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Avian Influenza
Influenza, or ‘flu’, comprises a large family of different
viruses, some of which affect humans and many of
which affect other animals, especially birds. Avian
Influenza, commonly known as ‘Bird Flu’, is an
infectious disease of birds.
There are many possible strains of the virus, most of
which do not infect humans. However, H5, H7 and H9
are the subtypes that have been causing most of the
recent illnesses in people; in particular H5N1 and
H7N9 (they are named according to which H and N
proteins exist on the surface of the virus).
As well as the medical concerns, Avian Influenza also has a severe economic impact on the livelihoods of
those involved in the poultry industry. Outbreaks cause the public to lose confidence in poultry products,
leading to a decrease in the consumption of chickens and turkeys for example. This also often leads to a
ban on importing from countries affected with the condition.
Natural History of Avian Flu
H5N1 was first reported to infect humans in 1993 during a poultry outbreak in Southern China and Hong
Kong, in which a high proportion of poultry died. In 1997, H5N1 shocked virologists when it killed 6 out of
18 people infected by poultry in Hong Kong. That outbreak was stopped when all 1.2 million poultry in
Hong Kong were slaughtered. There were further outbreaks in 2003 and 2004 resulting in spread of the
virus to Europe and Africa.
Between 2003 and July 2014 there were 667 confirmed human cases of H5N1 infection in 15 countries,
leading to a total of 393 deaths.
Another strain of Avian Influenza, H7N9, first infected humans in parts of China in 2013, causing high
infection rates and scores of deaths. This strain has become entrenched in those regions. Unusually, this
strain does not appear to kill poultry making it much more difficult for surveillance purposes.
Key Points
 There are lots of different types of bird flu and most are harmless to people
 H5N1 Avian Influenza is a highly infectious disease of birds that can be spread to people,
but is difficult to transmit from person to person
 Almost all people with H5N1 infection have had close contact with infected birds or
contaminated environments
 When people do become infected, the mortality rate is about 60%
 Early treatment with Tamiflu can shorten disease length and prevent serious complications
 A possible genetic mutation leading to human-to-human transmission could lead to a
pandemic outbreak
 Mutations making the disease less virulent are just as likely, however.
Spread
Avian Influenza is found in a wide range of wild waterfowl, such as ducks and geese, often causing no
apparent illness. These birds can migrate long distances and have the capacity to spread the virus far and
wide. Once Avian Influenza spreads to domestic poultry populations, which are frequently densely
populated, there is the potential for large-scale outbreaks of the disease.
Within a country, the disease spreads easily from farm to farm. Large amounts of virus are secreted in bird
droppings, contaminating dust and soil. Airborne virus can spread the disease from bird to bird, causing
infection when the virus is inhaled. Contaminated equipment, vehicles, feed, cages or clothing - especially
shoes - can carry the virus from farm to farm. The virus can also be carried on the feet and bodies of other
animals, such as rodents, which act as "mechanical vectors" for spreading the disease.
The most important control measures during outbreaks are as follows:
Rapid destruction of all infected or exposed birds
Proper disposal of carcasses
Quarantining and rigorous disinfection of farms and poultry markets
Limiting the movement of commercial poultry, both domestically and internationally.
Over the last 20 years, tens of millions of chickens, ducks and turkeys have died or been culled in farms
across Southeast Asia because of the H5N1 virus. These measures require a coordinated approach
between animal and public health authorities.
Vaccination of poultry has also been successfully used. However, it is impractical outside of large-scale
commercial settings, too costly to implement in resource-poor countries, and the vaccine requires regular
updating.
The primary risk factor for human infection appears to be direct or indirect exposure to infected live or
dead poultry, or contaminated environments. Birds shed the influenza virus in their faeces and therefore
contact with bird droppings is also a possible transmission route. The illness mainly affects workers in the
poultry industry, such as farmers who need to muck out and handle poultry, haulage workers involved in
transport of poultry, and workers in live bird markets.
Person-to-person transmission, however, is inefficient and very rare, involving very close and sustained
contact such as that between a mother and her sick child.
There is no evidence to suggest that these viruses can be transmitted to humans through properly
prepared poultry or eggs.
Clinical Features
The fatality from Avian Influenza in humans is much higher than
that of seasonal influenza infections. The incubation period for
H5N1 ranges from 2 days to as long as 17 days.
Diagnosis is by isolation of the virus in nose and throat swabs,
as well as by the use of a chest X-Ray and blood tests.
There is mounting evidence that the H5N1 strain has the
capacity to jump the species barrier and infect many species.
When doing so, it causes unusually severe disease, with high
mortality in humans.
Early symptoms
 High fever
 Cough, sore throat, muscle aches
 Diarrhoea, vomiting, abdominal
pain.
More severe disease
 Respiratory distress
 Lung infection leading to
pneumonia and bloody sputum
 Multi-organ failure, seizures and
death.
Treatment
Evidence suggests that particular antiviral drugs (notably Tamiflu), when given early in the course of the
illness, can reduce the severity of disease and improve prospects of survival. Infected people are likely to
require hospital admission, often in intensive care units. The mortality rate is up to 60%. Vaccines are
being trialed but are not yet ready for widespread use.
There is no protection offered by the routine seasonal influenza vaccine.
Pandemic Potential
Pandemic influenza emerges as a result of a new flu virus, which is markedly different from recently
circulating strains. Few people, if any, will have immunity to this new virus thus allowing it to spread easily
and to cause more serious illness. The conditions that allow a new virus to develop and spread continue to
exist, and some features of modern society, such as air travel, could accelerate the rate of spread.
In order for Avian Influenza to cause a pandemic, with outbreaks affecting large parts of the world, an
influenza virus would have to emerge with the ability to cause sustained human-to-human transmission in
a population with little or no immunity to the virus. The main concern expressed by health experts is that
the highly unstable H5N1 avian flu virus might possibly change or mutate into a new, deadly form of human
influenza. If this were to adapt, so that it could easily be passed from human to human, the world could be
faced with an influenza pandemic.
Current Concerns
There have been six confirmed human cases of H5N1 in Egypt this year, with one fatality to date. Avian
Influenza is consistently present in Egypt with frequent outbreaks in poultry - since 2006, over 170 human
cases of bird flu have been confirmed, of which around 65 were fatal.
On 6 November 2014, German authorities reported an outbreak of the highly pathogenic Avian Influenza
virus, H5N8, at a turkey holding. Environmental health authorities immediately ordered the culling of the
turkeys at the affected holding, protection and surveillance zones were established, and investigations
initiated to establish how the birds became infected. This strain of Avian Influenza has also recently been
identified on farms in the Netherlands and the UK. The most likely route of infection is through migratory
birds heading south for the winter and contaminating the poultry farms’ bird feed.
This virus has also been detected among wild birds in South-East Asia where it has also caused several
outbreaks on commercial poultry farms in South Korea and China.
The two recent cases of H7N9, reported and treated effectively in Canada, are the first instances of
infection occurring outside of the Far East. Although concerning, both patients give a clear history of recent
travel to China and of having been exposed to infected poultry; these infections do not represent an
emerging epidemic, as human to human transmission appears to remain an unlikely and difficult event.
Avian Influenza, with its frequent genetic mutation and widespread penetration in the wild bird population,
may never be effectively eradicated. However, the World Health Organization has set out strict public
health measures that must be universally employed if the spread of the disease is to be limited and the
dangers of human infection reduced.
Sources
World Health Organization
www.who.int/influenza/human_animal_interface/en/
European Centre for Disease Control
http://www.ecdc.europa.eu/en/publications/Publications/avian-influenza-AH5N8-Germany-riskassessment.pdf
Public Health England
https://www.gov.uk/government/organisations/public-health-england
New Scientist
http://www.newscientist.com/article/dn25713-wild-bird-flu-could-mutate-into-deadly-humanpandemic.html#.VGyGOIdRV1M
____________________________________________________________________________________________________________
Written by Dr Adrian Hyzler MBChB MBA
Senior Medical Officer, Healix International
© Healix International 2015.
All rights reserved.
th
Published 16 April, 2015
E: [email protected]
www.healix-international.com
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