Avian influenza
Author: Prof Celia Abolnik
Licensed under a Creative Commons Attribution license.
Introduction
presence of the virus to be notifiable to the World
Highly pathogenic notifiable avian influenza (HPNAI) is
Organization for Animal Health (OIE).
a serious, highly infectious and often lethal respiratory
disease of birds and some mammalian species,
Salient features of avian influenza
including humans, cats, dogs, and mink caused by
Common clinical signs of HPNAI infection in poultry
particular serotypes of the Influenza A virus.
are:
All serotypes of Influenza A virus are widespread in

quietness/ severe depression

slight to severe drop in egg production, with soft-
nature in wild ducks, geese and shorebirds, but
infection of these hosts does not usually produce
shelled or shell-less eggs

clinical signs. The virus replicates in the airways and in
respiratory difficulties such as coughing, sneezing,
sinusitis
the cells lining the intestinal tract, and is shed into the

nervous signs
environment though the nasal excretions and faeces.

swelling of the skin under the eye
Any susceptible host coming into contact with this can

swollen and/or congested wattles and combs
become infected. Poultry (fowls, turkeys, quail and

diarrhoea
ducks) are highly susceptible to infection with influenza

rapid spread with a mortality rate of up to 100%
A viruses but these can generally be classified into two
categories: low pathogenic avian influenza (LPAI)
viruses that typically cause little or no clinical signs in
within 48 hours

Sudden collapse and death with no preceding
clinical signs.
poultry, and highly pathogenic notifiable avian influenza
(HPNAI) viruses that can cause severe signs and high
mortalities in poultry. The term “notifable” refers to
viruses of the H5 an H7 serotypes, as these have the
potential to cause serious disease and epidemics.
The
various
serotypes
are
determined
by
the
combination of two major antigens coating the virus
surface, viz. the hemagglutinin (H) and neuraminidase
(N) glycoproteins. 16 different H and 9 different N types
have been discovered thus far, and can occur in any
combination to form the serotype, e.g. H5N1, H1N1
etc. However, only two of the “H” subtypes, viz. H5 and
H7 cause the scale of outbreaks that require the
Cyanosis of the wattles and combs
Where does avian influenza occur?
Vaccination can be applied to control the spread of
HPNAI potentially occurs all over the world, where the
HPNAI, but it cannot be used as a tool to eradicate
interface between wild birds and poultry is breached.
infection. Trade restrictions may apply if a country opts
This extends to poultry in contact with contaminated
to allow vaccination since “freedom from infection”
environmental water, since the viruses can remain
cannot be claimed.
viable for extended periods under certain conditions.
Maintaining poultry free from HPNAI is essential for the
What triggers an outbreak of avian influenza?
continuation of trade in poultry and poultry products
Outbreaks generally result from one of two scenarios:
between nations, and eradication by stamping out is

importation of infected birds or contamination by
still the preferred method for dealing with HPNAI. This
humans/ equipment from an infected location
is also applicable when LPNAI is diagnosed.
(possible introduction via migratory birds is also

included in this category)
Find out more
a discrete mutation event of LPNAI (H7 or H7) to
The CPD course will focus on an in-depth discussion of
HPNAI following introduction of LPNAI by wild
the characteristics of the Influenza A virus and other
birds to poultry.
factors that influence the severity of disease in the
host,
the
diagnostic
process,
and
epidemiology
including case studies from the African continent: the
outbreaks in Nigeria, Egypt and South Africa, and
surveillance
initiatives
in
wild
birds
across
the
continent. The socio-political and economic impacts of
the disease are also covered.
Disposing of culled ostrich carcasses during the
2004 HPNAI H5N2 outbreak in South Africa
Prevention and control

Keep poultry and wild birds separate, and do not
provide
open
feed
and
water
that
would
encourage contact

Control access to poultry houses by people and
equipment

Apply proper sanitation

Avoid introduction of birds of unknown disease
status into the flock

Dispose of infected carcasses properly.