The Flu Virus! One of the most dreadful
lethal virus of the Universe. This Influenza virus is infectious to all
species of animals and birds: Human Influenza, Swine Influenza, Equine
Influenza, Avian Flu etc are the different names.
KNOW THE PAST….
Bird flu was first identified in Italy more than 100
years ago. The flu outbreaks are not uncommon. Within the species, when
affected they are not so dangerous. Usually they do not spread to humans.
But occasionally happens with a sudden change in genotype of the virus which
is unfamiliar to human immune system to resist. The history tells the
fearful truths which are beyond imagination for the present generation.
Year of outbreak
Name of outbreak
Spanish Flu Pandemic
40-50 million people died
100,000 Americans died
Hong Kong Flu
50 million affected of which 70,000 died in
United states of America.
First human case of bird flu infection occurred in May
1997, in a 3 year old boy who died of the disease. In 1999 a different
strain of bird flu virus identified as A (H9N2) infected two people in Hong
Kong. They recovered by treatments.
In 2003, one person died from bird flu virus A (H5N1)
in Asia out of two reported infection. Both belonged to the same family from
Hong Kong. In April 2003, a Dutch veterinarian working in a farm infected
with bird flu virus of H7 strain died of pneumonia. The Vet did not take any
medication against bird flu or human flu. Again in 2003 bird flu virus A
(H7N7) infected 80 people in Netherlands killing one.
During this outbreak, there were signs of human–human transmission of the
disease – a rare event. So far in 2004 WHO reports 23 casualties of H5N1
outbreaks in Asia. Eight of these in Thailand and 15 in Vietnam. During
2003-05 period the A (H5N1) strain of bird flu virus infected 117 people out
of which 64 died.
Europeans are getting worried because the Avian flu is moving
westward (through Asia) carried by flocks of waterfowl. UPDATE- 13th
Outbreak of bird flu has been reported from Cambodia, China,
Indonesia, Japan, Laos, and South Korea during the last few years. None of
these infected humans.
During 1997, 1.5 million
poultry were culled and destroyed in Hong Kong within 3 days, which would
have averted a human pandemic. WHO reports flu pandemics can be expected to
occur three or four times every 100 years. Experts say ‘another Influenza
pandemic is inevitable and possibly imminent ‘.
Bird flu virus is an RNA virus, which
resembles a short rod studded with two kinds of protein spikes such as the
Haemagglutinin (H) and Neuraminidase (N).
STRUCTURE OF FLU VIRUS
There are 3 general types of flu viruses distinguished
with their capsid (inner membrane) proteins as Type A, B and C. Type A flu
virus cause most serious flu epidemics in humans, other mammals and birds.
Type B and C viruses are restricted to humans and cause only mild
More than 20 strains of Influenza A viruses are identified, based on their
difference in protein spikes. There are 13 distinct H subtypes and 9
distinct N subtypes each of which require a different vaccine to protect
against infection. Type A virus that caused the 1968 Hong Kong flu epidemic
has type 3 H protein molecules and Type 2 N protein molecules and is called
A (H3N2). The bird flu virus, which passed to humans directly from bird, is
with Type 5 H protein and type 1 N protein. Hence, it is called A (H5N1).
This is identified in chicken in 1961.
Haemagglutinin (H) protein aids the virus in gaining access to the host cell
Interior. The Neuraminidase (N) help the daughter virus break free of host
cell once the virus Replication is completed. The H molecule has three
strands fixed on the surface of virus particle like a tripod with a club
like projection on the top. Each has ‘hotspots‘ that display an unusual
tendency to change as a result of mutation of the virus RNA during
imprecise replication sometimes. These segments of H molecule functions as
targets against which the body’s antibodies are directed. New strains of flu
virus arise not through mutation but through recombination of genes. This
may lead to novel combinations of H and N spikes unrecognizable by the human
antibodies which are specific for the old configuration.
Viral recombination of this type seem to have been
responsible for the past three major flu pandemics. Public health officials
remain concerned that the genes of Influenza A (H5N1) strain virus which is
slightly infectious to human beings could yet mix with a human strain
to create a new strain that could spread widely in human population.
The experts say this could lead to the first flu pandemic of the 21st
Influenza viruses are generally
thought to evolve via shifting and drifting. Shifting occurs when viruses
swap genes and drifting was thought to be due to steady accumulation of
US Centre for Disease Control points out two chances of greater threats to
Humans with the bird flu virus: First, the genetic material of the bird flu
virus could evolve by recombination of genes giving rise to new more
virulent strains by changing combinations of H and N subtype molecules.
(i.e., H1, H2……H 13 and N1, N2…..N9 combinations).
Second chance is the bird flu virus could combine
its genetic material with other Influenza viruses that already infect
humans. The chances are more in cases where humans are in close contact with
Both avian and human influenza viruses
can infect pigs (Swine influenza). Swine Influenza outbreak was there in USA
just after the human flu pandemic of 1918-19. In pigs this create a
genetic ‘ melting pot ‘ in which different strains of viruses can swap
their genes and acquire each others properties to evolve a new strain.
Rapidly evolving viruses simply recycle old mutations via
recombination. This is more efficient. This happens in most type of viruses
including influenza, HIV, SARS, Foot and Mouth Disease virus of cattle etc.
This necessitates vaccines to be prepared before the viruses emerge.
Fifteen subtypes of influenza viruses are known to infect birds thus
providing an extensive reservoir of influenza viruses potentially
circulating in bird population.
So far the identified flu viruses from
previous outbreaks are Type A(H1N1) ,H2N2, H3N2, H5N1, H9N2 H7N7.
Bird flu or avian flu is thus another
zoonotic disease, which can be transmitted to Human beings from birds and
animals and vice versa.
ROUTES OF FLU VIRUS...
Flu epidemics are often in Asia. New strains
originate in the Far East. Most common host for influenza viruses are duck,
chickens and pigs which in Asia live in close proximity to each other and to
humans. Pigs are subjected to infection by both human and bird strain. Also
may be infected with multiple strains. This creates conditions favoring
genetic recombination between strains.
The Hong Kong Flu arose from
recombination between A (H3N8) from ducks and A(H2N2) from humans. The
strain produced was A (H3N2) then passed back to humans creating an epidemic
because human population has never experienced that H3N2 combination A
EVOLUTION OF NEW STRAINS...
Disease can be transmitted to humans from wild birds
and chickens. Unless there is strain variation the bird flu virus does not
appear to spread easily from person to person. Infected birds spread the
virus through saliva, faeces and nasal secretions. Wild and migrating birds
act as carriers and spread the disease to very far away places within a
short span of time. So far, humans with close contact with sick birds only
caught infection with bird flu. There is no evidence till now that the virus
is being spread through eating chicken products. Heat kills the virus.
Chicken should be cooked thoroughly at temperature at least 70 degree C (158
degree F). People should wash their hands after handling poultry and ensure
that poultry carcasses and waste do not contaminate other objects. The Flu
virus can survive up to 4 days at 22 degree C (71 degree F) and more than 30
days at 0 degree C (32 degree F). If frozen, it can survive indefinitely.
Affected birds show...
If the strain is virulent mortality rate can
range between 50-100 %.
human beings, symptoms are
ANTI VIRAL DRUGS AGAINST BIRD FLU...
Recent outbreaks in Asia have been found to be resistant to the oldest and
cheapest anti flu drugs Rimantidine and Amantidine. Australian Researchers
say Relenza (Zanamivir) and Tamiflu (Oseltamivir) are effective treatments
against flu. Anti viral drugs are expensive and in limited supply.
THE DISEASE CAN BE PREVENTED
Culling of suspected poultry population and putting infected farms in
quarantine .Another method is vaccination of birds against flu virus but
this is controversial. In efficient vaccines may allow the virus to
replicate without the animal showing any symptoms, a phenomena known as
‘silent epidemic’, which can be dangerous. However, Indonesia has launched a
poultry vaccination drive and Thailand is considering the same course of
WHO recommends that people at high risk of exposure with bird flu virus,
mainly people involving culling operations should be vaccinated with most
recent human flu vaccine available. Situations for simultaneous infection
with bird flu and human flu virus should be avoided. Wild migrating birds
play a role in spreading the bird flu. However, UN Food and Agricultural
Organization has recommended that culling wild bird population is not
Movement of live poultry should also be strictly regulated. Strict
surveillance and monitoring by the concerned state departments is essential.
People working in poultry farms and slaughterhouses, swimming in
contaminated rivers and ponds, playing in an area where carcasses were
buried, staying near poultry processing plants etc can lead to infection.
Disposal of broiler chicken waste in open places must be prohibited.
Suitable protective measures and avoiding predisposing conditions are
advised. Controlled vast slaughter of suspected birds in an outbreak will
contain the virus that spread by air, water and soil.
The arrival of poultry from other states must be inspected thoroughly by
qualified persons supporting with clinical laboratory tests. Disease
Investigation Wing of the Animal Husbandry Department and Veterinary
Colleges should be equipped well to detect and control the bird flu virus
infection. Poultry and pig farms must be frequently inspected to detect flu.
Even though the warm climate and cooking habits protect us from bird flu,
the flu virus can at any time change their genotype to adapt to new
conditions and can lead to a pandemic.
Dr. Jamie Love, Avian Flu,
Virus Pictures-Russel Kightely Media: Scientific Illustration.