WHAT IS AVIAN FLU ("BIRD FLU") H5N1 INFECTION?
NEWS UPDATE: March, 2006: Avian flu is likely to spread to birds in the United States by midyear and could produce an epidemic among humans at any time, the United Nations official who monitors global efforts to fight the disease said.
"A lot of the human cases of bird flu have occurred in people under 25 and we're still not exactly sure why that is," said the WHO's Maria Cheng.
Children, teenagers
and young adults are the unfortunate victims of the deadly H5N1 bird flu
sweeping through poultry farms in Asia, Africa and now Europe.
Hooked up to breathing tubes and dialysis machines in local hospital beds,
bodies soaked in sweat, and blood oozing from their nostrils and mouth, they
have a mere 50 per cent chance of pulling through. The rest die in a matter of
days.
"We have a virus capable of replicating inside humans. We have a virus that
humans are not resistant to. We have a virus about which we don't understand
everything," said David Nabarro, a physician at the World Health Organization.
On September 30, 2005, the United
Nations World Health Organization (WHO) warned the world that an outbreak of
Avian influenza could kill 5 to 150 million people. Also, due to a bipartisan
effort of the United States Senate, $4 billion dollars was appropriated to
develop vaccines and treatments for Avian influenza.
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Avian influenza (also known as bird flu) H5N1 infection, is a type of influenza virulent in
birds. It was first identified in Italy in the early 1900s and is now known to
exist worldwide.
Infection
The causative agent is the avian influenza (AI) virus. AI viruses all belong to
the influenza virus A genus of the Orthomyxoviridae family and are
negative-stranded, segmented RNA viruses.
Avian influenza spreads in the air and in manure. Wild fowl often act as
resistant carriers, spreading it to more susceptible domestic stocks. It can
also be transmitted by contaminated feed, water, equipment and clothing;
however, there is no evidence that the virus can survive in well cooked meat.
Cats are also thought to be possible infection vectors for H5N1 strains of avian
flu (Kuiken et al, 2004).
The incubation period is 3 to 5 days. Symptoms in animals vary, but virulent
strains can cause death within a few days.
Subtypes pathogenic to humans
All Avian Influenza (AI) viruses are type A influenza viruses in the virus
family of Orthomyxoviridae and are subdivided into subtypes based on
hemagglutinin (H) and neuraminidase (N) protein spikes from the central virus
core. There are 16 H types, each with up to 9 N subtypes, yielding a potential
for 144 different H and N combinations. In addition, all AI viruses fall into
one of 2 pathotypes: low (LPAI) and high (HPAI) pathogenicity, based on how
dangerous to poultry.
Of the 16 H types known, only subtypes H5, H7 and H9 are known to be capable of
crossing the species barrier from birds to humans. It is feared that if the
avian influenza virus undergoes antigenic shift with a human influenza virus,
the new subtype created could be both highly contagious and highly lethal in
humans. Such a subtype could cause a global influenza pandemic, similar to the
Spanish Flu that killed over 20 million people in 1918 (though a variety of
sources quote average figures even higher, up to 100 million in some cases).
Many health experts are concerned that a virus that mutates to the point where
it can cross the species barrier (i.e. from birds to humans) will inevitably
mutate to the point where it can be transmitted from human to human. It is at
that point that a pandemic becomes likely.
More Books about Bird Flu
Influenza viruses that infect birds are called “avian influenza viruses.” Only
influenza A viruses infect birds. All known subtypes of influenza A virus can
infect birds.
However, there are substantial genetic differences between the subtypes that
typically infect both people and birds. Within subtypes of avian influenza
viruses there also are different strains (described in “Strains”). Avian
influenza H5 and H7 viruses can be distinguished as “low pathogenic” and “high
pathogenic” forms on the basis of genetic features of the virus and the severity
of the illness they cause in poultry; influenza H9 virus has been identified
only in a “low pathogenicity” form.
Since 1997 the following types of avian influenza virus has been confirmed to
outbreak infecting humans: H5N1, H7N2, H7N3, H7N7, and H9N2.
H5N1
H5N1 avian influenza strain passed from birds to humans in 1997 in Hong Kong.
Eighteen people were infected, of whom six died. The outbreak was limited to
Hong Kong. All chickens in the territory were slaughtered.
In January 2004, a major new outbreak of H5N1 avian influenza surfaced in
Vietnam and Thailand's poultry industry, and within weeks spread to ten
countries and regions in Asia, including Indonesia, South Korea, Japan and
mainland China. Intensive efforts were undertaken to slaughter chickens, ducks
and geese (over 40 million chickens alone were slaughtered in high-infection
areas), and the outbreak was contained by March, but the total human death toll
in Vietnam and Thailand was 23 people. In February 2004, avian influenza virus
was detected in pigs in Vietnam, increasing fears of the emergence of new
variant strains.
Fresh outbreaks in poultry were confirmed in Ayutthaya and Pathumthani provinces
of Thailand, and Chaohu city in Anhui, China, in July 2004.
In August 2004 avian flu was confirmed in Kampung Pasir, Kelantan, Malaysia. Two
chickens were confirmed to be carrying H5N1. As a result Singapore has imposed a
ban on the importation of chickens and poultry products. Similarly the EU has
imposed a ban on Malaysian poultry products. A cull of all poultry has been
ordered by the Malaysian government within a 10km radius of the location of this
outbreak.
An outbreak of avian influenza in January 2005 affected 33 out of 64 cities and
provinces in Vietnam, leading to the forced killing of nearly 1.2 million
poultry. Up to 140 million birds are believed to have died or were killed
because of the outbreak.
Vietnam and Thailand have seen several isolated cases where human-to-human
transmission of the virus has been suspected. In one case the original carrier,
who received the disease from a bird, was held by her mother for roughly 5 days
as the young girl died. Shortly afterwards, the mother became ill and perished
as well. In March, 2005 it was revealed that two nurses who had cared for avian
flu patients have tested positive for the disease.
In May 2005, the occurrence of Avian influenza in pigs in Indonesia was reported
("swine flu"). Along with the continuing pattern of virus circulation in
poultry, the occurrence in swine raises the level of concern about the possible
evolution of the virus into a strain capable of causing a global human influenza
pandemic. Health experts say pigs can carry human influenza viruses, which can
combine (i.e. exchange homologous genome sub-units by genetic reassortment.)
with the avian virus, swap genes and mutate into a form which can pass easily
among humans.
In July 2005, a death in Jakarta was the first confirmed human fatality in
Indonesia. The deaths of the man's two children, neither of whom were reported
to have had close contact with poultry, further raised concerns of
human-to-human transmission (although infection by eating undercooked poultry
may be a more likely explanation). As of July 20, the outbreak had claimed at
least 58 human lives — mostly in Vietnam. What concerns health researchers now
is that the virus mortality rate in Vietnam has dropped significantly lately,
from more than 65% to about 35% in a year. This might be a sign that the virus
is able to infect a larger number of people (i.e., the virus is able to spread
more easily) and possibly develop into a global pandemic with millions of deaths
despite the lower reported percentage of deaths. For example, the mortality rate
of 1918 Spanish flu (H1N1) pandemic was less than 5%. Also, in July 2005, it was
confirmed H5N1 had appeared in Russia's Novosibirsk region, probably carried by
migratory birds. On July 28th, avian influenza was reported to have killed two
more people in Vietnam, raising the death toll to 60. As of July 2005, most
human cases of avian influenza in East Asia have been attributed to consumption
of diseased poultry. Person-to-person transmission has not been unequivocally
confirmed in the outbreaks in East Asia.
In August 2005, scientists said they have successfully tested in people a
vaccine that they believe can protect against the strain of avian influenza that
is spreading in birds through Asia and Russia. Influenza A(H5N1) virus has
infected nearly 100 humans in the past 18 months, killing about half of them. If
the virus starts to spread efficiently among humans, experts fear it could
trigger a global pandemic that could kill millions. In response, millions of
birds throughout Asia have been slaughtered to try to stem the spread of the
virus; governments and the World Health Organization have been stockpiling
antiviral drugs, and scientists have been scrambling to produce an effective
vaccine. Due to the lag time needed to manufacture a vaccine that could prevent
deaths from a human influenza pandemic, Dr. Anthony S. Fauci, director of the
U.S. National Institute of Allergy and Infectious Diseases, announced that the
United States will order additional doses of the vaccine that is aimed at
containing a human pandemic, should it occur.
On August 3, 2005, the United Nations World Health Organization (WHO) said it
was following closely reports from China that at least 38 people have died and
more than 200 others have been made ill by a swine-borne disease in Sichuan
province. Sichuan Province, where infections with Streptococcus suis have been
detected in pigs in a concurrent outbreak, has one of the largest pig
populations in China. The outbreak in humans has some unusual features and is
being closely followed by the WHO. At that time, Chinese authorities say they
have found no evidence of human-to-human transmission.
Also in early August, an avian outbreak of influenza A(H5N1) was confirmed in
Kazakhstan and Mongolia, suggesting further spread of the virus. Later in
August, the virus was found in western Russia, marking its appearance in Europe.
In late September 2005, the UN health representative responsible for
coordinating a response to an outbreak, David Nabarro, stated that a flu
pandemic could happen at anytime and kill from five to 150 million people. He
further stated that as the virus had spread to migratory birds, an outbreak
could start in Africa or the Middle East, rather than southeast Asia as has been
widely assumed. At the same time, agricultural ministers of Association of South
East Asian Nations announced a three-year plan to counter the spread of the
disease.
H7N2
Following an outbreak of H7N2 among poultry in 2002 44 persons have been found
infected in Virginia, United States.
H7N3
In North America, the presence of avian influenza strain H7N3 was confirmed at
several poultry farms in British Columbia in February 2004. As of April 2004, 18
farms had been quarantined to halt the spread of the virus. Two cases of humans
with avian influenza have been confirmed in that region.
H7N7
In 2003 in Netherlands 89 people were confirmed to have H7N7 influenza virus
infection following an outbreak in poultry on several farms. One death has been
recorded.
H9N2
The virus type has been documented only in low pathogenic form. Three infections
in humans (China and Hong Kong) have been confirmed, all three patients
recovered.
Prevention and treatment
Avian influenza in humans can be detected with standard influenza tests.
However, these tests have not always proved reliable. In March 2005, the World
Health Organization announced that seven Vietnamese who initially tested
negative for bird flu were later found to have carried the virus. All seven have
since recovered from the disease. Currently (6/05) the most reliable test (microneutralization)
requires use of the live virus to interact with antibodies from the patient's
blood; because live virus is required, for safety reasons the test can only be
done in a level 3 laboratory.
Antiviral drugs are sometimes effective in both preventing and treating the
disease, but no virus has ever been really cured in medical history. Vaccines,
however, take at least four months to produce and must be prepared for each
subtype.
Further, as a result of widespread use of the antiviral drug amantadine as a
preventive or treatment for chickens in China starting in the late 1990's, some
strains of the avian flu virus in Asia have developed drug resistance against
amantadine [10]. Chickens in China have received an estimated 2.6 billion doses
of amantadine since early 2004. This use of amantadine for poultry goes against
international livestock regulations, but China kept it secret until recently, in
a manner reminiscent of the secrecy around the early spread of SARS.
Increasing virulence
In July 2004 a group of researchers led by H. Deng of the Harbin Veterinary
Research Institute, Harbin, China and Professor Robert Webster of the St Jude
Children's Research Hospital, Memphis, Tennessee, reported results of
experiments in which mice had been exposed to 21 isolates of confirmed H5N1
strains obtained from ducks in China between 1999 and 2002. They found "a clear
temporal pattern of progressively increasing pathogenicity". [11] Results
reported by Dr. Webster in July 2005 reveal further progression toward
pathogenicity in mice and longer virus shedding by ducks.
As of July 2005, most human cases of avian influenza in East Asia have been
attributed to consumption of diseased poultry. Person-to-person transmission has
not been unequivocally confirmed in the outbreaks in East Asia.
In May 2005, the occurrence of Avian influenza in pigs in Indonesia was reported
("swine flu"). Along with the continuing pattern of virus circulation in
poultry, the occurrence in swine raises the level of concern about the possible
evolution of the virus into a strain capable of causing a global human influenza
pandemic. Health experts say pigs can carry human influenza viruses, which can
combine (i.e. exchange homologous genome sub-units by genetic reassortment.)
with the avian virus, swap genes and mutate into a form which can pass easily
among humans.
On August 3, 2005, the United Nations World Health Organization (WHO) said it
was following closely reports from China that at least 38 people have died and
more than 200 others have been made ill by a swine-borne disease (possible "pig
flu" outbreak) in Sichuan province. Sichuan Province, where infections with
Streptococcus suis have been detected in pigs in a concurrent outbreak, has one
of the largest pig populations in China. The outbreak in humans has some unusual
features and is being closely followed by the WHO. At that time, Chinese
authorities say they have found no evidence of human-to-human transmission .
On September 30, 2005, the United
Nations World Health Organization (WHO) warned the world that an outbreak of
Avian influenza could kill 5 to 150 million people. Also, due to a bipartisan
effort of the United States Senate, $4 billion dollars was appropriated to
develop vaccines and treatments for Avian influenza.
Symptoms
In humans, it has been found that avian flu causes similar symptoms to other
types of flu :
fever
cough
sore throat
muscle aches
conjunctivitis
in severe cases of avian flu, it can cause severe breathing problems and
pneumonia, and can be fatal.
In one case, a boy with H5N1 presented to the hospital with diarrhea followed
rapidly by a coma without developing flu-like symptoms.[14]
Pandemic threat and preparedness plans
The World Health Organization (WHO) warns that there is a substantial risk of an
influenza pandemic within the next few years. One of the strongest candidates is
the A(H5N1) subtype of Influenza virus. WHO published a first edition of
the Global Influenza Preparedness Plan in 1999, and updated it in April 2005.
This is the first time a pandemic has been anticipated and is being prepared
for.
The aims of such plans are, broadly speaking, the following:
Before a pandemic, attempt to prevent it and prepare for it in case prevention
fails.
If a pandemic does occur, to slow its spread and allow societies to function as
normally as possible.
[edit]
Strategies to prevent a pandemic
If avian influenza remains an animal problem with limited human-to-human
transmission it is not a pandemic, though it continues to pose a risk.
To prevent the situation from progressing to a pandemic, the following
short-term strategies have been put forward:
Culling and vaccinating poultry
Limiting travel in areas where the virus is found
Longer term strategies proposed for regions where highly pathogenic H5N1 is
endemic in wild birds have included:
changing local farming practices to increase farm hygiene and reduce contact
between livestock and wild birds.
altering farming practices in regions where animals live in close, often
unsanitary quarters with people, and changing the practices of open-air "wet
markets" where birds are slaughtered in unsanitary conditions near fruits and
vegetables. Cock fighting also has played a role in spreading the disease by
bringing humans into contact with fowl, and this practice will also continue to
contribute to infection if it is not curbed. A challenge to implementing these
measures is widespread poverty, frequently in rural areas, coupled with a
reliance upon raising fowl for purposes of subsistence farming or income without
measures to prevent propagation of the disease.
changing local shopping practices from purchase of live fowl to purchase of
slaughtered, pre-packaged fowl.
improving veterinary vaccine availability and cost.
[edit]
Strategies to slow down a pandemic
Vaccines. A vaccine probably would not be available in the inital stages of
population infection. Once a potential virus is identified, it normally
takes at least several months before a vaccine becomes widely available, as it
must be developed, tested and authorised. The capability to produce vaccines
varies widely from country to country; in fact, only 15 countries are listed as
"Influenza vaccine manufacturers" according to the World Health Organisation. It is estimated that, in a best scenario situation, 750 million doses
could be produced each year, whereas it is likely that each individual would
need two doses of the vaccine in order to become inmuno-competent. Distribution
to and inside countries would probably be problematic. Several countries,
however, have well-developed plans for producing large quantities of vaccine.
For example, Canadian health authorities say that they are developing the
capacity to produce 32 million doses within four months, enough vaccine to
inoculate every person in the country. The United States has also taken
steps to produce an avian flu vaccine, which might be ready for mass production
by September 2005. In New Zealand, the Government has spent $26 million on
a preparedness program. The are catering for up to 1 million people affected,
and 20,000 hospitalized, in a population of 4 million. The Government requires
850,000 vacinations, and Roche cannot keep up with the demand.
Anti-viral drugs. Several new anti-viral drugs have been developed in recent
years. A number of governments are working to stockpile anti-viral drugs but the
work is complicated by the constant mutation of the virus, which might become
somewhat resistant to some anti-viral drugs, making these drugs less effective.
Non-pharmaceutical means:
"Social distance". By travelling less, working from home or closing schools
there is less opportunity for the virus to spread.
Respiratory etiquette. Placing one's hand in front of the mouth when coughing or
sneezing can somewhat limit the dispersal of droplets. However It has been
suggested recently that covering one's mouth and nose with one's hand is not
very effective in stopping the spread of germs as these germs are retained in
the hand, and are then deposited on doorknobs, on to others through handshakes,
etc. Current thinking suggests coughing or sneezing into the crook of one's arm
would be preferable to limit germ spread.
Masks. No mask can provide a perfect barrier but products that meet or exceed
the NIOSH N95 standard recommended by the World Health Organization are thought
to provide good protection. Other well-fitting masks can be helpful but much
less effective. Any mask may be useful to remind the wearer not to touch his
face. This can reduce infection due to contact with contaminated surfaces,
especially in crowded public places where coughing or sneezing people have no
way of washing their hands.
Hygiene. Frequent handwashing, especially when there has been contact with other
people or with potentially contaminated surfaces can be very helpful.
Stages 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.
As of early August 2005, most sources place the current avian influenza epidemic
at phase 3. There is ongoing debate as to the current phase. As of late
September 2005 consensus had not been reached on what the current phase should
be considered (between 3-5) based on the ongoing outbreaks in multiple countries
of southeast asia. The phases are defined as:
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
What is a
Pandemic?
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.
The source of this article is
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