six-month mark in the United States.
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    Toward a Mechanistic Understanding of Inactivation of Respiratory Viruses in the Environment
    Longest, Alexandra Kennedy (Virginia Tech, 2025-01-03)
    Airborne transmission of most respiratory viruses was not widely acknowledged until the COVID-19 pandemic. For viruses to transmit between infected and healthy individuals, they must remain stable (i.e., "survive") in aerosols and droplets. Their stability is influenced by many factors including temperature, relative humidity (RH), physico-chemical properties of the carrier droplet, and virus strain. However, the exact mechanisms of viral inactivation remain unknown. The primary aim of this work was to delineate the complex interactions occurring within aerosols and droplets and the mechanisms that drive inactivation of viruses within them. Initially, we reviewed and synthesized existing studies on aerosols and droplets to identify knowledge gaps regarding these mechanisms. This system is highly complex, with various factors influencing viral stability interacting with each other. We recommend that future studies focus on more physiologically relevant aerosol and droplet sizes and fluids to better understand this system in real-world contexts. As previous studies often used large droplets, we shifted our focus to the environmental stability of enveloped viruses (Phi6, influenza virus, and SARS-CoV-2) as a function of initial droplet size (50, 5, and 1 µL) and evaporation kinetics. Our findings indicated that RH had a greater impact on viral decay in large droplets compared to small droplets, and in addition, suggested caution when using surrogates to study the stability of pathogenic viruses. Subsequently, we explored how gas-phase composition and pH affect influenza stability by manipulating the surrounding air. Results indicated that pH has little influence on influenza virus in saliva droplets, implying that another factor may drive decay. Lastly, we examined the survival of influenza virus in the presence of reactive oxygen species (ROS) scavengers, finding that certain ROS may play a significant role in virus inactivation.