Avian influenza, known informally as avian flu or bird flu, is a variety of influenza caused by viruses adapted to birds. The type with the greatest risk is highly pathogenic avian influenza (HPAI). Bird flu is similar to swine flu, dog flu, horse flu and human flu as an illness caused by strains of influenza viruses that have adapted to a specific host. Out of the three types of influenza viruses (A, B, and C), influenza A virus is a zoonotic infection with a natural reservoir almost entirely in birds. Avian influenza, for most purposes, refers to the influenza A virus.
Though influenza A is adapted to birds, it can also stably adapt and sustain person-to-person transmission. Recent influenza research into the genes of the Spanish flu virus shows it to have genes adapted from both human and avian strains. Pigs can also be infected with human, avian, and swine influenza viruses, allowing for mixtures of genes (reassortment) to create a new virus, which can cause an antigenic shift to a new influenza A virus subtype which most people have little to no immune protection against.
Avian influenza strains are divided into two types based on their pathogenicity: high pathogenicity (HP) or low pathogenicity (LP). The most well-known HPAI strain, H5N1, appeared in China in 1996, and also has low pathogenic strains found in North America. Companion birds in captivity are unlikely to contract the virus and there has been no report of a companion bird with avian influenza since 2003. Pigeons can contract avian strains, but rarely become ill and are incapable of transmitting the virus efficiently to humans or other animals.
Between early 2013 and early 2017, 916 lab-confirmed human cases of H7N9 were reported to the World Health Organization (WHO). On 9 January 2017, the National Health and Family Planning Commission of China reported to WHO 106 cases of H7N9 which occurred from late November through late December, including 35 deaths, 2 potential cases of human-to-human transmission, and 80 of these 106 persons stating that they have visited live poultry markets. The cases are reported from Jiangsu (52), Zhejiang (21), Anhui (14), Guangdong (14), Shanghai (2), Fujian (2) and Hunan (1). Similar sudden increases in the number of human cases of H7N9 have occurred in previous years during December and January.
History
The
most widely quoted date for the beginning of recorded history of avian
influenza (initially known as fowl plague) was in 1878 when it was
differentiated from other diseases that caused high mortality rates in
birds. Fowl plague, however, also included Newcastle disease
until as recently as the 1950s. Between 1959 and 1995, there were 15
recorded occasions of the emergence of HPAI viruses in poultry, but
losses were minimal. Between 1996 and 2008 however, HPAI outbreaks in
poultry have occurred at least 11 times and 4 of these outbreaks have
involved millions of birds.
In the 1990s, the world's poultry population grew 76% in
developing countries and 23% in developed countries, contributing to the
increased prevalence of avian influenza.
Before the 1990s, HPAI caused high mortality in poultry, but infections
were sporadic and contained. Outbreaks have become more common due to
the high density and frequent movement of flocks from intensive poultry production.
Influenza A/H5N1 was first isolated from a goose in China in 1996. Human infections were first reported in 1997 in Hong Kong. Since 2003, more than 700 human cases of Asian HPAI H5N1 have been reported to the WHO,
primarily from 15 countries in Asia, Africa, the Pacific, Europe, and
the Middle East, though over 60 countries have been affected.
Genetics
Genetic factors in distinguishing between "human flu viruses" and "avian flu viruses" include:
- PB2: (RNA polymerase): Amino acid (or residue) position 627 in the PB2 protein encoded by the PB2 RNA gene. Until H5N1, all known avian influenza viruses had a Glu at position 627, while all human influenza viruses had a Lys.
- HA: (hemagglutinin): Avian influenza HA viruses bind alpha 2-3 sialic acid receptors, while human influenza HA viruses bind alpha 2-6 sialic acid receptors. Swine influenza viruses have the ability to bind both types of sialic acid receptors. Hemagglutinin is the major antigen of the virus against which neutralizing antibodies are produced, and influenza virus epidemics are associated with changes in its antigenic structure. This was originally derived from pigs, and should technically be referred to as "pig flu".
Subtypes
There
are many subtypes of avian influenza viruses, but only some strains of
five subtypes have been known to infect humans: H5N1, H7N3, H7N7, H7N9,
and H9N2. At least one person, an elderly woman in Jiangxi Province, China, died of pneumonia in December 2013 from the H10N8 strain, the first human fatality confirmed to be caused by that strain.
Most human cases of the avian flu are a result of either handling
dead infected birds or from contact with infected fluids. It can also
be spread through contaminated surfaces and droppings. While most wild
birds have only a mild form of the H5N1 strain, once domesticated birds
such as chickens or turkeys are infected, H5N1 can potentially become
much more deadly because the birds are often in close contact. H5N1 is a
large threat in Asia with infected poultry due to low hygiene
conditions and close quarters. Although it is easy for humans to
contract the infection from birds, human-to-human transmission is more
difficult without prolonged contact. However, public health officials
are concerned that strains of avian flu may mutate to become easily
transmissible between humans.
Spreading of H5N1 from Asia to Europe is much more likely caused
by both legal and illegal poultry trades than dispersing through wild
bird migrations, being that in recent studies, there were no secondary
rises in infection in Asia when wild birds migrate south again from
their breeding grounds. Instead, the infection patterns followed
transportation such as railroads, roads, and country borders, suggesting
poultry trade as being much more likely. While there have been strains
of avian flu to exist in the United States, they have been extinguished
and have not been known to infect humans.
Examples of avian influenza A virus strains:
| HA subtype designation |
NA subtype designation |
Avian influenza A viruses |
|---|---|---|
| H1 | N1 | A/duck/Alberta/35/76(H1N1) |
| H1 | N8 | A/duck/Alberta/97/77(H1N8) |
| H2 | N9 | A/duck/Germany/1/72(H2N9) |
| H3 | N8 | A/duck/Ukraine/63(H3N8) |
| H3 | N8 | A/duck/England/62(H3N8) |
| H3 | N2 | A/turkey/England/69(H3N2) |
| H4 | N6 | A/duck/Czechoslovakia/56(H4N6) |
| H4 | N3 | A/duck/Alberta/300/77(H4N3) |
| H5 | N3 | A/tern/South Africa/300/77(H4N3) |
| H5 | N4 | A/Ethiopia/300/77(H6N6) |
| H5 | N8 | H5N8 |
| H5 | N9 | A/turkey/Ontario/7732/66(H5N9) |
| H5 | N1 | A/chick/Scotland/59(H5N1) |
| H6 | N2 | A/turkey/Massachusetts/3740/65(H6N2) |
| H6 | N8 | A/turkey/Canada/63(H6N8) |
| H6 | N5 | A/shearwater/Australia/72(H6N5) |
| H6 | N1 | A/duck/Germany/1868/68(H6N1) |
| H7 | N7 | A/fowl plague virus/Dutch/27(H7N7) |
| H7 | N1 | A/chick/Brescia/1902(H7N1) |
| H7 | N9 | A/chick/China/2013(H7N9) |
| H7 | N3 | A/turkey/England/639H7N3) |
| H7 | N1 | A/fowl plague virus/Rostock/34(H7N1) |
| H8 | N4 | A/turkey/Ontario/6118/68(H8N4) |
| H9 | N2 | A/turkey/Wisconsin/1/66(H9N2) |
| H9 | N6 | A/duck/Hong Kong/147/77(H9N6) |
| H9 | N6 | A/duck/Hong Kong/147/77(H9N6) |
| H9 | N7 | A/turkey/Scotland/70(H9N7) |
| H10 | N8 | A/quail/Italy/1117/65(H10N8) |
| H11 | N6 | A/duck/England/56(H11N6) |
| H11 | N9 | A/duck/Memphis/546/74(H11N9) |
| H12 | N5 | A/duck/Alberta/60/76/(H12N5) |
| H13 | N6 | A/gull/Maryland/704/77(H13N6) |
| H14 | N4 | A/duck/Gurjev/263/83(H14N4) |
| H15 | N9 | A/shearwater/Australia/2576/83(H15N9) |
Spread
Birds that have died of avian influenza. The virus is spread by contact between healthy and unhealthy birds.
Avian influenza is most often spread by contact between infected and
healthy birds, though can also be spread indirectly through contaminated
equipment.
The virus is found in secretions from the nostrils, mouth, and eyes of
infected birds as well as their droppings. HPAI infection is spread to
people often through direct contact with infected poultry, such as
during slaughter or plucking.
Though the virus can spread through airborne secretions, the disease
itself is not an airborne disease. Highly pathogenic strains spread
quickly among flocks and can destroy a flock within 28 hours; the less
pathogenic strains may affect egg production but are much less deadly.
Although it is possible for humans to contract the avian
influenza virus from birds, human-to-human contact is much more
difficult without prolonged contact. However, public health officials
are concerned that strains of avian flu may mutate to become easily
transmissible between humans.
Some strains of avian influenza are present in the intestinal tract of
large numbers of shore birds and water birds, but these strains rarely
cause human infection.
Five manmade ecosystems have contributed to modern avian
influenza virus ecology: integrated indoor commercial poultry,
range-raised commercial poultry, live poultry markets, backyard and
hobby flocks, and bird collection and trading systems including cockfighting.
Indoor commercial poultry has had the largest impact on the spread of
HPAI, with the increase in HPAI outbreaks largely the result of
increased commercial production since the 1990s.
Village poultry
In
the early days of the HPAI H5N1 pandemic, village poultry and their
owners were frequently implicated in disease transmission. Village poultry, also known as backyard and hobby flocks, are small flocks raised under extensive
conditions and often allowed free range between multiple households.
However, research has shown that these flocks pose less of a threat than
intensively raised commercial poultry with homogenous genetic stock and poor biosecurity.
Backyard and village poultry also do not travel great distances
compared to transport of intensively raised poultry and contribute less
to the spread of HPAI.
This initial implication of Asian poultry farmers as one broad category
presented challenges to prevention recommendations as commercial
strategies did not necessarily apply to backyard poultry flocks.
H5N1
The highly pathogenic influenza A virus subtype H5N1 is an emerging avian influenza virus that is causing global concern as a potential pandemic threat. It is often referred to simply as "bird flu" or "avian influenza", even though it is only one of many subtypes.
H5N1 has killed millions of poultry in a growing number of
countries throughout Asia, Europe, and Africa. Health experts are
concerned that the coexistence of human flu viruses and avian flu
viruses (especially H5N1) will provide an opportunity for genetic
material to be exchanged between species-specific viruses, possibly
creating a new virulent influenza strain that is easily transmissible
and lethal to humans. The mortality rate for humans with H5N1 is 60%.
Since the first human H5N1 outbreak occurred in 1997, there has
been an increasing number of HPAI H5N1 bird-to-human transmissions,
leading to clinically severe and fatal human infections. Because a
significant species barrier exists between birds and humans, the virus
does not easily spread to humans, however some cases of infection are
being researched to discern whether human-to-human transmission is
occurring.
More research is necessary to understand the pathogenesis and
epidemiology of the H5N1 virus in humans. Exposure routes and other
disease transmission characteristics, such as genetic and immunological
factors that may increase the likelihood of infection, are not clearly
understood.
The first known transmission of H5N1 to a human occurred in Hong Kong
in 1997, when there was an outbreak of 18 human cases; 6 deaths were
confirmed. None of the infected people worked with poultry. After
culling all of the poultry in the area, no more cases were diagnosed.
In 2006, the first human-to-human transmission likely occurred when 7
members of a family in Sumatra became infected after contact with a
family member who had worked with infected poultry.
Although millions of birds have become infected with the virus
since its discovery, 359 people have died from H5N1 in twelve countries
according to World Health Organization reports as of August 10, 2012.
As an example, the H5N1 outbreak in Thailand
caused massive economic losses, especially among poultry workers.
Infected birds were culled and slaughtered. The public lost confidence
with the poultry products, thus decreasing the consumption of chicken
products. This also elicited a ban from importing countries. There were,
however, factors which aggravated the spread of the virus, including
bird migration, cool temperature (increases virus survival) and several
festivals at that time.
A mutation in the virus was discovered in two Guangdong patients
in February 2017 which rendered it more deadly to chickens, inasmuch as
it could infect every organ; the risk to humans was not increased,
however.
Controversial research
A
study published in 2012 in Science Magazine reported on research
findings that allowed for the airborne transmission of H5N1 in
laboratory ferrets. The study identified the 5 mutations necessary for
the virus to become airborne and immediately sparked controversy over
the ethical implications of making such potentially dangerous
information available to the general public. The study was allowed to
remain available in its entirety, though it remains a controversial
topic within the scientific community.
The study in question, however, created airborne H5N1 via amino
acid substitutions that largely mitigated the devastating effects of the
disease. This fact was underscored by the 0% fatality rate among the
ferrets infected via airborne transmission, as well as the fundamental
biology underlying the substitutions. Flu viruses attach to host cells
via the hemagluttinin proteins on their envelope. These hemagluttinin
proteins bind to sialic acid receptors on host cells, which can fall
into two categories. The sialic acid receptors can be either 2,3 or
2,6-linked, with the species of origin largely deciding receptor
preference. In influenzas of avian origin 2,3-linkage is preferred, vs.
influenzas of human origin in which 2,6-linkage is preferable.
2,3-linked SA receptors in humans are found predominantly in the lower
respiratory tract, a fact that is the primary foundation for the
deadliness of avian influenzas in humans, and also the key to their lack
of airborne transmission. In the study that created an airborne avian
influenza among ferrets it was necessary to switch the receptor
preference of the host cells to those of 2,6-linkage, found
predominantly in humans' upper respiratory tract, in order to create an
infection that could shed aerosolized virus particles. Such an
infection, however, must occur in the upper respiratory tract of humans,
thus fundamentally undercutting the fatal trajectory of the disease.
H7N9
Influenza A virus subtype H7N9 is a novel avian influenza virus first reported to have infected humans in 2013 in China. Most of the reported cases of human infection have resulted in severe respiratory illness.
In the month following the report of the first case, more than 100
people had been infected, an unusually high rate for a new infection; a
fifth of those patients had died, a fifth had recovered, and the rest
remained critically ill. The World Health Organization (WHO) has identified H7N9 as "...an unusually dangerous virus for humans." As of June 30, 133 cases have been reported, resulting in the deaths of 43.
Research regarding background and transmission is ongoing. It has been established that many of the human cases of H7N9 appear to have a link to live bird markets.
As of July 2013, there had been no evidence of sustained
human-to-human transmission, however a study group headed by one of the
world's leading experts on avian flu reported that several instances of
human-to-human infection were suspected.
It has been reported that H7N9 virus does not kill poultry, which will
make surveillance much more difficult. Researchers have commented on
the unusual prevalence of older males among H7N9-infected patients. While several environmental, behavioral, and biological explanations for this pattern have been proposed, as yet, the reason is unknown. Currently no vaccine exists, but the use of influenza antiviral drugs known as neuraminidase inhibitors in cases of early infection may be effective.
The number of cases detected after April fell abruptly. The
decrease in the number of new human H7N9 cases may have resulted from
containment measures taken by Chinese authorities, including closing
live bird markets, or from a change in seasons, or possibly a
combination of both factors. Studies indicate that avian influenza
viruses have a seasonal pattern, thus it is thought that infections may
pick up again when the weather turns cooler in China.
In the four years from early 2013 to early 2017, 916 lab-confirmed human cases of H7N9 were reported to WHO.
On 9 January 2017, the National Health and Family Planning
Commission of China reported to WHO 106 cases which occurred from late
November through December. 29, 2016. The cases are reported from
Jiangsu (52), Zhejiang (21), Anhui (14), Guangdong (14), Shanghai (2),
Fujian (2) and Hunan (1). 80 of these 106 persons have visited live
poultry markets. Of these cases, there have been 35 deaths. In two of
the 106 cases, human-to-human transmission could not be ruled out.
Affected prefectures in Jiangsu province closed live poultry
markets in late December 2016, whereas Zhejiang, Guangdong and Anhui
provinces went the route of strengthening live poultry market
regulations. Travellers to affected regions are recommended to avoid
poultry farms, live bird markets, and surfaces which appear to be
contaminated with poultry feces. Similar sudden increases in the number
of human cases of H7N9 have occurred in previous years during December
and January.
Domestic animals
A chicken being tested for flu
Several domestic species have been infected with and shown symptoms
of H5N1 viral infection, including cats, dogs, ferrets, pigs, and birds.
Birds
Attempts
are made in the United States to minimize the presence of HPAI in
poultry through routine surveillance of poultry flocks in commercial
poultry operations. Detection of a HPAI virus may result in immediate
culling of the flock. Less pathogenic viruses are controlled by
vaccination, which is done primarily in turkey flocks (ATCvet codes: QI01AA23 (WHO) for the inactivated fowl vaccine, QI01CL01 (WHO) for the inactivated turkey combination vaccine).
Cats
Avian influenza in cats
can show a variety of symptoms and usually lead to death. Cats are able
to get infected by either consuming an infected bird or by contracting
the virus from another infected cat.
Global impact
In 2005, the formation of the International Partnership on Avian and Pandemic Influenza
was announced in order to elevate the importance of avian flu,
coordinate efforts, and improve disease reporting and surveillance in
order to better respond to future pandemics. New networks of
laboratories have emerged to detect and respond to avian flu, such as
the Crisis Management Center for Animal Health, the Global Avian
Influenza Network for Surveillance, OFFLU,
and the Global Early Warning System for major animal diseases. After
the 2003 outbreak, WHO member states have also recognized the need for
more transparent and equitable sharing of vaccines and other benefits
from these networks.
Cooperative measures created in response to HPAI have served as a basis
for programs related to other emerging and re-emerging infectious
diseases.
HPAI control has also been used for political ends. In Indonesia,
negotiations with global response networks were used to recentralize
power and funding to the Ministry of Health. In Vietnam policymakers, with the support of the Food and Agriculture Organization of the United Nations (FAO),
used HPAI control to accelerate the industrialization of livestock
production for export by proposing to increase the portion of
large-scale commercial farms and reducing the number of poultry keepers
from 8 to 2 million by 2010.
Stigma
Backyard
poultry production was viewed as "traditional Asian" agricultural
practices that contrasted with modern commercial poultry production and
seen as a threat to biosecurity. Backyard production appeared to hold
greater risk than commercial production due to lack of biosecurity and
close contact with humans, though HPAI spread in intensively raised
flocks was greater due to high density rearing and genetic homogeneity.
Asian culture itself was blamed as the reason why certain
interventions, such as those that only looked at placed-based
interventions, would fail without looking for a multifaceted solutions.
Indonesia
Press
accounts of avian flu in Indonesia were seen by poultry farmers as
conflating suspected cases while the public did see the accounts as
informative, though many became de-sensitized to the idea of impending
danger or only temporarily changed their poultry-related behavior. Rumors also circulated in Java
in 2006. These tended to focus on bird flu being linked to big
businesses in order to drive small farmers out of the market by
exaggerating the danger of avian influenza, avian flu being introduced
by foreigners to force Indonesians to purchase imported chicken and keep
Indonesian chicken off the world market, and the government using avian
flu as a ploy to attract funds from wealthy countries. Such rumors
reflected concerns about big businesses, globalization, and a distrust
of the national government in a country where "the amount of
decentralization here is breathtaking" according to Steven Bjorge, a WHO
epidemiologist in Jakarta in 2006.
In the context a decentralized national government that the
public did not completely trust, Indonesian Health Minister Siti Fadilah
Supari announced in December 2006 that her government would no longer
be sharing samples of H5N1 collected from Indonesian patients. This
decision came as a shock to the international community as it disrupted
the Global Influenza Surveillance Network (GISN) coordinated by the WHO
for managing seasonal and pandemic influenza. GISN is based on countries
sharing virus specimens freely with the WHO which assesses and
eventually sends these samples to pharmaceutical companies in order to
produce vaccines that are sold back to these countries.
Though this was initially seen as an attempt to protect national
sovereignty at all costs, it was instead used for a domestic political
struggle. Prior to Indonesia's dispute with the GISN, the Ministry of
Health, already weak due to the decentralized nature the government, was
experiencing further leakage of funding to state and non-state agencies
due to global health interventions. By reasserting control over public
health issues and funding by setting itself up as the sole Indonesian
representative to the WHO, the Ministry of Health made itself a key
player in the management of future international funds relating vaccine
production and renegotiated benefits from global surveillance networks.
Economic
Approximately 20% of the protein consumed in developing countries come from poultry.
In the wake of the H5N1 pandemic, millions of poultry were killed. In
Vietnam alone, over 50 million domestic birds were killed due to HPAI
infection and control attempts. A 2005 report by the FAO totaled economic losses in South East Asia around US$10 billion.
This had the greatest impact on small scale commercial and backyard
producers relative to total assets compared to industrial chains which
primarily experience temporary decreases in exports and loss of consumer
confidence. Some governments did provide compensation for culled
poultry, it was often far below market value (close to 30% of market
value in Vietnam), while others such as Cambodia provide no compensation
to farmers at all.
As poultry serves as a source of food security and liquid assets, the most vulnerable populations were poor small scale farmers.
The loss of birds due to HPAI and culling in Vietnam led to an average
loss of 2.3 months of production and US$69–108 for households where many
have an income of $2 a day or less. The loss of food security for vulnerable households can be seen in the stunting of children under 5 in Egypt. Women are another population at risk as in most regions of the world, small flocks are tended to by women. Widespread culling also resulted in the decreased enrollment of girls in school in Turkey.
Prevention
People
who do not regularly come into contact with birds are not at high risk
for contracting avian influenza. Those at high risk include poultry farm
workers, animal control workers, wildlife biologists, and
ornithologists who handle live birds.
Organizations with high-risk workers should have an avian influenza
response plan in place before any cases have been discovered.
Biosecurity of poultry flocks is also important for prevention. Flocks
should be isolated from outside birds, especially wild birds, and their
waste; vehicles used around the flock should be regularly disinfected
and not shared between farms; and birds from slaughter channels should
not be returned to the farm.
With proper infection control and use of personal protective equipment
(PPE), the chance for infection is low. Protecting the eyes, nose,
mouth, and hands is important for prevention because these are the most
common ways for the virus to enter the body. Appropriate personal
protective equipment includes aprons or coveralls, gloves, boots or boot
covers, and a head cover or hair cover. Disposable PPE is recommended.
An N-95 respirator and unvented/indirectly vented safety goggles are also part of appropriate PPE. A powered air purifying respirator (PAPR) with hood or helmet and face shield is also an option.
Proper reporting of an isolated case can help to prevent spread. The Centers for Disease Control and Prevention
(US) recommendation is that if a worker develops symptoms within 10
days of working with infected poultry or potentially contaminated
materials, they should seek care and notify their employer, who should
notify public health officials.
For future avian influenza threats, the WHO suggests a 3 phase, 5 part plan.
- Phase: Pre-pandemic
- Reduce opportunities for human infection
- Strengthen the early warning system
- Phase: Emergence of a pandemic virus
- Contain or delay spread at the source
- Phase: Pandemic declared and spreading internationally
- Reduce morbidity, mortality, and social disruption
- Conduct research to guide response measures
Vaccines for poultry have been formulated against several of the
avian H5N1 influenza varieties. Control measures for HPAI encourage mass
vaccinations of poultry though The World Health Organization has
compiled a list of known clinical trials of pandemic influenza prototype
vaccines, including those against H5N1.
In some countries still at high risk for HPAI spread, there is
compulsory strategic vaccination though vaccine supply shortages remain a
problem.
For village poultry farmers
During
the initial response to H5N1, a one size fits all recommendation was
used for all poultry production systems, though measures for intensively raised birds were not necessarily appropriate for extensively
raised birds. When looking at village-raised poultry, it was first
assumed that the household was the unit and that flocks did not make
contact with other flocks, though more effective measures came into use
when the epidemiological unit was the village.
Recommendations involve restructuring commercial markets to
improve biosecurity against avian influenza. Poultry production zoning
is used to limit poultry farming to specific areas outside of urban
environments while live poultry markets improve biosecurity by limiting
the number of traders holding licenses and subjecting producers and
traders to more stringent inspections. These recommendations in
combination with requirements to fence and house all poultry, and to
limit free ranging flocks, will eventually lead to fewer small
commercial producers and backyard producers, costing livelihoods as they
are unable to meet the conditions needed to participate.
A summary of reports to the World Organisation for Animal Health in 2005 and 2010 suggest that surveillance and under-reporting in developed and developing countries is still a challenge. Often, donor support can focus on HPAI control alone, while similar diseases such as Newcastle disease, acute fowl cholera, infectious laryngotracheitis, and infectious bursal disease still affect poultry populations. When HPAI tests come back negative, a lack of funded testing for differential diagnoses can leave farmers wondering what killed their birds.
Since traditional production systems require little investment
and serve as a safety net for lower income households, prevention and
treatment can be seen as less cost-effective than letting poultry die.
Effective control not only requires prior agreements to be made with
relevant government agencies, such as seen with Indonesia, they must
also not unduly threaten food security.
Culling
The interior of a barn showing infected birds who have been killed by suffocation with foam.
Culling is used in order to decrease the threat of avian influenza transmission by killing potentially infected birds. The FAO
manual on HPAI control recommends a zoning strategy which begins with
the identification of an infected area (IA) where sick or dead birds
have tested positive. All poultry in this zone are culled while the area
1 to 5 km from the outer boundary of the IA is considered the
restricted area (RA) placed under strict surveillance. 2 to 10 km from
the RA is the control area (CA) that serves as a buffer zone in case of
spread. Culling is not recommended beyond the IA unless there is
evidence of spread.
The manual, however, also provides examples of how control was carried
out between 2004 and 2005 to contain H5N1 where all poultry was to be
stamped out in a 3 km radius beyond the infected point and beyond that a
5 km radius where all fowl was to be vaccinated. This culling method
was indiscriminate as a large proportion of the poultry inside these
areas were small backyard flocks which did not travel great enough
distances to carry infection to adjacent villages without human effort
and may have not been infected at all. Between 2004 and 2005, over 100 million chickens were culled in Asia to contain H5N1.
The risk of mass culling of birds and the resulting economic
impact led to farmers who were reluctant to report sick poultry. The
culls often preempted actual lab testing for H5N1 as avian flu policy
justified sacrificing poultry as a safeguard against HPAI spread.
In response to these policies, farmers in Vietnam between 2003 and 2004
became more and more unwilling to surrender apparently healthy birds to
authorities and stole poultry destined for culls as it stripped poultry
of their biosocial and economic worth. By the end of 2005, the
government implemented a new policy that targeted high-risk flock in the
immediate vicinity of infected farms and instituted voluntary culling
with compensation in the case of a local outbreak.
Not only did culling result in severe economic impacts especially
for small scale farmers, culling itself may be an ineffective
preventative measure. In the short-term, mass culling achieves its goals
of limiting the immediate spread of HPAI, it has been found to impede
the evolution of host resistance which is important for the long-term
success of HPAI control. Mass culling also selects for elevated
influenza virulence and results in the greater mortality of birds overall.
Effective culling strategies must be selective as well as considerate
of economic impacts to optimize epidemiological control and minimize
economic and agricultural destruction.
People-poultry relations
Prevention
and control programs must take into account local understandings of
people-poultry relations. In the past, programs that have focused on
singular, place-based understandings of disease transmission have been
ineffective. In the case of Northern Vietnam, health workers saw poultry
as commodities with an environment that was under the control of
people. Poultry existed in the context of farms, markets,
slaughterhouses, and roads while humans were indirectly the primary
transmitters of avian flu, placing the burden of disease control on
people. However, farmers saw their free ranging poultry in an
environment dominated by nonhuman forces that they could not exert
control over. There were a host of nonhuman actors such as wild birds
and weather patterns whose relationships with the poultry fostered the
disease and absolved farmers of complete responsibility for disease
control.
Attempts at singular, place-based controls sought to teach
farmers to identify areas where their behavior could change without
looking at poultry behaviors. Behavior recommendations by Vietnam's
National Steering Committee for Avian Influenza Control and Prevention
(NSCAI) were drawn from the FAO Principles of Biosecurity.
These included restrictions from entering areas where poultry are kept
by erecting barriers to segregate poultry from non-human contact, limits
on human movement of poultry and poultry-related products ideally to
transporters, and recommendations for farmers to wash hands and footwear
before and after contact with poultry.
Farmers, pointed to wind and environmental pollution as reasons poultry
would get sick. NSCAI recommendations also would disrupt longstanding
livestock production practices as gates impede sales by restricting
assessment of birds by appearance and offend customers by limiting
outside human contact. Instead of incorporating local knowledge into
recommendations, cultural barriers were used as scapegoats for failed
interventions. Prevention and control methods have been more effective
when also considering the social, political, and ecological agents in
play.
