This course proposes an overview of current global health challenges drawing on the insights of several academic disciplines including medicine, public health, law, economics, social sciences and humanities. This interdisciplinary approach will guide the student into seven critical topics in global health.
Emerging Viruses in 2013: Influenza A H7N9 and Middle East Respiratory Syndrome-Coronavirus by Laurent Kaiser
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Del curso dictado por University of Geneva
Global Health: An Interdisciplinary Overview
154 calificaciones
De la lección
Emerging Trends in Global Health: Infectious Diseases
There are 7 parts to module 3. Lessons 3 & 4 are both introductory sections that describe key concepts necessary to understand infectious diseases and how we deal with them. Lesson 5 constitutes the core lesson of module 3. This lesson focuses on the current global situation and future challenges for the most prominent infectious diseases of the world. In lessons 6-9 we discuss neglected tropical diseases, re-emerging infectious diseases and epidemics/pandemics. Finally, lesson 10 and 10b summarize module 3 in a set of key conclusions.
Conoce a los instructores
Rafael Ruiz De CastañedaInstitute of Global Health - Faculty of Medicine
University of Geneva
Antoine FlahaultProfessor of Public Health and Director of the Institute of Global Health (Faculty of Medicine, University of Geneva) and co-Director of Centre Virchow-Villermé (Université Paris Descartes)
University of Geneva and Université Paris Descartes – Sorbonne Paris Cité
[MUSIC]
Hello everyone, welcome to the sessions.
The role of my presentation to discuss emerging virus and
I will focus on two viruses that have emerged in 2013.
First the Influenza A H7N9 and second the so
called Middle East Respiratory Syndrome Corona Virus.
The number of case that has been observed with these two viruses are very limited,
approximately 134 for the Influenza A viruses and
96 understand was the corona virus.
But whatever the mortality rate associated with infection is very high.
And this is the reason why we are very preoccupied to
follow the evolution of these viruses.
So in conclusion we have a limited number of case with high mortality rate, and
this explains why organization like WHO or
other else organizations care about these viruses.
And the main question is to identify whether this virus
could adapt to humans from its animal reservoir to cross the barrier of species.
And then to be really human adapted in order to cause a pandemic for example.
And this is what I will discuss today.
And for this, I will discuss of the animal reservoir of these viruses.
So we'll discuss of the diversity of these viruses.
And also I will stop few minutes on the genetic matter of
these viruses that are made of RNA, which is very important to understand
in term of biological aspects could lead this virus to be adapted to humans.
Let's start with influenza.
Influenza A are viruses characterized by the presence
of the surface of two glycol proteins, the hemagglutinin and neuraminidase.
The hemagglutinin we know in the nature approximately seventeen
different hemagglutinin.
And approximately ten different neuraminidines.
And we use these two liquid proteins to classify these viruses.
In humans we know only basically three
hemagglutinin that have managed together to humans and to infect humans.
And on the other sides in avian birds, or in wild birds, and also in pigs.
We can find a very high number of different and
migrating in and up to 17 and the ruminates.
So it just tells you that some viruses are not adaptable to humans and
could not cross the barrier of species.
And for the next few minutes I will stop on influenza and
also discuss a little bit of H1N1 2009.
And we won't have time to discuss about H5N1.
Concerning corona viruses,
corona viruses are part of viruses that are very, while adapted to humans.
Basically the first of the second cause of common cold, and
now the most frequent virus causing our respiratory tract infections.
Everyone has experienced infection with corona viruses.
Corona viruses as known by the names presented here,
and are really four different species that are adapted to humans.
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.
So in summary, influenza viruses and
in some way corona viruses also combine all the tricks.
They can accumulate mutations.
They can exchange genes and
have a very large animal reservoir that will favor the number of this exchange and
the number of mutations that are accumulate in this large reservoir.
Of course, this is not very important for humans but
this starts to be important only when these genetic change
leads to phenotypic change and then to several disease in humans
like it has been the case for these two viruses in 2013.
How long does it takes to these viruses to be adapted to human?
Let's just take one example which is the H1N1 in 2009.
In 2009, this virus emerge in humans and when we analyzed
the origin of the different genes that compose this viruses, we found that one
part of the genes come from a virus that has evolve in pigs for decades.
Another part of the genes is the, a mixture of different
genes coming from three different viruses that have combined in one pig and
then combined with the other part of the virus here in pink
to lead to this new H1N1 2009 virus.
But most interestingly, when we tried to
trace the origin of these genes we come back to the pandemic in 1918 and
we can trace the origin of most of these genes in 1918.
So in other words, the virus that caused the pandemic more than 100 years ago
has evolved in different animals and one day has combined to create this so
called that emerge again in humans.
And [INAUDIBLE] to small 100 years, which is very complicated to predict.
We have probably the same type of observations for influenza H7N9.
We can trace the origin of this virus in different birds, at least four
different types of birds, and this virus emerged probably in 2011 and 2012.
But we don't have a more precise history concerning the origin of this virus
since it's very difficult to trace the evolution of this virus in animals and
particularly in wild birds.
Is this H7N9 virus human adapted?
There are several arguments, biological arguments that suggest that the virus can
replicate easily in mammalian cells so it can be adapted to humans.
Genomes analysis reveals some mutations.
That's confer adaptations to human.
So this suggests freely that the virus could easily be humanized.
However on the other hand, when pigs are infected, they cannot transmit
the virus easily, and still the virus retains really a strong affinity for
the avian receptors that are found in wild birds.
But we really hear the article what we could call the yin and
the yang of the influenza virus, there in one part adapted to animals and
the other part could probably be adapted to humans also.
For the most corona viruses, we can trace that this virus
originated from a virus that we found in bats.
It's very close with viruses that have been identifies in bats.
It's not a virus that has evolved from a human virus.
So again, it's the same kinda story we have a new virus that emerge in human and
was identified in its regional reservoir here in particular bats.
We don't know at this time whether this virus could infect other animals
that are here in this picture.
This virus also emerged very recently based upon these
phylogeny diseases probably between 2009 and 2012.
The recent outbreaks that are still ongoing in
Saudi Arabia shown that seven mutations have already emerged and
that we already have some kinda genetic diversity and the virus is evolving.
So in conclusions the barrier of species is a real biological limitations for
many of these viruses, for any animal virus.
And virulence is really the optimal balance
transmissibility and pathogenicity.
If you can show that a virus is very dangerous or
a consider disease in animals.
It does not mean that it's dangerous in humans if it's not transmissible
at least at the large scale of a big house.
So transmissibility also is not easily achieved by any animal virus and
this is really the key to cause a pandemic.
RNA viruses have no brain and no strategy, but they have the ability to evolve,
thanks to high mutation rate, the ability to exchange genes like I showed you.
They have a very large animal reservoir that is called.
Day after day promote new strains.
The presence of different environmental and
complex environmental constraints have to be taken into account.
And what is very important that I tried to show you is the time frame
of these evolution is well beyond any human lifespan,
which really could complicate any productive prediction model
that can try to predict the evolution of these vessels and
of course will complicate any publican intervention.
And to illustrate this, we could have a look back in the 25 or
the last 30 years, and we can observe that even the most astute epidemiologists,
the best infectious disease specialists in biology has not
predicted West Nile Virus that has crossed over continents into the US.
The SARS outbreak in 2003, the Chickungunya more recently
that crossed the Pacific Ocean, the H1N1 of 2009.
We were expecting H5N1, and so
then we had the virus coming from the peaks in 2009.
And the most important year,
one of the most important pandemic of the 25 years, HIV.
It has also emerged from an animal reservoir across the burial of species and
caused this very dramatic outbreak in humans.
Thank you for your attention.
[MUSIC]
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