00:01
So, the subject of this lecture are two other
infectious diseases that affect the lungs
which are of great importance. One is Influenza
A and the other is Tuberculosis. So, discussing
Influenza A in more detail- The importance
of this disease is that it causes every year
winter epidemics. In most people who have not
got pre-existing disease or are relatively
young it will be the cause of bronchitis often
with marked systemic symptoms and cause what
we call flu, and the patient maybe is off
work for a couple of days but then recover.
00:32
However, these winter epidemics also can cause
exacerbations of chronic lung and cardiac
disease in patients who have those problems,
and that’s a very important cause of morbidity
and mortality. In addition, Influenza A occasionally
causes pandemics. The most famous being the
one that occurred after World War I, which
was estimated to have killed 20 million people.
00:55
And the most recent one was the swine flu
pandemic a few years ago. Influenza A is not
just infection of humans, it also infects
animals such as pigs and is very prevalent
in birds; geese, duck and chickens for example.
It’s an RNA virus, it’s coded in the surface
membrane, and in that surface membrane are
embedded two proteins: haemagglutinin and
neuraminidase. Those are important because
the structure of those proteins defines the
type of virus you have, and there are only
three main structural types, which affect
humans, that is H1N1, H1N2, H3N2. And most
of the influenza that affects humans are some
variations on those three types. As I mentioned
the human types cause winter epidemics and
occasional pandemics. In addition to the non-human
types of influenza A virus, you occasionally
get infected with avian influenza. Now these
are viral types that affect birds, but can
spread from those birds to infect a human
and they cause quite an aggressive disease.
02:00
And you’ve probably heard about avian influenza
through the news because there is a lot of
discussion about this as a cause of severe
viral infections. Fortunately, this is a sporadic
infection and does not spread from the infected
person to another infected person, as yet.
02:16
And the most famous example is H5N1. So what are
the clinical manifestations of the influenza
virus? Well these are created by the fact
that it’s a virus that infects and kills
respiratory epithelial cells. If somebody
is infected with Influenza A, they will cough
out virus particles. Those are inhaled by
the next person to get infected and then they
will invade the epithelial cells, replicate
within the epithelial cells, and then eventually
kill the epithelial cells, releasing the viruses
to infect more epithelial cells in the same
person, and also to be coughed back out into
the environment to cause infection. And because
of this ability to transmit between people
readily, that is why the virus causes epidemics
and pandemics. The actual infection of
the respiratory epithelium
itself causes several distinct clinical problems-
firstly, as I've mentioned already it causes
a bronchitis, cough, phlegm production,
some systemic symptoms, with feeling ill and
fever, but not an infection deep in the lungs,
just in the tracheal bronchial tree, and with
that you may get a sore throat and the upper
respiratory tract symptoms of a runny nose,
etc. Occasionally the virus also causes gastroenteritis
symptoms because it infects the gastrointestinal
system and very rarely it can spread to
cause encephalitis.
03:36
Within the lung, there are three main problems,
which cause deaths. One is that the infection
with the virus unfortunately weakens the immune
system against bacteria, and that means that
Influenza A infection will allow a bacteria
to get into the lungs and cause a secondary
bacteria pneumonia and that is the main method
by which the pandemics have caused death in
the past. In addition, the virus itself
can spread to
affect the alveoli and cause what we call a
primary viral pneumonia, and these are generally
speaking very aggressive and they are associated
with a high mortality, but they are relatively
rare. The normal winter epidemics, unfortunately
if they affect somebody who has got chronic
heart, lung or kidney disease will cause the
underlying disease to deteriorate, to get
worse. So Influenza A is a common cause of
exacerbations of COPD, heart failure and renal
impairment, and that’s associated with a
higher degree of morbidity and mortality.
04:40
So what’s the management in Influenza A?
For most people, actually we just clinically
recognize they have Influenza A they take
a couple of days off work they get better.
04:50
If you need to, if the patient is badly affected,
coming into a hospital for example, then you’d
like to confirm the presence of influenza
A, and that can be done by nasopharyngeal
swab which can be tested using immunofluorescence,
antibodies against influenza A’s antigens,
or the polymerase chain reaction to try to
amplify the presence of the Influenza A DNA,
and that will identify patients who have active
infection, and it is a very good test. But if
it’s only really necessary in the high risk
patients or they will be hospitalized.
05:21
If you have somebody with Influenza A and
you want to treat them, the neuraminidase
inhibitors which target that surface protein,
the neuraminidase will help the patient recover
from infection more quickly than if they were
not given the treatments itself. It also probably
reduces the chance of the infection being
transmitted to other people. Because of this
risk of superadded bacterial infection of
the lung, some patients will need antibiotics
if there is a suspicion, they may be developing
a bacterial pneumonia. A very important point
about Influenza A is that its highly contagious,
and if somebody is in hospital for influenza
A, they need to be isolated so they do not
spread the disease to other people, and because
of this ability of the viral infection to upset
the body’s physiology and cause exacerbations
of underlying disease, it’s very dangerous
if Influenza A is allowed to spread to other
people within the hospital. Lastly, and probably
most critically is that Influenza A is a disease
that can be prevented by vaccination in general.
And every year patients who are at risk of
disease or severe disease, the elderly and
those of underlying chronic disease such as
COPD or heart failure should be vaccinated
to prevent them from getting that year's version
of influenza A.