| As more and more cases of bird flu are
reported, the world faces an immediate threat of a
deadly pandemic. Pandemics (Global Disease Outbreaks)
are known to be like flash floods. They start abruptly,
spread fast and cause a lot of damage all over the
world.
A few facts that everyone should know:
What is Avian Influenza?
As the name suggests, avian influenza
refers to the infection caused by avian (bird) influenza
(flu) viruses. These viruses are commonly found in
intestines of wild birds and these birds can carry the
viruses without getting sick. However the viruses can be
pathogenic to domesticated birds like chickens, ducks
and turkeys. Domesticated birds become infected through
exposure to other birds or through surfaces contaminated
by secretions and faeces of the infected birds.
These viruses are classified as Low
Pathogenicity and High Pathogenicity. Most strains of
Avian Influenza come under Low Pathogenicity Avian
Influenza (LPAI) Group and produce mild symptoms in the
infected birds. Common symptoms are ruffled feathers,
decreased food appetite, decreased egg production,
sneezing and coughing. Many times LPAI may go
undetected.
High Pathogenicity Avian Influenza (HPAI)
has more severe symptoms which include sudden death,
loss of energy and appetite, decreased egg production,
respiratory problems, facial oedema (swelling), poorly
formed eggs and diarrhoea. HPAI can reach a mortality
rate of nearly 100%.
What Is H5N1 strain of Bird Flu?
All flu viruses are classified as type
A, B or C depending on their structural arrangement.
Type A is responsible for lethal pandemics and is found
in both animals and humans. Type B causes local
outbreaks of flu. Type C is the most stable of the three
and infected people show only mild symptoms of flu. Type
B and C are usually found only in humans. Type B and C
are more stable than type A and are not classified
according to their subtypes.
Influenza viruses of type A are
divided into subtypes and the naming is done on the
basis of two proteins (antigens) found on their surface
- Hemagglutinin (HA) and Neuraminidase (NA). Sixteen
types of HA and nine types of NA exist. Thus a total 144
combinations are possible.
Thus H5N1 is a type A virus and gets
its name from HA 5 protein and NA 1 protein present on
its surface.
How Do Type A Viruses Cause A
Pandemic?
Type A viruses are further classified
into strains. These strains can continuously evolve into
different strains. Their ability to exchange genetic
material with other viruses and create new influenza
viruses makes them unpredictable and difficult to fight
with. Humans have to develop new immunity (antibodies)
every time new strains are created.
Viruses cannot repair genetic damage,
small changes known as "Antigen Drift", are
continuously creating new strains of viruses. However
when genetic material from Type A viruses from different
species - say a bird and a human, comes together and
merges, an entirely new strain is created. This is known
as "Antigen Shift" Humans have no immunity to
such a strain and the strain can spread rapidly causing
a Pandemic.
How Is The Virus Transmitted To
Humans From Birds?
Usually Avian Influenza viruses do not
infect humans. Migratory birds act as carriers of these
viruses and do not get affected by them. These birds
then come in contact with domesticated birds such as
chickens and turkeys and spread the infection to them.
Domesticated birds may get the virus from contact with
contaminated surfaces too. Once a virus infects
domesticated birds, it can cause severe epidemic among
the birds. Humans come in contact with infected birds or
contaminated surfaces and pick up the virus.
In the human body, this avian flu
virus then undergoes an antigenic shift, combines with
genetic material of a human strain of influenza virus
and creates an entirely new strain of virus against
which humans have little or no immunity. These genetic
reassortments may also take place is the body of a third
species (susceptible to both avian and human viruses)
like the pig, where an avian influenza A virus and human
influenza virus mix their genetic information and
produce a new virus which might be able to infect
humans.
Why is H5N1 dangerous?
The first reported cases of H5N1
infections were detected in geese in 1997 in Southern
China. A total of 18 human infections were reported and
six of them succumbed to it. The infection spread
quickly to poultry in Hong Kong. At that time a million
and half chickens were culled in Hong Kong to keep the
virus under control. The virus disappeared for a few
years, but resurfaced in 2002 in Hong Kong again. Since
then it has killed millions of birds in Asia and many
cases of human infections have been reported.
The persistence of this H5N1 strain of
virus is a great concern for humans. Although the virus
does not spread from birds to humans easily, the
severity of the infection of H5N1 in humans is
frightening. The virus has killed every second person
infected by it. These cases were reported in perfectly
healthy individuals who had no past history of
infections. However the greater concern for the world is
the POSSIBILITY THAT THE VIRUS MAY MUTATE (UNDERGO
ANTIGENIC SHIFT) AND CREATE A FORM THAT MAY SPREAD FROM
HUMAN TO HUMAN. Such a strain of virus may result in a
pandemic, killing millions of people worldwide.
Is Consumption Of Poultry Birds
Safe?
Yes, it is safe to consume THOROUGHLY
COOKED poultry products. The H5N1 virus is sensitive to
heat and gets destroyed by normal cooking temperatures
of 70- 100 degree Celsius. If meat from poultry birds
and eggs are cooked properly, the virus will be
destroyed. Just make sure that no part of the meat
remains raw or uncooked.
How Big Is The Risk Of A Pandemic
Breaking Out?
The world had to face a Bird Flu
Pandemic, thrice in the twentieth century. In 1918-1919,
"Spanish Flu" killed anywhere between 20
million to 50 million people (exact figures not known),
including half a million in the United States alone. The
"Asian flu" in 1957-58 killed 70,000 in the
United States and in 1968-1969, the "Hong Kong
flu" killed 34,000 in the USA.
Currently the risk of H5N1 strain
leading to a Pandemic is high. The virus is spreading
fast to new areas and the efforts made to curtail it
have proved inadequate.
Domestic ducks have now become a
"reservoir" for the virus. They are acting
like a carrier for the virus - their bodies carry the
virus without showing signs of any infection. Infected
ducks then release large quantities of the virus in
pathogenic form in their excretions spreading the virus
to other birds or humans. This has made detection of the
virus difficult especially in rural areas.
According to health experts, the virus
has already met the first two prerequisites for starting
a pandemic. First it has attained a form, for which
humans have no inbuilt immunity; and second, it has
proved pathogenic enough to cause serious illness and
death in humans.
The present risk of a pandemic is very
high. The only factor that has prevented a pandemic so
far is that the virus has not mutated into a form that
would allow it to transmit efficiently from one human to
another. Once such a genetic change takes place for the
virus, a pandemic will be inevitable. The first signs of
such a reassortment will be presence of the clusters of
patients with flu symptoms, closely related - both in
time and space. This would be a clear indication of
virus having the ability to transmit from
human-to-human.
Currently no vaccine has been
developed for fighting H5N1 strain. Simultaneous work is
being done in many countries for developing a vaccine,
but no success has been achieved. The exact virus that
may cause the pandemic cannot be predetermined. Thus
mass production of vaccine before the pandemic starts is
ruled out. The worldwide manufacturing capacity is
inadequate to match the sudden demand surge during a
pandemic. The best that scientists can do is to carry
out a study and determine the smallest amount of antigen
per dose that will provide sufficient protection and
thus maximise the number of vaccines produced.
What Are The Precautions Necessary
To Prevent A Pandemic?
The logical first step is to control
the disease from spreading among birds, but this seems a
difficult task now. Bird Flu has become a bird epidemic
in many parts of Asia and is spreading fast.
The Next step is to prevent the
disease from getting passed on to humans. People who
come in close contact with birds (like poultry farmers)
are advised to keep a close watch on the health of
birds, notify any sort of sickness in birds to the
health authorities and avoid direct contact with sick
birds in all cases. (Ducks have become a reservoir for
the virus and may not exhibit signs of sickness even if
they are carrying the virus.)
In case the flu becomes a pandemic,
most countries of the world will be affected. In such a
scenario, the best preventive measures would be personal
hygiene, avoiding crowded places and staying away from
raw meat and eggs.
A flu shot does not prevent bird flu,
but it can protect a person from other forms of flu and
avoid complications. Persons above 65 years of age,
children, health services workers, people with chronic
respiratory disorders, travellers to flu affected
countries and pregnant women may consult a doctor
regarding flu vaccination.
What Are The Symptoms In Humans and
Treatment Options For Bird Flu?
A person infected by bird flu may have
all symptoms of common flu like fever, persistent cough,
sore throat and body ache. Moreover, there is a high
risk of complications such as pneumonia, bronchitis, eye
and ear infections and severe breathing problems.
Presently four drugs are used to
combat influenza.
The most effective drugs known for
seasonal flu are Oseltamivir (commercial name Tamiflu)
and Zanamavir (Commercial name Relenza). Both of these
are known to reduce severity and duration of seasonal
flu, but they may prove ineffective if the virus is
allowed to stay in the body for too long. Health
professionals advise that TREATMENT OF FLU WITH THESE
DRUGS SHOULD START WITHIN 48 HOURS OF FIRST APPEARANCE
FLU SYMPTOMS.
Oseltamivir and Zanamavir fall in the
Neuraminidase inhibitors class. The surface protein
Neuraminidase breaks bonds between new viruses and
infected cells. By blocking the activity of
Neuraminidase, these two drugs prevent the new viruses
from being released.
Another class of drugs - the M2
inhibitors is also available, but viruses develop
resistance to these drugs quickly and thus these drugs
may prove ineffective in controlling pandemics.
Amantadine and Rimantadine are two drugs from this
class. These drugs inhibit the activity of M2 protein,
which forms a channel in membranes of viruses and
thereby preventing the viruses from replicating.
One should consult a doctor before
taking any of these drugs as THESE DRUGS ARE KNOWN TO
HAVE SIDE EFFECTS IN SOME CASES. For example, Zanamavir
is not recommended to people having chronic respiratory
diseases such as asthma.
(This article was written on 25th
January 2006 and may not contain developments that took
place after this date.)
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