Coronaviridae are large enveloped viruses,
as noted with this intracellular membrane,
as you see here on this colorized
transmission electrogram image.
They contain the helical capsid.
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
giving it the appearance that you see here.
These viruses are contain
a linear single stranded,
positive sense RNA genome which
functions as messenger RNA.
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
and then of course the current concern with the
severe acute respiratory syndrome
coronavirus II or SARS-Coronavirus II.
The transmission of this virus
is primarily through respiratory droplets
produced by coughing, sneezing or talking
must directly contact the uninfected
individuals mucous membranes,
which limits the transmission zone
to around two meters.
Airborne transmission is caused by
the aerosolization of respiratory droplets
that can remain suspended
in the air over time.
This mechanism is less common
and usually associated
with enclosed poorly ventilated spaces.
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.
The virus can remain viable on hands
for up to 9 hours.
So handwashing is extremely important.
Non respiratory specimen transmission
from stool blood products, semen or ocular
secretions remain unlikely, though
they cannot be definitively excluded.
Congenital infections have been
documented, but also remain very rare.
the virus has been identified in several
animal species, they are not considered
to be a major source of infection.
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.
The prognosis of course is excellent with complete
resolution typically after
a week or so of symptoms.
The clinical manifestations
are sneezing, clear rhinorrhea,
headache, sore throat, general malaise,
low-grade fever and sometimes with chills.
Most patients who experience the common cold
are infants and young children,
but of course, adults can get these as well.
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.
Those individuals may develop
likely due to an immune reaction,
against the coronaviruses attached,
to the gut epithelium.
Clinical manifestations here again,
evidence of gastroenteritis,
with nausea, emesis, anorexia
and in young infants especially,
premature, young infants,
neonatal necrotizing enterocolitis.
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.
Of those 10% experienced a fatality.
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.
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.
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.
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.
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.
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.
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.
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.
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.
80% of patients with infection
by SARS-Coronavirus II,
have complete resolution and
in fact many are asymptomatic,
15% develop severe infection
5% develop critical infection,
typically requiring respiratory support of some,
either non-mechanical or non-invasive ventilation
or invasive ventilation.
1.2% is the
mortality rate, although this does vary.
typically depending on the age demographic,
those countries with older populations,
have a higher rate or higher
risk of higher case fatalities.
Clinical manifestations, as noted,
many of these patients with
SARS-Coronavirus II infection or COVID-19,
are asymptomatic or mildly symptomatic.
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.
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.