The SARS Coronavirus II, the
cause of the infection we know of,
as COVID-19, typically is
transmitted via two routes.
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.
Far less common, will be, fecal-oral transmission,
this may be due to large respiratory droplets.
Which are ingested and then excreted
via faeces or even aerosolized faeces
and potentially certainly through saliva.
Highly unlikely, but yet rarely documented,
is vertical transmission so
from mother to new-born child.
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.
Very unlikely but still unfortunately possible,
is transmission via contaminated surfaces.
And this again, has to do with
those large respiratory droplets,
which take longer to dry out.
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.
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.
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.
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.
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.
As well, asymptomatic and
symptomatic patients all transmit
the same high viral loads
for the same length of time.
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.
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.
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.
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.
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.