All
about H5N1 Avian or Bird Flu
Is this an upcoming pandemic threatening us
all?
|

Flu virus under an electron microscope, magnified 100,000
times |
Influenza is the name
given to a family of viruses with generally similar
properties. These
viruses mutate and it seems each year has a slightly
different strain of virus traveling around the world.
In the past there have been occasional pandemics of
influenza, the most notable of which was the Spanish Flu in
1918-19. Some
people believe there is a grave danger of a new pandemic in
the near future. Here's why.
Part 1 of a 3 part series -
part 2 discusses strategies to
minimize your risk of infection and what to do if you should
come down with Bird or Swine Flu. Part 3 will discuss the social
problems that may occur during any type of Flu pandemic and
offers some suggestions about how to survive in a
potentially hostile, foodless and lawless world. |
Influenza is commonly confused
with the common cold. Although both are viral in origin,
and both may share some symptoms (eg a cough), real influenza is
a much more severe affliction that people regularly die from.
Different types of flu vary in
terms of how easily they can be passed from one infected person
to another person, and in terms of how severe an illness they
cause. It is happily rare to find a strain of flu that is
both highly infectious and also very lethal.
But on occasion, this can and
does occur. There is a danger that the world may be about
to confront another one of these 'super-flu' outbreaks, based on
what is currently termed avian flu or bird flu, and
scientifically described as the H5N1 flu.
Important
Disclaimer
I have no
medical qualifications and this article is not
intended as medical advice. Although I've had
physicians check the article for gross errors and
inaccuracies, they too would not want you solely
relying on this article, and we all urge you to
check with your personal health care provider and
prepare a strategy best suited for your situation. |
Lessons from the Past - the
1918-19 Spanish Flu Pandemic
Most people remember reading
about the Black Death - the plague - in the Middle Ages.
This was a horrifying pandemic (see below
for definitions), all across Europe, with many people dying.
But, at the same time, we relegate our knowledge of that to a
'could never happen to us in today's society' category.
Probably this is true.
Surprisingly, though,
there's a much more relevant example of a pandemic, and one with
clear lessons for us today. This example is less appreciated - the outbreak of influenza in 1918 that grew to
become the worst pandemic in world history. More people
died in a single year than died in the four years of the plague
between 1347-1351; and twice as many people died in six months
than died in all of the four years of World War 1.
Exact numbers for this
pandemic are hard to establish, and different sources offer
different numbers, but in the same general range.
Estimates suggest that between 20% and 50% of the entire world's
population was infected, and as many as 50 million people died.
Surprisingly, people in the 15-40 age group - normally the
segment of the population most resistant to infections - were
seemingly the most at risk.
The death rate in the US was
approximately 2.5%, compared to a 'normal' year's flu which was
about 0.1%. In other countries the death rate ranged up as
high as 5%.
The flu would attack
quickly, with people transitioning from apparently healthy to
dead in less than a day. 25% of the US population was
infected, even President Woodrow Wilson caught the flu.
Initially, governments were
slow to acknowledge this outbreak and the danger it posed, and
preferred to refer to the pandemic as 'only the flu' so as to
prevent panic. But as the world fell into the grip of what
became termed the 'Spanish Flu', social disruptions became
increasingly extreme. Restrictions were placed on public
gatherings (including funerals and even store sales) and on
travel. In San Francisco and San Diego it became
compulsory to wear gauze masks in public, and one town made
shaking hands illegal.
Desperate shortages of
health care professionals existed, and similar shortages
affected other service industries - in some cities, there were
not enough phone operators to allow for normal phone service.
There were also shortages of coffins, morticians and
grave-diggers, such that mass graves were dug by steam shovel
and dead bodies buried en masse.
To put the impact of this
flu outbreak in another context, 25 million people have died of
AIDS in the first 25 years of this disease. In comparison,
25 million people died of flu (in a world with a much smaller
population) in 25 weeks.
The Spanish Flu outbreak
occurred 87 years ago. What is the relevance of Spanish
Flu then to Bird Flu now?
Not only does the Spanish
Flu outbreak give us a taste for what could occur with a new
outbreak of a virulent strain of influenza, but recent research
now suggests that the Spanish Flu virus was initially a bird flu
virus of type H1N1 which mutated and became capable of attacking
and being transmitted between humans - exactly as is feared for
Bird Flu.
The Potential Dangers with
Avian/Bird Flu
An
unprecedented epizootic avian influenza A (H5N1) virus that
is highly pathogenic has crossed the species barrier in Asia
to cause many human fatalities and poses an increasing
pandemic threat.
The reality of the dangers
of Avian Flu is changing daily - and getting worse with each
passing day. These words, above, open a 29 Sept 2005
scholarly article in the
New England Journal of Medicine, and represent perhaps the
most recent version of the truth and also one of the most
apocalyptic.
At present the H5N1 strain
of influenza, commonly called Avian Flu or Bird Flu has been
thought to be primarily
a threat to bird populations.
It was first uncovered in
poultry in Hong Kong back in 1997, but is not restricted only to
poultry. It seems to freely attack most types of birds,
including long-range migratory birds. Its presence in wild
migratory birds makes it easily passed around the world, and
indeed it has been moving out from its original base in Hong
Kong and now is in much of Asia and moving into Eastern Europe
(primarily in Russia, almost to the Ural Mountains).
The impact of this disease
on bird populations is unfortunate, but in and of itself, is
little reason to provoke alarm in humans. But there are
some reasons to be concerned.
Firstly, the disease seems
able to be weakly transmitted from birds to people. Some -
but not many - people who are in regular close contact with
poultry have been affected by the disease as well, and
apparently some visitors to a zoo in Indonesia were also
infected, although it is unclear if this infection was from
birds or from perhaps another person.
Secondly, when a person is
infected by H5N1 flu, the mortality rate - chance of them dying
- is extremely high. It is hard to be
specific at this early stage, but estimates of mortality rates
are ranging up above 50% (as of 5 August 2005, there were 112
cases and 57 deaths, outside of China. Total deaths have
now (late Sept) increased to 65, but a matching number of total
cases is not available.) In contrast,
'only' 2.5% - 5% of people infected with Spanish Flu died.
Remember this number.
H5N1 is currently proving to be at least ten times more
lethal than Spanish Flu.
On the other hand, these
early statistics, like first returns from an election, can be
misleading. It is quite possible that not all cases of
H5N1 infection (where the person survives) has been accurately
tracked, and of course, the infections to date have been in
third world countries with generally poor standards of nutrition
and healthcare. Actual mortality rates may be much
lower than presently indicated.
Thirdly, although at present
the disease has not yet been proven to be transmittable from one person to another,
this may change. There are a couple of ways this could
occur - a random mutation in the virus could do this, or the
H5N1 virus could be passed to a person infected with a 'regular'
(ie person to person type) flu virus; the two flu viruses could
exchange genes, causing a new strain of the H5N1 to become
transmittable between people.
If this occurs, a
devastating global pandemic becomes possible.
How Likely is it the Virus will
Evolve to Human to Human Infection
Bird Flu was first
discovered in 1997. Why are we worrying about it now,
eight years later? Surely, if there was a clear and
present danger, it would have already manifested itself?
Some people have asked these
questions as a way of suggesting concerns about Bird Flu are
being overstated. But the Bird Flu problem is contained
within these two questioning statements. Firstly, Bird Flu
has shown itself to be difficult to contain and/or eliminate.
Bird Flu has become more widespread with the passing of time; it
is getting more widely distributed and infecting more and more
bird populations, in more and more countries, every week.
The very small risk factor associated with Bird Flu in 1997 has
been steadily growing ever since.
Secondly, the chances of the
H5N1 Bird/Avian Flu virus evolving into something dangerous to
humans increases based on two things - the prevalence of Bird
Flu, and the length of time it has been in existence. The
more time the virus has, the greater the chance that a random
change in its makeup will make it more dangerous to humans.
Accepting then that Bird
Flu's eight year life to date is not a reason for complacency
but rather a reason for concern, we should consider two issues.
Firstly, will such an evolution occur, and secondly, how
infectious will the resulting virus be?
The Virus is already evolving
The answer to the first
question might be unexpected. There are already (as of
September 05) between four and six known cases of human to human
transmission of the H5N1 virus. See, for example,
this report.
And
this article contains alarming data that suggests human to
human transmission is already occurring in Indonesia.
This article, two days later, adds to the concern.
Still not convinced?
This page from the CDC website and headed 'Outbreak Notice:
Human Avian influenza, Asia' will probably change on a regular
basis, but on 27 Sep 2005 included the text 'A
few cases of person-to-person spread of H5N1 viruses may have
occurred.'
Note the first of these
articles refers to the disease moving to a 'phase five'.
This is one step short of phase six which is a fully fledged
world pandemic. The WHO, (World Health Organization, and author of these six levels of
alert (detailed below)), is currently treating
Avian Flu only as a phase three alert.
Some people have said there
is no direct evidence the virus is about to mutate into a human
to human transmittable form. That claim may already be
negated by the information above, but even if still true, the
statement is meaningless - it is a bit like saying 'there is no
direct evidence the next time you roll the dice it will come up
with a six'.
The likelihood of mutation
increases over time, and as more and more people are exposed to
infected birds. The virus might never mutate into a robust
human to human transmittable form, and most mutations lead to a
weaker rather than stronger organism. But, on the other
hand, it might. And, in particular, if the H5N1 virus
invades a person already carrying a human to human version of
the flu, the chance of the two viruses exchanging DNA and
acquiring attributes of each other increases.
How infectious would such a
mutated virus be? Nobody yet knows. Maybe it will be
a very weak virus that is hard to pass on to other people.
Or maybe it will be a super infectious virus, long lived, hard
to destroy, and dangerous in very small quantities.
There are many unknowns
here. But the extraordinary danger that accompanies the
risk of realistic scenarios is surely more than sufficient to
motivate us and our governments to do all we can to stop this
from happening.
The Government (or Science)
Will Save Us?
I spoke about Bird Flu with
my general practitioner, and he agreed about the grave dangers
posed by Bird Flu. But he concluded by saying he
believed/hoped that technology would triumph, and by the time
the virus became a major problem, there'd be a vaccination or
cure for it.
How realistic is this hope?
Alas, not very, although a lot depends on the timeline of when
(if) the virus starts actively passing from person to person,
and if a vaccine is developed and distributed prior to this
occurring.
Flu Vaccine
As of the time of writing
(Sept 05) there is no vaccine effective against the H5N1 strain
of Avian Flu. There are a couple of vaccines under
development, but it is unclear if they will pass all testing,
and - if/when they do - how long it would take for them to enter
mass production, and how much longer it would then take for a
realistic number of doses to be made available to the general
population (approximately 6.5 billion).
The
vaccines under development are expected to enter trials
variously later this year or next year.
Probably it will be more
than six months after a suitable virus has been developed before
limited quantities of vaccine become available, and
substantially longer than that before sufficient (how much is
sufficient when we're talking about a world-wide pandemic?)
quantities are made.
To quote from a
page on the WHO website (link no longer active)
Current global manufacturing capacity (estimated at 300
million doses of regular trivalent influenza vaccine per
year) is inadequate to meet the expected global needs during
a pandemic and cannot be rapidly augmented.
Flu Drugs
There are two main families
of drugs used to fight an infection once a person has been
diagnosed with H5N1 flu. The first of these types of drugs
- M2 inhibitors such as amantadine and rimantadine - have been
widely in use for some years. Unfortunately,
indiscriminate and uncontrolled dosing of poultry with these
drugs in China means, as of the time of writing (Sept 05), most
strains of the H5N1 virus have developed resistance to these
drugs.
The other family of drugs -
neuraminidase inhibitors such as zanamivir and oseltamivir (Tamiflu)
- are more expensive and have not been so widely used to date.
While it seems the virus has not yet developed any effective
resistance to these drugs, with the passing of time and their
continued use, the second family of medicines must be considered
vulnerable to the virus developing resistance too.
Unfortunately, Tamiflu is in
short supply, and most countries and their public health
authorities have insufficient stocks in case of a pandemic.
Update 2009 :
Tamiflu is nowadays much less effective, due to the flu virus
mutating in response to Tamiflu to become resistant.
Preparing for an Outbreak
If an outbreak of H5N1 Avian
Flu were to occur, the best response would be to urgently give
infected people courses of the anti-viral Tamiflu drug, and
possibly also to give extra courses of Tamiflu to people in
close contact with the infected person.
Each course of Tamiflu for
one person comprises ten 75mg tablets. Taking Tamiflu as a
preventative measure rather than as a cure can require even
larger numbers of tablets, depending on the length of time the
protection is desired (you are only protected against the flu
while actively taking the tablets - there is no lasting effect).
But if an outbreak were to
occur and spread with anything like the speed of the Spanish Flu
in 1918 (25 million dying within the first half year) the world
would need access to huge amounts of Tamiflu. We'd be
reliant on public health authorities having stockpiles of the
drug.
Although governments are
slowly recognizing the danger and ordering supplies of Tamiflu,
no government is ordering sufficient amounts for their entire
population, and very few are ordering enough for even one third
the population. The UK has stockpiled 15 million courses,
enough for one quarter of their population. France also
has enough for one quarter of its population. Australia
has 4 million doses, sufficient for 20%. But the US?
We have only enough Tamiflu stockpiled for 1% of our population.
Even those countries that
are ordering large quantities have priority lists of who will
get access to them. If you're not a politician, health
care worker, or other key services employee, your chances of
getting access to these stockpiles is very limited.
Based on current and
projected near-term future order fulfillments, a widespread
outbreak of Bird Flu could very quickly lead to all supplies of
Tamiflu being exhausted. Indeed, my local pharmacy on 28
Sept was out of stock, although they expect more in soon.
All of the above assumes
the virus doesn't gain resistance to Tamiflu. And this
may already be occurring, as this article, dated back in
May, suggests. (Update 2009 - yes, Tamiflu's
effectiveness is now massively reduced, and there's no new drug
to replace Tamiflu).
Preventing Spread of Infection
among People
The SARS danger was
circumvented largely by effective controls on the movement of
potentially infected individuals.
But if Bird Flu is to be
transmitted both by people and by animals (obviously birds, and
potentially cats and possibly pigs, too) then while we can
realistically limit the movement of people, we almost certainly
can't prevent the movement of wild birds.
Preventing Spread of Infection
among Birds
Bird populations with the
remotest likelihood of infected members need to be completely
eradicated. Some nations have been willing to do this.
Others have been less willing to suffer the economic damage
they'd be inflicting on themselves.
Unfortunately, many of the
South East Asian nations with Bird Flu infections are poor
countries with low standards of health care, low standards of
education, and high levels of corruption. The temptation
for officials to accept bribes and to allow bird flocks to
remain unharmed must be great and at times overwhelming.
And while these nations
might seem impossibly far away and removed from our way of life
here, the reality is that many of them are no more than one or two flights away. A person can be infected in South
East Asia, and less than 24 hours later, he can be walking the
streets and riding the subways in New York, coughing into the
air around him, and spreading the infection. One of those
people riding alongside him in the subway can then fly to
somewhere else, and so the chain of infection rapidly spreads
like wildfire.
While this article primarily
considers the implications of Bird Flu becoming a risk to
humans, the economic damage that 'simple' Bird Flu can cause is
also major. Poultry is a major meat source in this and
many other countries, and if there became a need for major
culling of commercial poultry farms, not only would there be a
direct cost to the affected farmers, but the resulting shortage
of poultry would raise prices of all meat and poultry related
products.
Controlling an outbreak in
birds is proving to be difficult (this strain of Bird Flu has
been around for eight years already). Indeed, the current
Bird Flu problem (in birds) is getting worse, not better.
Since mid-December 2003, a growing number of Asian countries
have reported outbreaks of highly pathogenic avian influenza in
chickens and ducks. Infections in several species of wild birds
and in pigs have also been reported.
This following quote comes
directly from the
WHO website (link no longer present)
The rapid spread of highly pathogenic avian influenza, with
outbreaks occurring at the same time in several countries, is
historically unprecedented and of great concern for human health
as well as for agriculture.
Is the Danger of H5N1 Flu being
Deliberately Understated or Ignored?
It is probably not in the
general interest of public order and contentment to unduly alarm
or panic people over something that might never occur, and it
seems likely that governments are seizing on this rationale as a
reason to avoid dramatic public discussion of this problem.
Furthermore, an outbreak of
a virulent strain of human H5N1 would be so apocalyptic and
exceed anything in any of our memories or comprehension, so
there is an automatic instinctive unwillingness to believe or
accept the grim reality of what would occur, coupled with a
desperate desire to hope that such terrible things may never
come to pass.
But wishing something were
not true does not change it, any more than an ostrich with its
head in the sand becomes truly invisible. The inexorable
spread of an infectious disease makes no allowance for the
social destruction it might be causing.
Modern society, rather than
making a pandemic less likely, has all the factors to make such
an occurrence more likely : crowded living, working, and
commuting conditions in many cities encourage and facilitate the
spread of the disease, and large numbers of people traveling all
around the world every day ensure the disease can spread not
only within each minor community cluster, but between clusters
and between countries, too.
Our society has a curious
duality about acceptance of risk. Some things with high
risks we complacently accept without a second thought.
Smoking cigarettes, driving a car (drunk or sober!), unprotected
sex with strangers; many things with high risk of serious
consequence are accepted without any qualms. But other
situations with vastly lower risks attached - for example,
living in a house with lead based paints or asbestos in the
ceiling, or flying in planes - are considered very risky and
surrounded with many controls and restrictions.
Our perception and
acceptance of risk is irrational; but the threat posed by a Bird
Flu pandemic demands a rational analysis and response.
Hurricane Katrina gives a
good example of something that was considered to be so unlikely
as to be not worth giving full attention to. The result
was $200+ billion dollars worth of rebuilding, hundreds of
people dead, and hundreds of thousands more with lives
transformed to misery.
A human to human infectious
H5N1 virus is not a certainty. But it is a possibility,
and the chances of it occurring are probably similar to or
greater than the chance of another Katrina hitting New Orleans.
The devastation caused by a human Avian Flu virus, not just in
one small area, but to the entire country and entire world, is
unthinkably larger than any natural disaster, whether measured
in lives lost, the dollar cost of the pandemic and recovery from
it, or any other parameter.
For the sake of ourselves
and our families, we must consider this risk seriously and
respond accordingly.
While some publicity is
supporting this view, there is also a confusing and
contradictory counter-current of 'relax, don't worry' type
stories being published.
Here's a
curious article which seeks to reassure us. But
unfortunately it contains some factual errors and some
significant omissions.
For example, Bird Flu isn't restricted
only to poultry - populations of migratory birds have also been
infected, and are rapidly spreading the disease away from its
initial location (Hong Kong).
And this quote 'Numerous
health professionals are monitoring influenza; and, training,
surveillance and education efforts continue. Plans for dealing
with an influenza emergency have been developed and are
continually updated so that the best control efforts available
could be implemented should the need arise' sounds very
reassuring, but is not backed up
with the specifics of who these health professionals are, or
what their plans are. Anyone who relied on the government
to save them from Hurricane Katrina will probably find these
words less than reassuring.
Furthermore, the
elapsed time between the onset of an outbreak and a fully
fledged pandemic may be very short, giving little or no time for
public health officials to adequately respond, be they prepared
or not.
While populist articles seem
to often downplay the risk, medical journals tell a
different story. Indeed, Dr Julie Gerberding, head of the
CDC - the Centers for Disease Control and Prevention; the US
organization that would presumably be a first responder and coordinator of a flu crisis in the US,
was quoted as saying (link broken) on 21 Feb 2005
Bird flu is the single
biggest threat to the world right now and health officials may
not yet have the tools they need to fight it.
In a report to the American
Association for the Advancement of Science, she added 'this is a
very ominous situation for the globe' calling it the 'most
important threat we are facing right now.'
Here's another
article, quoting from Northern Ireland's Department of
Agriculture and Rural Development, claiming the risk of
dangerous avian influenza reaching Western Europe is low.
This claim would seem to be largely contradicted by the facts
they admit themselves - avian flu has already reached Russia.
But this
article, linked from the same page, refers to other western
nations as being fearful of the spread of the flu, and closes with a chilling quote from the Secretary
General of the European Public Health Alliance, which represents
115 European health groups. She says :
Millions and millions would die, and a pandemic would change
society as we know it. And no-one seems prepared.
On the other hand, the
article also quotes a WHO spokesman as predicting that between
two and seven million people could die, world-wide, if a
pandemic (which he describes as 'inevitable'!) should break out.
This number seems comically
(or is that, tragically?) low. Somewhere up to 100 million
people died from Spanish flu, a virus that killed 2.5% - 5% of
the people it infected, in a world with only 1.8 billion people.
Today we have a world with 6.5 billion people and a virus that
kills half of the people it infects.
What is the US Government
Doing?
Here is a
fascinating transcript (link no longer works) of a recent interview between Bill
Moyers and Dr Anthony Fauci, director of the Institute for
Allergy and Infectious Diseases at the National Institutes of
Health on the PBS Wideangle show.
Some reassurance may perhaps
be gleaned from this part of the interview :
BILL MOYERS: Ready. You know, we were not prepared for 9/11.
We were not prepared for the ravages of Katrina. What makes
you think we're going to prepare for this?
DR. ANTHONY FAUCI: Because we're on our way to doing that.
There's a commitment that certainly the administration --
the President is committed to getting us prepared for a
pandemic flu.
He's following it very carefully.
Secretary Leavitt of the Department of Health and Human
Services, [it] is of highest priority for him in his
department.
So
this is something that at the very highest levels of our
government from the White House to the Departments to the
Congress are very concerned about this.
Unfortunately, Dr Fauci's
comments seem contradicted by Senator Frist's comments,
below.
Summary
There have been previous flu
pandemic scares that have come to nothing. It is possible
that the potential danger of Bird Flu too will prove to be
overstated - and let's all fervently hope this proves to be the
situation.
But, wishful thinking to one
side, the grim reality at present is that the persistence,
growth and spread of Bird Flu virus in bird populations steadily
increases the possibility that the virus not only may but can
and will evolve into a form more compatible with human to human
transmission.
If this happens, and if the
virus remains as lethal to humans as it currently appears to be,
the result could be horrifying. Bird Flu is ten to twenty
times more deadly to humans than was Spanish Flu in 1918-1919.
Without adequate prevention and controls, as much as 10% of the
entire world's population - rich and poor, west and east - could
die from a Bird Flu pandemic. It is probable that such an
event would destroy much of our present civilization and society
for an extended period of time.
At present there is little
reassuring evidence that adequate prevention and control
measures are in place. Forget about worrying if an
asteroid might hit the planet, don't worry about global warming,
and ignore the energy crisis. Although a Bird Flu pandemic
is far from certain, if it were to occur, the immediate disaster
to all of us would eclipse any of these other future problems.
Accordingly, everyone's
highest priority must be to resolve the clearest and most
present danger to life as we know it - Bird Flu.
We'll
give the last word to surgeon and politician Bill Frist, who
starts off
a must read piece in the Washington Times on 29 Sept by
criticizing his own government's administration by saying :
The avian flu virus is a pathogen invisible to the human eye
which poses an immense potential threat to American
civilization. In the past several months, it has become
clear to me that we remain dangerously unprepared to defend
ourselves against it....
Read more in Parts 2 and 3
In
Part 2 we discuss strategies to minimize your risk of infection
and what to do if you should come down with Bird or Swine Flu. Part
3 will discuss the social problems that may occur during any
type of Flu
pandemic and offers some suggestions about how to survive in a
potentially hostile, foodless and lawless world.
Reference Resources
This subject is rapidly
evolving and the information in these two articles may quickly
become out of date. Fortunately, there are a number of
websites that are dedicated to distributing the latest
information about Avian Flu.
Centers
for Disease Control and Prevention section on Avian Flu
National Foundation for Infectious Diseases Information about
Influenza (link no longer works)
World Health Organization section on Avian Influenza
Definitions
The following terms are
often used in discussions of influenza and other diseases, and
so these definitions may be helpful.
Communicable (disease)
A communicable disease is
one which is both contagious and also which can be passed on
indirectly (as by a fomite or vector).
Contagious (disease)
A disease is said to be
contagious if it can be passed on by contact between an infected
person, or a discharge from such a person, and an uninfected
person.
Endemic
A word that sounds like
epidemic but which means something quite different. An
endemic thing is something that is generally restricted to a
specific location.
Epidemic
A thing which affects an
unusually large number of people in a region at the same time.
Fomite
A fomite is a physical
object that acts as an intermediary in the transmission of a
disease from one person to another. For example, if you
cough onto a door handle which another person then touches and
then puts his contaminated hand in his mouth, the door handle
has acted as a fomite. cf vector.
H5N1
Influenza viruses are
categorized by the subtype of two surface antigens on the virus,
a Hemagglutinin type and a Neuraminidase type. There are
at least 16 different H antigens and nine N types (with types N1
and N2 being capable of causing infections in people).
Infectious
This refers to a disease
having a broader capacity to be passed on to an uninfected
person than a contagious disease. All contagious diseases
are infectious, but not all infectious diseases are contagious.
An infectious disease is one caused by the introduction of
organisms (eg bacteria or viruses) into one's body which then
grow and multiply there.
Pandemic
Can be thought of as a more
severe epidemic in terms of the percentage people affected, and
extending over a broader region.
Vector
A vector is an animate
organism that transfers disease from one person to another
person. For example, mosquitos are the vector for malaria.
cf fomite.
The Six
Phases of a Pandemic
The World Health
Organization (WHO) has developed a global influenza preparedness
plan, which defines the stages of a pandemic, outlines WHO’s
role and makes recommendations for national measures before and
during a pandemic. The phases are :
Interpandemic period
Phase 1 : No new
influenza virus subtypes have been detected in humans. An
influenza virus subtype that has caused human infection may be
present in animals. If present in animals, the risk of human
infection or disease is considered to be low.
Phase 2 : No new
influenza virus subtypes have been detected in humans. However,
a circulating animal influenza virus subtype poses a substantial
risk of human disease.
Pandemic alert period
Phase 3 : Human
infection(s) with a new subtype, but no human-to-human spread,
or at most rare instances of spread to a close contact.
Phase 4 : Small
cluster(s) with limited human-to-human transmission but spread
is highly localized, suggesting that the virus is not well
adapted to humans.
Phase 5 : Larger
cluster(s) but human-to-human spread still localized, suggesting
that the virus is becoming increasingly better adapted to
humans, but may not yet be fully transmissible (substantial
pandemic risk).
Pandemic period
Phase 6 : Pandemic:
increased and sustained transmission in general population.
Important
Disclaimer
I have no
medical qualifications and this article is not
intended as medical advice. Although I've had
physicians check the article for gross errors and
inaccuracies, they too would not want you solely
relying on this article, and we all urge you to
check with your personal health care provider and
prepare a strategy best suited for your situation. |
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Originally published
30 Sep 2005, last update
20 Jul 2020
You may freely reproduce or distribute this article for noncommercial purposes as long as you give credit to me as original writer.
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