Influenza viruses can spread through the air on dust, fibers and other microscopic particles, according to new research from the University of California, Davis and the Icahn School of Medicine at Mt. Sinai.
The findings, with obvious implications for coronavirus transmission as well as influenza, are published Aug. 18 in Nature Communications.
“It’s really shocking to most virologists and epidemiologists that airborne dust, rather than expiratory droplets, can carry influenza virus capable of infecting animals,” said Professor William Ristenpart of the UC Davis Department of Chemical Engineering, who helped lead the research.
“The implicit assumption is always that airborne transmission occurs because of respiratory droplets emitted by coughing, sneezing, or talking.
Transmission via dust opens up whole new areas of investigation and has profound implications for how we interpret laboratory experiments as well as epidemiological investigations of outbreaks.”
Fomites and influenza virus
Influenza virus is thought to spread by several different routes, including in droplets exhaled from the respiratory tract or on secondary objects such as door handles or used tissues.
These secondary objects are called fomites. Yet little is known about which routes are the most important. The answer may be different for different strains of influenza virus or for other respiratory viruses, including coronaviruses such as SARS-CoV2.
In the new study, UC Davis engineering graduate student Sima Asadi and Ristenpart teamed up with virologists led by Dr. Nicole Bouvier at Mt. Sinai to look at whether tiny, non-respiratory particles they call “aerosolized fomites” could carry influenza virus between guinea pigs.
Using an automated particle sizer to count airborne particles, they found that uninfected guinea pigs give off spikes of up to 1,000 particles per second as they move around the cage.
Particles given off by the animals’ breathing were at a constant, much lower rate.
Immune guinea pigs with influenza virus painted on their fur could transmit the virus through the air to other, susceptible guinea pigs, showing that the virus did not have to come directly from the respiratory tract to be infectious.
Finally, the researchers tested whether microscopic fibers from an inanimate object could carry infectious viruses. They treated paper facial tissues with influenza virus, let them dry out, then crumpled them in front of the automated particle sizer.
Crumpling the tissues released up to 900 particles per second in a size range that could be inhaled, they found. They were also able to infect cells from these particles released from the virus-contaminated paper tissues.
Transmission of COVID-19: stability on Surfaces
Evidence reports that COVID-19 significantly pollutes the air and the environment from the surfaces of the environment built by aerosol flow (Dietz et al., 2020; Ong et al., 2020; Rothan and Byrareddy, 2020). Current estimates of contagion for each infected person (known as Ro) is 1.5 to 3.9 people (Du et al., 2020; Q. Li et al., 2020; Riou and Althaus, 2020), or even more 6.5 (Guo et al., 2020; Liu et al., 2020). While within the built environment it is between 5 and 14 ((Poon and Peiris, 2020; Zhang et al., 2020).
A transmissibility similar to that of other β-coronaviruses, such as SARS-CoV (Ro = 2.2-3.6) and the estimated Ro value of MERS-CoV is 2.0–6.7 (Lipsitch, 2003; Majumder et al., 2014; L. Wang et al., 2020). From some published studies, Ro are estimated for two moderately transmissible viruses, the coronaviruses of severe acute respiratory syndrome 2 to 4, Influenza A (H1N1) pdm09 1.4 to 1.6 to 2 and HIV 2 to 5, and for two highly transmissible viruses, smallpox Ro 4-10 and measles 12-18 (Baldo et al., 2016; Fraser et al., 2004).
It is concluded then that since the beginning of the epidemic the Ro is 2.38 and according to some current studies up to 5.7 (Li et al., 2020; Wu et al., 2020), which indicates that the SARS-CoV-2 has a relatively high sustained transmissibility.
SARS-CoV-2 is reported to be even more contagious (but thankfully less fatal) than SARS-CoV. The virus has intermediate levels of both respiratory and fecal-oral transmission potential according to a model that measures the percentage of intrinsic disorder (PID) of membrane (M) and nucleocapsid (N) proteins in viruses (Goh et al., 2012, 2020a).
The main tool uses AI technology to recognize the intrinsic disorder, given the protein sequence. The model is based on the premise that viruses that remain in hostile environments require harder, that is, less disordered, shells to survive (Goh et al., 2019).
Furthermore, higher levels of inner layer disorder could be associated with higher infectivity, especially with respect to viruses with high potential for respiratory transmission (Goh et al., 2020b, 2020c, 2013).
Evidence of the protective role of outer shells is seen in a wide variety of viruses. Sexually transmitted viruses (eg, HIV, HSV-2, HCV) have PID from the upper outer layer (Goh et al., 2019, 2020b, 2015; Goh et al., 2019).
Also, viruses that are known to last a long time in the environment, such as smallpox virus, have low outer layer PID. SARS-CoV-2 is very rare with one of the hardest outer protective layers (PID M = 6%) among coronaviruses (Goh et al., 2020a).
It is likely that this peculiarity is responsible for its high level of contagion, since the hardness of its outer layer could provide the virus with greater resistance to conditions outside the body and in body fluid, since the harder layer will better protect the virion from damage.
As a result of the hostile environment and the action of digestive enzymes found in body fluids. The ability of SARS-CoV-2 to remain infectious outside the body for a longer period than SARS-CoV could mean that it requires fewer viral particles for greater chances of infection.
As a result, the infected body is likely to be able to remove more infectious particles that are more likely to infect a person throughout their life. All of this may explain not only the high spread of COVID-19 but also the reported ability of this virus to spread even before the patient begins to show symptoms.
The mechanism by which the virus acquires increased virulence through inner coat disorder arises from the ability of the viral protein to bind promiscuously to the host protein. This ability provides rapid replication of viral proteins and particles (Goh et al., 2019, 2020b, 2020a, 2020c, 2016).
The stability of viruses in the environment is essential in risk analysis. Temperature has been the most studied factor and is recognized as the most influential.
The high temperature causes a faster viral inactivation, the opposite happens with the low temperature, viruses can survive for long periods of time (Dublineau et al., 2011; Pinon and Vialette, 2018).
The virus transmitted by blood and body fluids such as the human immunodeficiency virus (HIV) has the potential to be used as a vector, surrounded by a high organic load and its sliding envelope, which protects the internal viral components from the effects of dehydration and that carries a high potential to remain viable for long periods.
Persistence of HIV on a glass surface from 30 to 35 hours up to broader ranges of 4-8 weeks and survival of HIV for several days in stored refrigerated or non-refrigerated corpses are reported. There is a substantial loss of endogenous infectious virus in plasma samples at room temperature for more than 3 h or a few after venipuncture.
The environmental survival of viruses is particularly affected by relative humidity and can vary considerably. Despite its long survival time, there is no known evidence that HIV can be transmitted through contaminated fomites, although the possibility of such risk cannot be excluded (Valtierra, 2008; Van Bueren et al., 1994).
Some other viruses are easily transmitted through the aerosol route such as influence virus and coronavirus, their persistence as infectious potential is stable in fine aerosols for prolonged periods of time.
This stability is affected by exposure to environmental stressors, such as relative humidity. Specifically for the Influenza virus, the potential to persist on surfaces for hours in physiological drops depends on relative humidity (RH), low RH, and high RH in cool, dry, or wet and rainy conditions, facilitating virus survival, and the intermediate RH decreases the stability of the virus.
Minor fluctuations in temperature, pH and salinity improve or reduce stability and its transmission. Colder temperatures improve virus survival and transmission.
There is a significant interaction between particulate matter and mean temperature, while the relationship between ozone level and influenza incidence was independent of temperature (Kormuth et al., 2019; Sooryanarain and Elankumaran, 2015; Xu et al., 2013).
Influenza viruses can survive for approximately 24 to 72 hours on hard non-porous surfaces such as stainless steel and plastic, and up to 12 hours on porous surfaces such as cloth and paper at 28 ° C and humidity levels of 35% to 40% As well as banknotes, it has a viability that ranges from two hours to five days.
The influenza virus has been found in more than 50% of fomites and hands in contact on different surfaces in homes and daycare centers (Valtierra, 2008; World Health Organization, 2017).
Transmission of COVID-19 by air occurs in 2 different ways and requires no physical contact: droplet sprays produced by coughing, sneezing, or speaking (vocalization emits an imperceptible aerosol “cloud”) that directly impact a subject susceptible to or lodged on a surface or by inhaling aerosols with viral particles that can last in the air for hours (Asadi et al., 2020; N. Zhu et al., 2020).
A report demonstrated the presence of SARS-CoV-2 virus particles in ventilation systems in a hospital serving patients with COVID-19. Finding virus particles in these systems is more consistent with the hypothesis of the existence of a turbulent gas cloud as a means of transmission of the disease with respect to COVID-19 (Bourouiba, 2020; Ong et al., 2020); therefore, WHO advises healthcare personnel and anyone to keep a distance of 3 feet (1 m) and 6 feet from an infected person (WHO, 2020b).
The Center for Disease Control and Prevention recommends a 6 foot (2 m) gap. However, these distances do not estimate the time scale and persistence over which the cloud travels and its pathogenic load, thus generating an underestimated range of potential exposure for a health worker or healthy person.
Protective and source control masks, as well as other protective equipment, must have the ability to repeatedly resist the type of turbulent gas cloud that can be expelled during a sneeze or cough and virus exposure (Bourouiba, 2020).
The built environment serves as a contact vector of the surfaces for COVID-19 infection, since the virus can survive for hours on surfaces like fomites, but a simple disinfectant can eliminate it (Lai et al., 2020).
The literature indicates that coronaviruses can remain for hours or days according to the physical characteristics of the surfaces: plastic surfaces 6.8 hours (half-life = 15.9 h), copper (3.4 h), cardboard (8.45 h) and stainless steel 5.6 hours (half-life = 13.1 h) and shorter in aerosol form 1.1 to 1.2 hours (2.7 h); however, aerosol survival was determined at 65% relative humidity (Kampf et al., 2020; van Doremalen et al., 2020). The COVID-19 virus does not resist temperatures above 26 ° C, but can survive for approximately 5-10 minutes on the skin, six to 12 hours in plastic materials, 12 hours in metal (Nazari Harmooshi et al., 2020).
Likewise, the faecal-oral route is reported as a probable route of transmission of the virus, since it is present in the faeces (Xiao et al., 2020).
Precautions to take to slow the spread of COVID-19 infection include: washing hands for at least 20-30 seconds with soap and water or 60-80% alcohol-based hand sanitizers and implementing cleaning protocols for surfaces by chemical deactivation of viral particles (Kampf et al., 2020; Ong et al., 2020).
Transmission of aerosol SARS-CoV-2 is well documented, while transmission through fomites via abiotic surfaces via the fecal-oral route; however these mechanisms need to be considered.
The social distancing and confinement policies currently implemented given the spatial dynamics of the spread of the SARS-CoV-2 virus are of vital importance; however other less well-known routes of transmission will have to be considered and addressed to reduce the spread of this virus, especially the measures that must be taken during the stay within areas of the built environment.
Environmental factors and their influence on COVID-19 infection
Air quality
Beyond the effects of social distancing, the COVID-19 pandemic shows a way to achieve positive environmental change. The reduction of greenhouse gas emissions is identified, due to the decline in industrial activity and refineries; as well as the use of vehicles and transportation systems decreased considerably (He et al., 2020).
In Asia, Europe and America, air pollution levels are reported to be declining in several cities, specifically concentrations of nitrogen dioxide (NO2), particulate matter less than 2.5 μm in diameter (PM), black carbon (CN) . In addition, a reduction in PM10 (−28 to −31.0%) and an increase in ozone (O3) concentrations of around 50% were observed (Tobías et al., 2020).
NASA satellites and of the Copernicus Atmosphere Monitoring Service of the European Space Agency (ESA) have documented significant reduction in air pollution in major cities around the world.
It is predicted that during 2 months of improving air quality in China alone, thousands of children and older adults could be saved. A similar 20-30% reduction in pollution in the world’s major cities could generate significant health benefits (Dutheil et al., 2020; Nelson, 2020).
Given the magic and illusion of the positive environmental effects of COVID 19 that could be perceived, there is also the counterpart. As the economy reopens, curbing polluting activities and the emission of greenhouse gases and particles associated with respiratory illness, these will have a long-term negative impact from the Covid-19 pandemic in large cities.
COVID-19 and Atmospheric particles
There is scientific evidence that exposes a high correlation between the presence of ozone (O3), sulfur dioxide (SO2), nitrogen dioxide (NO2) and fine particles in the induction of hyperexpression of proinflammatory interleukins (Kurai et al., 2018; Perret et al., 2017). NO2 is a common marker of air pollution/industrial activity, associated with morbidity and mortality (He et al., 2020).
Individuals of any age group, including healthy people who are in areas with high levels of long-term air pollution, are at increased risk of developing chronic and infectious respiratory diseases.
Fine particles 2.5 mm in diameter (PM 2.5) suspended in the air have a greater possibility of entering the lower respiratory tract, leading to the development of a progressive and chronic inflammatory stimulus characterized by excessive mucus production and dysfunction of the ciliary epithelium (first defense mechanism in the respiratory tract) and induce persistent modifications of the immune system, which makes individuals more likely to develop severe respiratory diseases and viral infections (Yu Cao et al., 2020; Conticini et al., 2020; Martelletti and Martelletti, 2020; Tsai et al., 2019).
It has been hypothesized that the SARS-COV-2 virus has the ability to bind to PM and in conditions of atmospheric stability improves its persistence in the atmosphere, due to the presence of RNA from this virus in said particles, promoting its diffusion through the air (McNeill, 2020), since the role of short-term exposure with PM and transmission of COVID-19 has been reported (Y. Zhu et al., 2020); however, a study in Italy reports that the PM concentration and cases of COVID-19 virus infection are not evident, therefore it is not possible to conclude that the diffusion mechanism of COVID-19 also occurs through the air, using PM as a carrier (Bontempi, 2020; Setti et al., 2020).
However, the evaluation of PM as a chronic stressor that makes the population more vulnerable to an epidemic has been reinforced by multiple studies. Chronic exposure to air pollutants may represent a risk factor in determining the severity of Covid-19 syndrome and the high incidence of fatal events (N. Chen et al., 2020; Dutheil et al., 2020; D. Wang et al., 2020; F. Wu et al., 2020).
A correlation is reported between the high level of contamination (particles with an exposure diameter less than 2.5μm (PM 2.5) and the case fatality rate in northern Italy (Conticini et al., 2020).
While the chronicity of Exposure of atmospheric pollutants NO2, O3, PM 2.5 and PM10 were significantly correlated with the spread of cases (mortality) of the Covid-19 virus in provinces in Italy, the mortality rate varied from 18% (Fattorini and Regoli, 2020).
This allows us to conclude that there are still studies to establish the factors that affect the routes of diffusion and transmission of the SARS-COV-2 virus, such as the evaluation of the geophysical and climatic characteristics of the study areas and the relationship between the dynamics of the populations and their relationship with atmospheric pollutants.
Although, the information provided by these studies on the correlation between exposure to particles derived from air pollution, it is a priority to consider the impact that respiratory involvement brings on long-term COVID-19 infection, towards the prevalence of infections and chronic inflammatory processes; these implications need to be determined for the proposal of a future environmental policy.
An unexpected advantage may be provided to help understand how environmental health can be altered, through better environmental regulation from technology. A special consideration in the future will be the identification of the effects of the reduction of air pollution from the different emission sources that will be a starting point to evaluate other air quality policies.
Climate indicators and COVID-19
In particular, in addition to person-to-person transmission, weather parameters (temperature, wind speed and humidity) are classified as the main predictors of infectious respiratory diseases according to the viability, transmission and range of spread of the virus.
This reveals a possible association between the accumulation of atmospheric pollutants and the combination of specific weather factors that promote a greater permanence of viral particles in the air and their diffusion, specifically for infection by COVID-19 (Frontera et al., 2020; van Doremalen et al., 2020).
Ambient temperature and air quality have been estimated to be correlated with the spread of COVID-19. The mean temperature is related to the high risk of virus transmission (with a threshold of 3 ° C, when the temperature is <3 ° C) (Tosepu et al., 2020; Xie and Zhu, 2020).
A limited number of studies have shown that humidity and temperature likely affect COVID-19 activity and transmissibility (Nazari Harmooshi et al., 2020).
In Hubei province in China, low relative humidity and daytime temperature were found to have a greater impact on COVID-19 infection, while extreme daily temperature negatively influenced this virus (Liu et al., 2020; Pirouz et al., 2020).
When talking about COVID-19 mortality, weather conditions could also contribute to the decline. In Wuhan, China, temperature variation, humidity, and wind speed were reported to influence COVID-19 case fatality and number (Chen et al., 2020; Şahin, 2020).
Decreasing one unit in the daytime temperature range increases the risk of COVID-19 cases and deaths by 2.92 times. On the other hand, the increase of 1 unit of temperature as the absolute humidity were related to the decrease in death from this virus (Ma et al., 2020). Therefore, increased mortality from COVID-19 may also be related to lower humidity in winter.
Following the analysis of associations between weather conditions, air pollution and COVID-19 infection, related theories are proposed in the population distribution and the presence of the disease.
Some researchers propose that the epidemic could gradually decrease as a result of rising temperatures in the coming months. While others suggest the possibility of this disease becoming seasonal during the autumn-winter months (Hellewell et al., 2020; Maier and Brockmann, 2020).
Meanwhile, it is imperative to further strengthen prevention measures against potential transmission; therefore, strict compliance with confinement, hand washing and personal hygiene is necessary to record a lower incidence of COVID-19 and mortality.
reference link : https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7426221/
More information: Sima Asadi et al, Influenza A virus is transmissible via aerosolized fomites, Nature Communications (2020). DOI: 10.1038/s41467-020-17888-w
