Avian Influenza - Bird Flu FAQ
Avian Influenza - Bird Flu FAQ
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.)