Highly pathogenic avian influenza (HPAI)
was first reported in Southeast Asia in late 2003, although
the H5N1 virus is now considered to have emerged as early
as 1996 when it was first identified in geese in Guangdong
Province in southern China. Since then it has spread rapidly
and over large distances, with outbreaks occurring in domesticated
poultry and some wild bird populations in Mongolia, southern
Russia, the Middle East and, in 2005, in Europe and Africa.
Several epidemic waves have occurred in Indonesia, Thailand,
and Vietnam. The widespread practice of smallholder backyard
poultry keeping in these countries is frequently cited as
one of the primary risk factors for these outbreaks and the
persistence of the virus in domestic poultry populations.
Based on this assumption, some governments are considering
the prohibition of unconfined poultry flocks in order to increase
‘bio-security’ in smallholder backyard production.
HPAI thus constitutes a serious threat to poor rural smallholder
poultry producers, both directly, through mortality, but probably
even more so indirectly, through measures applied to control
the disease. These measures may be prohibitively expensive
for resource-poor smallholder producers and thus could force
them to abandon poultry keeping altogether, depriving them
of small but valuable amounts of protein in their diets, much
needed petty cash income, and, most importantly, an investment
opportunity for escaping poverty.
Given these likely adverse impacts of restrictive policies
on smallholder poultry growers, it is important to examine
the evidence base for such measures in terms of their effect
on risks of HPAI.
The Risk of HPAI in Backyard Flocks
There is an assumption that because the majority of HPAI
outbreaks have been reported in smallholder backyard flocks,
these operations are inherently more risky than other types
of poultry operations. This assumption was tested using published
data from the 2004 HPAI epidemic and concurrent active surveillance
programme in Thailand.
The Thai poultry sector is very heterogenous with commercial
broiler enterprises, consisting on average of 3,500 birds
per ‘flock’, constituting only two percent of
all ‘flocks’ but accounting for nearly sixty percent
of the standing poultry population. On the other hand, backyard
flocks, with an average flock size of 30 birds, constitute
approximately three quarters of flocks but account for only
around one fifth of the standing poultry population.
Estimation of the crude risk of HPAI infection in 2004 by
flock type as defined by the Thai animal health authorities,
showed that, for example, although layer flocks only constituted
one percent of all flocks, they accounted for five percent
of all registered infected flocks. Quail flocks showed the
highest risk of detected HPAI infection, nearly reaching 1.6
percent. Against widely held expectations, backyard flocks
showed the lowest risk of detected HPAI infection, 0.05 percent,
only one quarter that of layer and broiler flocks.
These results may reflect differences in ascertainment, HPAI
being more readily detectable by in large commercial operations
and more likely to be brought to the attention of animal health
authorities by these operators. However, since the active
surveillance programmes in place in Thailand were focused
on backyard operations, this potential ascertainment bias
is unlikely to be the main explanation for the higher risk
of HPAI detection in commercial layer and broiler flocks than
in backyard operations, and it appears warranted to review
the ‘bio-security’ of commercial operations.
Bio-Security of Commercial Poultry Operations
The confinement of large numbers of birds (as many as 50,000
in modern broiler houses in the US and Thailand), at very
high densities, poses significant challenges to ensuring bio-security.
(Bio-security being broadly defined as any system that prevents
the spread of infectious agents from infected to susceptible
Birds need to be supplied feed, water and air, and, because
confinement of thousands of animals requires controls to reduce
heat and regulate humidity, poultry houses require high volume
ventilation. This results in considerable movement of materials
from and into the external environment.
Campylobacter spp, for example, similar to HPAI virus, move
among avian host species, both domesticated and wild and in
both directions. The inability of conventional bio-security
measures to prevent the movement of Campylobacter in and out
of modern broiler facilities was clearly demonstrated in a
recent study of Campylobacter-free broiler flocks in the USA,
housed in sanitized facilities, using standard bio-security
measures, and fed Campylobacter-free feed and water.
Once a poultry flock is colonized with Campylobacter, the
food, water and air within the house quickly become contaminated
and the air exiting the house via ventilation systems becomes
a source of Campylobacter to the external environment. Campylobacter
strains with identical DNA fingerprints to those colonizing
broilers have been measured in air up to 30 m downwind of
broiler facilities housing colonized flocks.
There are additional mechanisms by which pathogens enter
and leave ‘bio-secure’ poultry houses. For example,
insects may carry microbes in and out of facilities through
ventilation systems and small openings as demonstrated in
a study in Denmark, which found that as many as 30,000 flies
may enter a broiler facility during a single flock rotation
in the summer months.
Another major challenge to bio-security arises through the
need to dispose of large amounts of animal waste from these
large poultry populations – each broiler chicken is
estimated to produce about 1.7 kg waste over its 6-7 week
life span, ie a 50,000 broiler unit produces nearly 2 tonnes
of waste per day. Land-disposed poultry house wastes are attractive
to wild birds due to the presence of spilled feed in these
wastes. These wild birds then may become infected and contaminate
water supplies of other poultry operations, thereby contributing
to large distance transmission.
The above provides ample evidence for the potential of pathogens
to move in and out of standard, reputedly bio-secure, commercial
poultry facilities, even in developed settings.
Individual versus Collective HPAI Risk
The risk of HPAI introduction into an individual flock is
determined by its ‘contact’ pattern and the risk
mitigation measures in place. Thus, although backyard poultry
keepers do not have bio-security measures in place, their
‘risky’ contacts, at least in Thailand, seem to
be rather limited, resulting in the counter-intuitive finding
that backyard poultry production is less risky, in terms of
HPAI infection, than production in larger and confined commercial
Collectively, however, simply as a result of their large
numbers, backyard poultry keepers will account for the majority
of infected flocks, thereby jeopardizing the sanitary status
of the poultry sector as a whole. Given the much stronger
political influence of commercial interests vis-à-vis
smallholder producers there is a clear danger that regulators
will opt for ‘easy’ solutions, such as imposing
measures to make subsistence poultry production ‘safer’,
eg forced housing or confinement of poultry. This will impose
very high costs, particularly upon a marginal group of entrepreneurs
and household producers and may lead to an overall reduction
of HPAI outbreaks, but more as a result of the loss of household
production flocks than as a result of enhanced bio-security.
The imposition of measures which do not significantly reduce
the risk of pathogen introduction and spread but place severe
economic burdens on society or groups thereof may be politically
opportune but is socially unjustifiable. Appropriate social
investments to reduce health risk locally and nationally,
which draw on the current global momentum for rapid and intensive
measures to control HPAI, can have the very significant dividend
of improving smallholder commercial viability, a pro-poor
benefit that stands in sharp contrast to the displacement
effects many of the proposed control strategies threaten to