New Delhi: When the Covid pandemic hit in early 2020, health agencies around the world came out with preventive guidelines emphasizing the need to disinfect surfaces, leading to a rigorous disinfection campaign.
There was widespread belief that surfaces contained infectious germs or germs and that one could contract COVID-19 by touching them.
However, by early 2021, scientific evidence Started pointing to the fact that COVID is more likely to spread through air than surface or fomite contact.
Soon, the World Health Organization (WHO) and the US Centers for Disease Control and Prevention (CDC) both accepted the aerosol theory, which meant you were more likely to get COVID-19 if you spoke to a carrier. Is. Public lift button.
A recent study by the US National Institutes of Health (NIH), which compared the effects of transmission via different routes, has now found that air transmission is more “efficient” than fomite (surface) transmission.
Studies on Syrian hamsters show that airborne transmission is also associated with greater severity of the disease.
The NIH study, published in the journal Nature Communications, said, “Given the scale of the COVID-19 pandemic, it is unclear to what extent the different routes of exposure contribute to human-to-human transmission and the extent to which exposure routes contribute to disease expression.” How does it affect? Week.
The study was conducted by scientists from NIH’s National Institute of Allergy and Infectious Diseases, and they used different mechanisms of exposure, such as intranasal inoculation and aerosol and fomite exposure techniques, to determine the severity of the disease associated with each pathway.
The SARS-CoV-2 vaccine was administered to Syrian hamsters aged four to six years. One part of the study was to examine how different exposure routes affected disease development, and the other part was comparing between animal-to-animal transmission of the virus by the airborne system and in infected cage environments or fomites.
Airborne and fomite transmission route experiments
Four animals were housed together for the experiment. The droplets were loaded with the SARS-CoV-2 virus in aerosol exposure, and the hamsters were exposed to them for ten minutes. Then, the volume of the inoculum (the ability of a pathogen or its organs to cause infection in an organism) is determined by the animal’s respiratory minute volume rate, which is the amount of breath in or out of an animal’s lungs per minute. is the amount of gas. .
Equal numbers of infected and non-infected hamsters were placed on either side of the same cage, with a divider between them. This was to prevent direct contact between infected (donor) hamsters and non-infected (sentinel/recipient) hamsters. Intranasal inoculation was used to infect the donor hamster. The study report noted that normal airflow conditions were allowed within the cage, either directing the airflow from the donor to the sentinel.
A SARS-CoV-2 contaminated dish was placed in animal cages. Two animals were housed in a cage for four days and exposed to fomite.
Air was made to flow at a constant rate, and an inlet was introduced on the side of the infected hamster with sampling ports at each end of the cage. The system was meant to measure virus-laden droplets in the air. After the hamsters were infected, swabs were collected from the animals and the cage. Viral load was calculated from the standard curve.
What did the scientist discover?
It was found that there is a direct relationship between disease severity and exposure pathway. Exposure to aerosols caused the SARS-CoV-2 virus to accumulate deep in the lungs, while exposure to fomites caused the virus to replicate initially in the nose and later in the lungs.
The severity of lung damage was higher in aerosol exposure than in fomite exposure. Aerosol exposure resulted in weight loss, whereas fomite exposure caused mild respiratory pathology, and delayed viral shedding patterns (the release of virus progeny after reproduction in the infected host cell). The onset of viral shedding affects the severity of the disease.
The study found that aerosol exposure caused virus accumulation and increased replication in the upper and lower respiratory tracts, while less severe lung pathogenesis in the respiratory tract and delayed replication in the respiratory system, as the study found .
Furthermore, the immune response in the lungs, which is a measure of cytokine production, is lower in exposure to fomite. Early shedding patterns help predict disease severity and the associated immune response. It was also found that air transmission in Syrian hamsters is more efficient than fomite transmission.
This suggests that airborne droplets are an important SARS-CoV-2 transmission route. When the airflow is directed from the donor to the sentinel, the transmission efficiency is higher than in the case where the airflow is reversed. Thus, airborne transmission is dependent on the direction of airflow.
Since SARS-CoV-2 is a rapidly evolving virus, its mechanisms of infecting host cells keep on changing. Therefore, the scientists suggested, COVID transmission models should be carefully designed so that they can be used to assess the patterns of infection.
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