ON HOW CAN BIRD FLU BE DETECTED?
Although there have been few human cases to
determine the exact incubation period of bird flu, it would be expected to be
from three to 10 days. The symptoms of bird flu in humans are similar to those
of regular influenza and include:
Complications Of Bird flu
Bird flu in humans can cause a range of serious and potentially fatal
including viral pneumonia
of the brain and heart.
Tell your doctor if you’ve
been to a country where there is bird flu
If you have recently returned from a country that had an outbreak of bird flu
and you get flu symptoms, see your doctor immediately. When making the
appointment, tell the clinic staff about your travel including any visits to
markets, farms or anywhere else where birds were present.
Influenza viruses can mutate
Influenza viruses that infect animal species can mutate and infect humans. The
human immune system may have no defences against viruses that previously only
infected animals. That’s why infection with these viruses can result in more
severe disease in people.
If the H5N1 bird flu virus were to mix with a human influenza virus, such a
‘combined’ virus could create a new human influenza virus that could spread
Health experts are concerned that the current bird flu affecting Asia could
become a worldwide pandemic if the virus does mutate. The worst influenza
pandemic in modern history was the Spanish flu, which occurred in 1918–19 and
killed up to 50 million people.
Measures to contain the spread of the current bird flu virus include
identifying and culling affected poultry flocks, research into tests and
vaccines, and rigorous quarantine practices.
Several antiviral medications used to treat human influenza are also effective
for bird flu. These could be used if a person developed symptoms after possible
exposure to bird flu, or to prevent illness in a person who was in close
contact with bird flu. Currently testing for bird flu vaccines is an ongoing
At the moment, there is no need for people living in USA, or people making
short visits to countries with cases of bird flu, to have antiviral
medications. Americans living long-term in countries affected by bird flu
should consider having a supply of antiviral medications in the home to use on
medical advice should the situation change while they are away from the US.
The Federal government is stockpiling Relenza and Tamiflu, two drugs that may
be used in the treatment of human cases of bird flu. In the case of an outbreak
in humans, these drugs would be used to maintain essential services, prevent
transmission and provide treatment for people who are already ill.
A vaccine against bird flu is in development, but is not currently available.
The current influenza vaccines will not protect humans against bird flu.
However, people who may be exposed to bird flu should consider being vaccinated
against human influenza viruses to reduce the risk of the viruses ‘mixing’ to
form a new flu strain.
Advice for travelers
Be aware of the risk of bird flu if you are travelling to a country where
outbreaks are occurring. Suggestions include:
contact with wild or domesticated birds such as chickens, ducks and geese.
Don’t go to farms or market places, since these are the primary carriers
of bird flu
- Stop young
children from putting contaminated objects or their own fingers into their
may be contaminated with bird faeces. Wash eggs thoroughly before breaking
and wash your hands thoroughly after handling eggs.
foods that contain uncooked egg, such as mayonnaise.
hands, chopping boards and utensils thoroughly after handling raw poultry.
poultry at high temperatures. Cooking temperatures of 80°C or higher
destroy the bird flu virus in about 60 seconds.
Control of avian
influenza A(H5N1): public health concerns
10 February 2004
The current outbreaks of highly pathogenic H5N1
avian influenza in poultry in parts of Asia have had immediate and severe
consequences for the agricultural sector.1 Human cases, with a high
fatality, have been reported in two countries, Viet Nam and Thailand, with very
widespread outbreaks in poultry.
It can be anticipated that human cases will also
be detected in other countries where outbreaks in poultry are rapidly
The number of human cases presently detected is
very small compared with the large number of infected birds distributed over a
wide geographical area. This suggests that the H5N1 virus strain may not easily
To date, no human-to-human transmission is known
to have occurred. However, the continuing presence of infection in poultry may
also create opportunities for the emergence of a new influenza virus subtype
with a capacity to spread easily among humans, thus marking the start of an
influenza pandemic. Should this rare event occur (three pandemics occurred
during the previous century), it would immediately have serious consequences
for human health throughout the world.
For this reason, public health concerns about the
present H5N1 situation must be given the highest priority when weighing the
immediate and measurable economic losses in animals against possible yet
unpredictable consequences for humans.
Several other diseases in animals can be
transmitted to humans. Experience with such diseases, known as “zoonoses”, has
shown that strict measures on animal health, imposed by the need to protect
human health, helped rebuild consumer confidence.2
Recent experience has also shown that measures
for the control of zoonotic diseases, aimed at halting further spread in
animals and minimizing economic losses, need to be closely coordinated with
measures that minimize the longer-term risks to human health. In the present
situation, measures aimed at eliminating the disease in poultry will also
reduce the presence of the virus in the environment and thus reduce
opportunities for human exposures and infections. These measures must be
carried out urgently, giving highest priority to the protection of human
health. Previous outbreaks of highly pathogenic avian influenza associated with
human infections occurred in areas, such as Hong Kong and the Netherlands, with
industrial poultry production and well developed health and agricultural
infrastructures. Even so, elimination of infection in poultry was a complex,
difficult, and costly undertaking. Both outbreaks were eventually controlled
through immediate culling of infected flocks, quarantine and disinfection of
farms, strict biosecurity, restrictions on the movement of animals, and
compensation for farmers.
The present situation is different. Control of
outbreaks of highly pathogenic avian influenza is known to be especially
difficult in areas where poultry range freely. In several affected countries,
up to 80% of the total poultry population is raised in small backyard farms.
Most rural families keep a small free-range flock.
Given these features of the present situation
there is potential that the H5N1 virus could become established in bird
populations in this geographical region and possibly spread to other parts of
the world. This was one of several conclusions reached during a joint FAO/OIE/WHO
technical consultation on the control of avian influenza, held in Rome from
No single blueprint for control in animals, and
thus reduction of risks for humans, is available. Over the past four decades,
only 18 outbreaks of highly pathogenic avian influenza, most caused by strains
other than H5N1, have occurred throughout the world. Existing evidence will not
suffice to provide universally applicable recommendations for a rapid and
effective response in affected countries.
Control measures must be tailored to each
country’s unique epidemiological situation and unique capacity, with health and
agricultural sectors working hand-in-hand. Agricultural authorities face the
immediate challenge of rapidly eliminating the H5N1 reservoir in poultry.
Authorities in all affected countries need to work together in a coordinated
Transparency in reporting of human and animal
disease is absolutely essential.
Despite the uncertainties, experts fully agree
that immediate culling of infected and exposed birds is the first line of
defence for both the protection of human health and the reduction of further
losses in the agricultural sector. Other measures, such as the vaccination of
healthy flocks, may play a supportive role in some cases when undertaken in
conjunction with measures for preventing further spread of infection. WHO has
repeatedly stressed the
need to ensure that culling is carried out in a way that does not fuel more
human cases. and that vaccination of poultry should not lead to the dropping of
vigilance or compromise other necessary control measures.
In responding to the situation, WHO emphasises
three strategic goals: to avert an influenza pandemic, to control the present
human outbreaks and prevent further spread, and to conduct the research needed
for better preparedness and response, including the immediate development of a
new vaccine for humans against H5N1. WHO has issued a series of technical
guidelines aimed at minimizing the risk of further human cases and
facilitating a coordinated international response.
1 Highly pathogenic avian influenza is
categorized by OIE as a “list A” disease. List A includes transmissible
diseases “which have the potential for very serious and rapid spread,
irrespective of national borders, which are of serious socio–economic or public
health consequence and which are of major importance in the international trade
of animals and animal products.”
2 One example is the spread of bovine spongiform
encephalopathy, or “mad cow disease”, in cattle, which led to the emergence of
a rare yet invariably fatal new disease in humans.
History of Avian Flu
The Avian Flu disease has captured considerable
international attention over the past year with serious epidemics of this
disease affecting Japan, South Korea, and areas of South-east Asia earlier this
year. Now considered a pandemic, serious outbreaks of avian influenza had
also affected the Netherlands, Belgium, and Germany in 2003. Avian flu had
also been reported in Australia, Pakistan, Italy, Chile, and Mexico. The
impact of this serious disease has been disruptive to the poultry industries as
millions of chickens, geese, and turkeys were slaughtered to prevent further
transmission of this highly contagious disease.
Besides its devastating effect on domestic
poultry, Avian Flu has received unprecedented publicity because of what
occurred in Hong Kong in 1997. Before this time, Avian flu was thought to
infect birds only, however, a different strain of Avian Flu virus was detected
in humans, marking the first time that Avian Flu was transmitted to
humans. During this outbreak, 18 people were hospitalized and 6 of them
died. To control the outbreak, authorities killed about 1.5 million
chickens to remove the source of the virus.
Earlier this year in January, a major outbreak of
Avian influenza surfaced again in Vietnam’s and Thailand’s poultry
industry. Within a few short weeks, the disease had spread to ten
countries and regions in Asia, including Indonesia, South Korea, Japan and
China. Over 50 million chickens, ducks, geese, and turkey were
slaughtered in an intensive effort to stop the disease from spreading any
further. The outbreak was then contained in March. Unfortunately,
this outbreak took a considerable toll on human lives. There were 34
people infected with the Avian Flu in Vietnam and Thailand, of which 23 of them
Though scientists determined that the spread of
the Avian flu virus from birds to humans are rare occurrences, they were also
quick to express grave caution that this problem could become significantly
worse if the virus mutated into a more lethal form, or a form that could pass
easily from humans to humans. The World Health Organization (WHO) is particularly
concerned about the Avian virus’ potential to swap genes with a common flu
virus, creating a lethal form of the virus that could spread around the globe
Avian Flu was first recorded in Italy more than
100 years ago in 1878. As the cause of massive poultry epidemics, this
disease was then known as “Fowl Plague”. This disease reared its ugly
head in the United States in 1924-25, and then again in 1929. In 1955, it
was determined that the virus causing Fowl Plague was one of the influenza
viruses. All influenza viruses affecting domestic animals (equine, swine,
avian) belong to Type A, and Type A influenza virus is the most common type
producing serious epidemics in humans. Types B and C do not affect domestic
There are two forms of Influenza A viruses
occurring worldwide – (i) highly pathogenic and (ii) mildly pathogenic.
The outbreaks in Hong Kong, and those that were found reported recently are
caused by the Highly Pathogenic Avian Influenza A virus (HPAI – subtypes H5 and
H7). It is a form of this virus that has the ability to be transmitted to
humans. Although our understanding of Avian Flu is relatively limited,
the recent outbreaks have stimulated research all around the world to further
our knowledge of this important disease and virus.
History of Avian Influenza
Confirmed instances of avian influenza viruses
infecting humans since 1997 include :
1997: In Hong Kong, avian influenza A (H5N1)
infected both chickens and humans. This was the first time an avian influenza
virus had ever been found to transmit directly from birds to humans. During
this outbreak, 18 people were hospitalized and 6 of them died.
1999: In Hong Kong, cases of avian influenza
A (H9N2) were confirmed in 2 children. Both patients recovered, and no
additional cases were confirmed. The evidence suggested that poultry was the
source of infection and the main mode of transmission was from bird to human.
2003: Two cases of avian influenza A (H5N1)
infection occurred among members of a Hong Kong family that had traveled to
China. One person recovered, the other died. How or where these 2 family
members were infected was not determined. Another family member died of a
respiratory illness in China, but no testing was done. No additional cases were
2003: Avian influenza A (H7N7) infections
among poultry workers and their families were confirmed in the Netherlands
during an outbreak of avian flu among poultry. More than 80 cases of H7N7
illness were reported (the symptoms were mostly confined to eye infections,
with some respiratory symptoms), and 1 patient died (in a veterinarian who had
visited an affected farm). There was evidence of some human-to-human
2003: H9N2 infection was confirmed in a child
in Hong Kong. The child was hospitalized but recovered.
of Avian Influenza
Clinical signs and post-mortal lesions may be
indicative of avian influenza infection. Virus isolation is needed for a
of the agent
birds – tracheal swabs and cloacal swabs or faeces
birds – organs and faeces
blood samples or
Identification of the Agent
Inoculation of 9-11-day-old embryonated chicken
eggs followed by:
immunodiffusion test to confirm the presence of influenza A virus
determination with monospecific antisera
- Strain virulence
evaluation: evaluation of the intravenous pathogenicity index (IVPI) in
antibodies to all AI virus, does not distinguish subtypes
suitable for testing chicken and turkey serum
- Within 1
week of infection, antibodies are detected in more than half the
AGID (Agar Gel Immunodiffusion
- As for
ELISA does not distinguish AI subtypes
- Within 1
week of infection, antibodies are detected in more than half the
HI (Haemagglutination Inhibition
available for each H subtype
- HI titres
are positive a few days later than ELISA or AGID, titres persist long
test for all avian species
IFT (Immunofluoresence test)
- Able to
detect antibodies to specific N-subtype
- Can be
used to detect infection in vaccinated birds if a heterologous vaccine is
used. Read more in Monitoring.
polymerase chain reaction)
- Able to
detect influenza virus at very low levels
presence of subtype H5 or H7 can be confirmed by using H5 or H7 specific
Influenza A Viruses Between Animals and People
Avian Flu: The Virus
& its Spread
Between Animal & People
A viruses have infected many different animals, including ducks, chickens,
pigs, whales, horses, and seals. However, certain subtypes of influenza A virus
are specific to certain species, except for birds, which are hosts to all known
subtypes of influenza A. Subtypes that have caused widespread illness in people
either in the past or currently are H3N2, H2N2, H1N1, and H1N2. H1N1 and H3N2
subtypes also have caused outbreaks in pigs, and H7N7 and H3N8 viruses have
caused outbreaks in horses.
A viruses normally seen in one species sometimes can cross over and cause
illness in another species. For example, until 1998, only H1N1 viruses
circulated widely in the U.S. pig population. However, in 1998, H3N2 viruses
from humans were introduced into the pig population and caused widespread
disease among pigs. Most recently, H3N8 viruses from horses have crossed over
and caused outbreaks in dogs.
influenza A viruses may be transmitted from animals to humans in two main ways:
- Directly from birds or from avian
virus-contaminated environments to people.
- Through an intermediate host, such as
A viruses have eight separate gene segments. The segmented genome allows
influenza A viruses from different species to mix and create a new influenza A
virus if viruses from two different species infect the same person or animal.
For example, if a pig were infected with a human influenza A virus and an avian
influenza A virus at the same time, the new replicating viruses could mix
existing genetic information (reassortment) and produce a new virus that had
most of the genes from the human virus, but a hemagglutinin and/or
neuraminidase from the avian virus. The resulting new virus might then be able
to infect humans and spread from person to person, but it would have surface
proteins (hemagglutinin and/or neuraminidase) not previously seen in influenza
viruses that infect humans.
type of major change in the influenza A viruses is known as antigenic shift.
Antigenic shift results when a new influenza A subtype to which most people
have little or no immune protection infects humans. If this new virus causes
illness in people and can be transmitted easily from person to person, an influenza
pandemic can occur.
possible that the process of genetic reassortment could occur in a human who is
co-infected with avian influenza A virus and a human strain of influenza A
virus. The genetic information in these viruses could reassort to create a new
virus with a hemagglutinin from the avian virus and other genes from the human
virus. Theoretically, influenza A viruses with a hemagglutinin against which
humans have little or no immunity that have reassorted with a human influenza
virus are more likely to result in sustained human-to-human transmission and
pandemic influenza. Therefore, careful evaluation of influenza viruses
recovered from humans who are infected with avian influenza is very important
to identify reassortment if it occurs.
it is unusual for people to get influenza virus infections directly from
animals, sporadic human infections and outbreaks caused by certain avian
influenza A viruses and pig influenza viruses have been reported. (For more
information see Avian
Influenza Infections in Humans .) These sporadic human infections and
outbreaks, however, rarely result in sustained transmission among humans.
Avian Influenza: Introduction
(AI) viruses infect domestic poultry and wild birds. In domestic poultry, AI
viruses are typically of low pathogenicity (LP), causing subclinical
infections, respiratory disease, or drops in egg production. However, a few
AI viruses cause severe systemic infections with high mortality. This highly
pathogenic (HP) form of the disease has historically been called fowl plague.
In most wild birds, AI viral infections are subclinical.
Clinical Findings and
Low Pathogenicity AI Viruses:
High Pathogenicity AI Viruses:
Avian influenza is an infectious disease of birds caused by
Other bird species, including domestic poultry, develop
In contrast, the second and far less common highly
All 16 HA (haemagluttinin) and 9 NA (neuraminidase)
To date, all outbreaks of the highly pathogenic form of
Not all virus strains of the H5 and H7 subtypes are highly
Apart from being highly contagious among poultry, avian
For highly pathogenic disease, the most important control measures
When culling – the first line of defence for containing
Apart from being difficult to control, outbreaks in
During 2005, an additional and significant source of
Evidence supporting this altered role began to emerge in
The outbreaks of highly pathogenic H5N1 avian influenza
In late July 2005, the virus spread geographically beyond
Prior to the present situation, outbreaks of highly
Influenza viruses are normally highly species-specific, meaning that viruses
Of all influenza viruses that circulate in birds, the H5N1
A second implication for human health, of far greater
The virus can improve its transmissibility among humans via
The second mechanism is a more gradual process of adaptive
During the first documented outbreak of human infections
All evidence to date indicates that close contact with dead
Investigations of all the most recently confirmed human cases, in China,
In many patients, the disease caused by the H5N1 virus follows an unusually
The incubation period for H5N1 avian influenza may be
Initial symptoms include a high fever, usually with a
One feature seen in many patients is the development of
In patients infected with the H5N1 virus, clinical
Limited evidence suggests that some antiviral drugs,
In suspected cases, oseltamivir should be prescribed as
Currently recommended doses of oseltamivir for the
As the duration of viral replication may be prolonged in
In severely ill H5N1 patients or in H5N1 patients with
Avian influenza: methods
Avian influenza, also known as bird flu, is a
While avian influenza caused by highly pathogenic
The OIE, through its experts and its world
The following information is meant to help
Message from Dr Bernard Vallat, OIE Director General –
Safety of International Trade
– Actual Newcastle
Vaccines and Diagnostic Methods
Methods of Humane Killing and Carcass
Description of the disease
Guidelines for Control of the Disease