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COVID-19: Transmission

by Sean Elliott, MD

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    00:01 COVID-19 Transmission.

    00:04 The SARS Coronavirus II, the cause of the infection we know of, as COVID-19, typically is transmitted via two routes.

    00:12 The first, respiratory droplets or large droplets, which travel less than two meters from the infected person and then airborne droplets or airborne spread, which, are much smaller a longer lasting and freer floating particles, which, can travel far further from the infected individual.

    00:30 Far less common, will be, fecal-oral transmission, this may be due to large respiratory droplets.

    00:36 Which are ingested and then excreted via faeces or even aerosolized faeces and potentially certainly through saliva.

    00:46 Highly unlikely, but yet rarely documented, is vertical transmission so from mother to new-born child.

    00:52 Here though, it is unclear that transmission actually occurs via the placenta, rather, it is likely that the infected mother transmits, via droplets whether respiratory or airborne to her new-born child and then causes the apparent vertical infection.

    01:10 Very unlikely but still unfortunately possible, is transmission via contaminated surfaces.

    01:16 And this again, has to do with those large respiratory droplets, which take longer to dry out.

    01:22 Dried droplets, of course are going to be noxious to the virus itself, it cannot survive. So, a remaining moist droplet, which then is picked up via a hand typically, a soiled hand, can then transmit to a mucous membrane.

    01:38 Such as, resting one's hand on the bedside table, of an infected COVID-19 patient and then touching one's eyes or mouth or nose.

    01:49 So, it is unfortunate, that this virus is so infectious because it is also quite deadly and in fact, in both these entities infectivity and mortality, it is far worse than influenza virus, which we know causes an annual epidemic of disease.

    02:07 Why is this so? Well, there are there are features involving, asymptomatic but infected individuals, in whom, the viral loads peak well before symptom onset.

    02:20 So, that means that the individual who is infected and is either asymptomatic completely or pre-symptomatic, will still have a high viral load expressed in their respiratory droplets and thus, be quite contagious.

    02:34 As well, asymptomatic and symptomatic patients all transmit the same high viral loads for the same length of time.

    02:43 So, unfortunately, the symptom onset which most of us use as an indicator to self-isolate or put on gloves or a mask, is unfortunately not the indicator, that we think that it could be.

    02:56 The other difference however, is that, evolving variants or mutant variants of the SARS Coronavirus II, are having increased infectivity for example, the delta variant the B.1.618.2 is 50% or even 55% more infectious, than the original variant of the D614G and perhaps even more infectious than the alpha very the B1117.

    03:27 So, what is likely happening is that, mutations in the spike protein the s protein, allow the virus to bind more strongly to its receptors and then to create a higher viral load.

    03:41 So, as always, and especially in the setting of this particular virus, the science surrounding what we know about transmission virus, continues to evolve as does the virus itself.

    03:54 Nature is quite active and as further variants and mutant variants emerge, so too will our understanding of this particular virus and how contagious it might be.


    About the Lecture

    The lecture COVID-19: Transmission by Sean Elliott, MD is from the course Coronavirus.


    Included Quiz Questions

    1. When viral load peaks, which may be before symptoms appear
    2. About 10 days after symptoms appear
    3. After about a week of symptoms
    4. After 3 to 5 days of symptoms
    5. On the first day that symptoms appear
    1. India
    2. China
    3. Italy
    4. England
    5. United States

    Author of lecture COVID-19: Transmission

     Sean Elliott, MD

    Sean Elliott, MD


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