Coronaviridae: Overview

by Sean Elliott, MD

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    00:07 Coronaviridae.

    00:10 Coronaviridae are large enveloped viruses, as noted with this intracellular membrane, as you see here on this colorized transmission electrogram image.

    00:20 They contain the helical capsid.

    00:22 The appearance that you see in front of you is appears to be a corona or halo and this is due to the presence of viral spike peplomeres, which, emanate from the enveloped proteinaceous structures, giving it the appearance that you see here.

    00:38 These viruses are contain a linear single stranded, positive sense RNA genome which functions as messenger RNA.

    00:46 There are seven species of coronaviruses, known to infect humans, four of these cause typically about a third of the common colds, known to human medical science, three cause severe infections, starting in 2002/2003 with the severe acute respiratory syndrome coronavirus I, or SARS-Coronavirus I, followed about 10 years later in diagnosis by the, Middle East respiratory syndrome coronavirus MERS-Coronavirus and then of course the current concern with the severe acute respiratory syndrome coronavirus II or SARS-Coronavirus II.

    01:21 The transmission of this virus is primarily through respiratory droplets produced by coughing, sneezing or talking These droplets must directly contact the uninfected individuals mucous membranes, which limits the transmission zone to around two meters.

    01:35 Airborne transmission is caused by the aerosolization of respiratory droplets that can remain suspended in the air over time.

    01:42 This mechanism is less common and usually associated with enclosed poorly ventilated spaces.

    01:48 Other considerations include universal airborne precautions during any aerosol generating medical procedures, such as intubation Other less common modes include surface transmission, where touching a contaminated surface allows the virus to infect the individual when they subsequently touch their eyes, nose or mouth.

    02:08 The virus can remain viable on hands for up to 9 hours.

    02:11 So handwashing is extremely important.

    02:14 Non respiratory specimen transmission from stool blood products, semen or ocular secretions remain unlikely, though they cannot be definitively excluded.

    02:23 Congenital infections have been documented, but also remain very rare.

    02:28 Finally, though, the virus has been identified in several animal species, they are not considered to be a major source of infection.

    02:35 In humans The diseases caused by coronaviruses, again, are principally mild common colds, incubation period around three days, these are very common and they battle with the rhinoviruses, to cause a majority of the wintertime common colds, that we all experience.

    02:53 The prognosis of course is excellent with complete resolution typically after a week or so of symptoms.

    03:00 The clinical manifestations are sneezing, clear rhinorrhea, headache, sore throat, general malaise, low-grade fever and sometimes with chills.

    03:10 Most patients who experience the common cold are infants and young children, but of course, adults can get these as well.

    03:17 The gastrointestinal tract infections are quite rare thankfully and also have an incubation period of three days or so, again, the prognosis is excellent unless, one is very young or immunocompromised.

    03:30 Those individuals may develop necrotizing enterocolitis, likely due to an immune reaction, against the coronaviruses attached, to the gut epithelium. Clinical manifestations here again, diarrhea non-bloody, evidence of gastroenteritis, with nausea, emesis, anorexia and in young infants especially, premature, young infants, neonatal necrotizing enterocolitis.

    03:57 The SARS-Coronavirus I in 2002/2003 caused a limited epidemic, within incubation period a little bit longer, 4 to 6 days, almost a third of patients, had complete resolution of their symptoms, while 70% went on to develop severe infection.

    04:14 Of those 10% experienced a fatality.

    04:17 Here the symptoms started mild, so again, lower grade fever over 100 degrees Fahrenheit or 37.7 degrees Celsius, but then went on to develop significant muscle pain and myalgias, lethargy a dry non-productive cough, along with sore throat and significant malaise.

    04:35 Those individuals who proceeded to severe infection, then also develop shortness of breath a remarkably, not unique but important indicator of disease progression, followed by either a primary viral or a secondary bacterial pneumonia.

    04:52 These patients presented to hospital and rapidly developed, diffuse evidence of almost an ARDS, an “Acute respiratory distress syndrome,” picture on their chest x-rays.

    05:05 In 2012, cases began to emerge of Middle Eastern respiratory syndrome coronaviruses or MERS-Coronavirus, with an incubation period of two to fourteen days, very similar to what we're experiencing currently with the SARS-Coronavirus II.

    05:20 In the patients with MERS-Coronavirus, about a third died from their illness, however, most had an asymptomatic or mildly symptomatic disease, again, very similar to what we're currently experiencing with COVID-19.

    05:33 Those who had mild or even moderate symptoms, again, had low grade fevers, with a dry non-productive cough, which occasionally progressed to a wet but non-productive cough, accompanied by shortness of breath and gastrointestinal symptoms, including nausea, emesis and mild diarrhea.

    05:50 Those patients with severe disease just as with the SARS-Coronavirus I, went on to develop respiratory distress, shortness of breath and evidence of focal and bilateral pneumonia.

    06:03 Turning to the SARS-Coronavirus II, the cause of the current pandemic that we're experiencing and which started in 2019, this incubation period again 2 to 14 days, on average 4 to 5 days.

    06:16 The World Health Organization, declared a COVID-19 pandemic, on March 11 of the year 2020 and we currently have evidence of that pandemic ongoing.

    06:26 80% of patients with infection by SARS-Coronavirus II, have complete resolution and in fact many are asymptomatic, 15% develop severe infection requiring hospitalization, 5% develop critical infection, typically requiring respiratory support of some, either non-mechanical or non-invasive ventilation or invasive ventilation.

    06:50 1.2% is the mortality rate, although this does vary.

    06:55 typically depending on the age demographic, those countries with older populations, have a higher rate or higher risk of higher case fatalities.

    07:04 Clinical manifestations, as noted, many of these patients with SARS-Coronavirus II infection or COVID-19, are asymptomatic or mildly symptomatic.

    07:14 Mild symptoms are just as with the common cold, low-grade fever, dry cough, malaise, some dehydration, however, those who want to develop severe disease, will typically have elevated high fever, accompanied by shortness of breath, chest pain and hemoptysis.

    07:31 It is this specific coronavirus, which, is escalated and elevated, I should say, the coronavirus, the lowly humble coronavirus, normally thought to be the cause of the common cold to international significance due to its ability to cause, pandemics as well as localized outbreaks.

    About the Lecture

    The lecture Coronaviridae: Overview by Sean Elliott, MD is from the course Coronavirus.

    Included Quiz Questions

    1. Enveloped single-stranded RNA virus
    2. Naked double-stranded DNA virus
    3. Negative-sense single-stranded segmented RNA virus
    4. Enveloped double-stranded DNA virus
    5. Reverse transcribing virus
    1. Direct person-to-person transmission through close-range contact via respiratory particles
    2. Indirect transmission via fomites (touched surfaces)
    3. Fecal–oral transmission
    4. Direct person-to-person transmission via sexual contact
    5. Not clearly known
    1. About 1.2%
    2. About 5%
    3. About 20%
    4. About 0.5%
    5. About 10%

    Author of lecture Coronaviridae: Overview

     Sean Elliott, MD

    Sean Elliott, MD

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