H5N1
Influenza A virus sub-groups are identified by two specific
types of surface proteins that are required for it to infect
a cell (Hemmagglutinin) and to exit the cell after reproduction
(Neuraminidase). H5 is the Hemmagglutinin designation given
to a sub-group of Influenza A viruses that have shown a particular,
but limited, ability to infect humans, sometimes with serious
consequences. Strains of two other sub-groups, H7 and H9,
have also infected people in a limited way but without serious
implications.
H5N1 is
not a single virus but really a sub-sub-group of very similar
viruses that have all proven lethal to bird life, killing
within a few days. Recent studies have already identified
two distinct H5N1 viruses that have infected people. Its infection
of humans however is limited to those who have very close
contact with infected birds or have close prolonged contact
with an infected person. Yes, as reports have suggested, it
almost certainly can be transmitted between people but not
very easily.
The reason
for this is that it is still a pure Avian virus normally infecting
the intestinal tracts of birds via faeces or, in the case
of Raptors, by eating infected birds. When infecting people,
by contact, it can only lodge in deep lung tissue and not
in the nasal passages or upper air tracts. This makes it difficult
to catch and very difficult to transmit to someone else. No
coughs and sneezes passing it around. The deep nature of the
infection is also one of the reasons why it has been difficult
to treat.
Other
mammals that have become infected include, domestic/feral
cats, big cats, ferrets, pigs, civets and a dog. Some were
confirmed as eating infected dead birds and it is likely the
remainder caught it the same way.
The worry
now is that this virus may mutate into a form that can infect
upper respiratory regions and become a very infectious human
disease.
Mutation
Mechanisms
Mutations generally take two forms. The first are mutations
that are natural incremental changes which occur in Gene sequences
as the virus reproduces and is affected by the same kind of
evolutionary selection criteria as other life forms. Given
time these eventually produce viruses with different characteristics
and capabilities. For example - the ability to infect a different
species, a change in infection pattern & symptoms, an
increase or decrease in the seriousness of infections and
developing resistance to medication.
The other
mutation form is the “Mixing” type, applicable
to most Human Influenza viruses. This is where different viruses
swap or share segments of DNA. The mixing of DNA segments
occurs when a single animal/human is infected by two different
viruses at the same time, Genes can get exchanged, producing
totally new viruses (or strains). With respect to Influenza,
popular theory placed the Pig firmly at the centre of this
event as the ‘Mixing Chamber’, because it can
become infected with both Avian and Human Flu, and just happens
to live in close proximity to Birds & People in the Far
East.
The pig
appears to have been removed from the H5N1 equation but the
fear is that, if sufficient people become infected, some may
also be infected with a normal human seasonal flu strain and
the prospect of gene mixing becomes stronger. This type of
mutation is a real wildcard as a fairly harmless variant could
be produced just easily as a very dangerous one.
A couple
of interesting aspects emerge as this field is studied more
closely. The Lethal factor of H5N1 seems to follow a similar
pattern to the 1918 Influenza epidemic, in that it hits the
healthiest young adults particularly hard, unlike normal influenza
which causes most fatalities amongst the very young, old and
infirm. Although still not confirmed, this infection pattern
seems to be the result of an excessively robust response by
the body’s immune system, causing severe tissue inflammation
and producing excess fluids in the lungs. In other words,
the healthier the individual, the more extreme the reaction
to infection.
The question
is – “What changes in infection patterns can we
expect after mutation into a fully human infective form?”.
Currently H5N1 infects only the deep lung tissue, which when
coupled with the extreme immune response of healthy people,
results in the current 50% plus fatality rate. Should the
mutation increase its human infection capability by enabling
it to infect the upper respiratory tract - Will this also
reduce or eliminate the deep lung infection capability and
will it still have the ability to over-inflame the body’s
defences?.
Of course,
this feared mutation may never occur but experts suggest anywhere
between a 15% to 50% chance. The reality is that it may not
happen this time but a similarly serious viral pandemic will
certainly occur one day. To our advantage, the current H5N1
worries have spurred a tremendous amount of research and investment
into understanding how viruses work and we are rapidly gaining
the tools to fight more efficiently in the future. The big
fear is that, should a lethal human infective form emerge
within the next year, will not be ready.
Antibodies
- Keeping pace with mutating viruses
Antibodies
are those elements within the body that fight diseases. Without
going into too much detail, the body’s defence systems
have to identify each New infection, before it can start produce
sufficient quantities of antibodies to kill the invading organisms.
If it cannot do this job quickly enough the infection can
kill the host before it is defeated. After the infection is
eliminated, the body retains this Identity Information so
that any subsequent infection by the same disease is quickly
spotted and destroyed before it takes hold.
Vaccinations
are a means of introducing either dead or deactivated diseases
into the body so that the Identity Information for that specific
disease is created and in place ready for the real thing.
It means that when a genuine infection occurs, it is quickly
eliminated naturally by the body with little or no symptoms.
The problem occurs when rapidly mutating diseases like Influenza
A come along, the body's defences only have old identity information
and it does not recognise this new invader until too late
to prevent full blown symptoms. This is why Seasonal Flu vaccines
change each year. They are re-engineered annually to accommodate
the most prevalent Influenza viruses that year.
These
New vaccines have to be developed and manufactured from each
specific Influenza strain and usually takes three to six months.
The current problem is that full scale production of a vaccine
from the current strain of H5N1 may prove useless if it later
mutates into a fully human infective form. The vaccinated
person's body might not be able to recognise it because it
has changed.
There
are several new strategies being applied to address this issue
and these will be discussed in more depth in further reports.
Report
dated 25/3/2006 - (Updated 26/3/2006) -
Copyright © Mike Elliott 25th March
2006
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