These viruses like influenza have managed also to infect a very large number
of different animals.
And in animals they have emerged thousands of years ago and
then progress of the infected from type of animal, and
at the end, only four of them have managed to be adapted to human.
Again, an example of the importance of what we call the barrier of species.
So these two types of virus, influenza and corona viruses have similarities.
That cause sporadic outbreaks with a very high mortality.
They have a very large reservoir of different genotype.
And very importantly also they are transmitted by the airborne route,
which is the easiest way to cause an outbreak or
to be transmitted from one human to another.
Let's stop as I told you a little bit on the biological events
that could lead to human adaptation of these viruses and
let's stop on RNA which is the nucleic acid contents of these viruses.
And basically the genes that are part of
what will help these viruses to evolve toward human viruses.
When the virus replicate its genetic material, particularly antiviruses,
they use a viral enzyme that is quartered by the virus itself and
in the position to human cells, these enzymes are doing a lot of mistakes.
This leads to very frequent mutations.
And at the end of the day, after several cycles of replications,
you end up with verses that are previously very different of the verses
that was the first one in the different cycles of replication.
We have accumulation of mutations in what we call a progressive genetic drift.
Of course this genetic drift could also be associated with some
kinda pheno type that could lead to more variant strengths, or
strengths that are more adapted to humans, or more transmissible.
Another way to modify its genetic contents for corona viruses is to exchange genes.
There are several phenomenon that could help to exchange genes.
We will just focus on the one that is specific for influenza viruses.
Influenza viruses are made of different segmented genes,
when two viruses infect one cell, they can easily exchange genes.
This could lead to very important genetic change and what we call the genetic shift.