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| The Threat of Pandemic Influenza: Are We Ready? Workshop Summary
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OCR for page 222
The Threat of
Pandemic Influenza: Are We Ready? - Workshop Summary 4 Strategies for
Controlling Avian Influenza in Birds and Mammals OVERVIEW To address
the threat that avian influenza (AI) poses to human health, it is
necessary to recognize its broader agricultural and economic
implications and to integrate this knowledge into disease control
strategies. This chapter focuses on the global phenomenon of avian
influenza, its impact on the poultry industry, and potential means to
control influenza transmission among birds and mammals. The chapter
begins with a review of the activities of the Office International des
Épizooties (OIE; also known as the World Organisation for Animal
Health), an international and intergovernmental organization at the
forefront of animal disease control. The OIE is developing influenza
surveillance guidelines that encompass birds, domestic mammals,
wildlife, and humans. The OIE recently initiated cooperation between
its global network of reference laboratories and that of the World
Health Organization (WHO); the partners plan to exchange scientific
information on avian influenza, share viral isolates, and may
eventually manufacture human vaccines against avian viral strains.
While avian influenza is an uncommon disease of poultry in the United
States, the U.S. Department of Agriculture (USDA) recognizes the
international importance of the disease and has developed considerable
animal health policies to detect, prevent, and control avian influenza.
These strategies are presented, along with background information on
the biology, ecology, and epidemiology of avian influenza, by David
Swayne and David Suarez of the USDA. They review evidence that supports
intervention and
OCR for page 223
The Threat of
Pandemic Influenza: Are We Ready? - Workshop Summary surveillance
focused on the subset of avian influenza viruses that pose significant
risk of infecting humans, including certain viruses of low
pathogenicity in poultry. The chapter concludes with an example of a
low-pathogen avian influenza outbreak in a group of commercial poultry
farms and the steps the industry took to contain further spread of the
virus, minimize the risk of exposure, and monitor and prevent further
infections. STANDARDS AND ACTIVITIES OF THE OIE RELATED TO AVIAN
INFLUENZA Dewan Sibartie Scientific and Technical Department World
Organisation for Animal Health (OIE) Introduction Preventing the spread
of animal diseases and zoonoses through international trade is one of
the primary objectives of the World Organisation for Animal Health
(OIE). This is accomplished by establishing international standards
that facilitate trade while minimizing the risk of introducing
infectious animal diseases and zoonoses. The OIE was founded in 1924,
as a result of an outbreak of rinderpest in Belgium. Initially 28
countries united with a mandate to share information on animal disease
outbreaks to allow the Member Countries to take the appropriate control
measures to protect themselves and to prevent further spread of the
disease. A total of 167 countries now form part of the OIE, and
providing a mechanism for prompt reporting of disease outbreaks and
occurrences is still one of the OIE’s primary roles. Over the years,
the OIE has been strongly committed to convincing national policy
makers and international donors that the cost of strengthening
veterinary services to provide better surveillance, early warning
systems, and management of epizootics, including zoonoses, is
negligible compared to the economic losses resulting from introduction
of infectious animal diseases and zoonoses. The OIE objectives and
activities for the prevention and control of infectious animal diseases
and zoonoses are focused on the following areas: Transparency in animal
disease status worldwide Each Member Country is committed to reporting
to the OIE on its health status regarding significant animal diseases
and diseases transmissible to humans. The OIE then disseminates the
informa-
OCR for page 224
The Threat of
Pandemic Influenza: Are We Ready? - Workshop Summary tion to all Member
Countries to enable them to take appropriate actions to protect
themselves. Collection, analysis, and dissemination of veterinary
information Using its network of internationally recognized scientists,
the OIE collects, analyzes, and publishes the latest scientific
information on important animal diseases, including those transmissible
to humans, especially regarding their prevention and control.
Strengthening of international coordination and cooperation in the
control of animal diseases The OIE provides technical expertise to
Member Countries requesting assistance with animal disease control and
eradication programs, particularly in developing countries. These
activities are performed in coordination with other international
organizations responsible for supporting and funding the eradication of
infectious animal diseases and zoonoses. Promotion of the safety of
world trade in animals and animal products The OIE develops standards
for application by Member Countries to protect themselves against
disease incursions as a result of trade in animals and animal products,
while avoiding unjustified sanitary barriers. These standards are
developed by experts from Member Countries and from the OIE’s network
of more than 160 Collaborating Centers and Reference Laboratories. In
1995 the standards developed by the OIE were formalized as
international standards by the Agreement on the Application of Sanitary
and Phytosanitary Measures (SPS Agreement) of the World Trade
Organization (World Trade Organization, 1995). In order to harmonize
SPS measures and remove unjustifiable sanitary or health restrictions
on international trade, the Agreement states that governments should
follow these international standards, guidelines, and recommendations.
The goal of the Agreement is to minimize the risk of disease
transmission and remove unjustifiable sanitary or health restrictions
on international trade. The Agreement states that it is the sovereign
right of a country to provide an appropriate level of animal and public
health protection at its borders. However, this sovereign right is not
to be misused for protectionist purposes: An importing country can only
apply sanitary measures to imports if a similar level of protection is
applied to all imports and internally by the importing country. Member
Countries can introduce standards providing a higher level of
protection than that provided by the OIE standards if there is a
scientific justification, but these standards must be based on a
science-based risk analysis. The OIE recognizes highly pathogenic avian
influenza (HPAI) as an
OCR for page 225
The Threat of
Pandemic Influenza: Are We Ready? - Workshop Summary OIE list A1
disease having the potential for very serious and rapid spread,
irrespective of national borders, which can be of serious socioeconomic
and public health consequences and which is of major importance to the
international trade of poultry and poultry products. Since 1996 it has
become clear that avian influenza viruses may be important pathogens
capable of infecting humans directly without reassortment. This has
been observed during the recent outbreaks of AI in southeast Asia.
However, like other organizations also concerned with human health, the
OIE is highly concerned about the possibility that the virus can
undergo genetic reassortment and become transmissible within humans,
resulting in a pandemic capable of claiming millions of lives, as was
the case during the so-called Spanish flu of 1918. Firmly convinced
that the best way to reduce human exposure to the virus is to eliminate
the virus at source—that is, from animals, including wild birds—the OIE
strives to assist Member Countries in providing expertise particularly
in the following areas: disease surveillance, early detection, early
warning and notification, quality and evaluation of veterinary
services, diagnosis, surveillance, control strategies, and
international trade in poultry and poultry products. OIE Reference
Laboratories and Experts The OIE is coordinating a worldwide network of
some 150 Reference Laboratories and 13 Collaborating Centers and more
than 300 experts in various animal diseases. For avian influenza, there
are currently six Reference Laboratories and eight experts, but the OIE
also benefits from the expertise of other internationally renowned
scientists in the field of AI who are called on to assist OIE ad hoc
groups or to carry out technical missions on behalf of the OIE in
countries affected by the disease. The OIE Reference Laboratories
played a particularly significant role during the avian influenza
outbreaks in southeast Asia caused by H5NI strain of the AI virus. Not
only have the experts of those laboratories provided technical advice,
but they have, for example, also provided useful diagnostic material
such as H5 antigens to laboratories in affected countries to assist
them in their diagnosis. The application of the Differentiating
Infected from Vaccinated Animals (DIVA) tests developed by the OIE
Reference Laboratory in Italy will be particularly useful for countries
that will embark on the use of marker vaccines for the control of AI.
The OIE Reference Laboratories also conduct training courses for
technical staff in the diagnosis of the disease and characterization of
the virus. In addition, the OIE Reference Laborato- 1
Diseases to be urgently notified by Member Countries.
OCR for page 226
The Threat of
Pandemic Influenza: Are We Ready? - Workshop Summary ries are arranging
cooperation with the network of the WHO Influenza Reference
Laboratories for the exchange of scientific information, sharing of
viruses for strain characterizations, and if necessary, the manufacture
of human vaccines from poultry strains of the virus. OIE Standards One
of the major activities of the OIE is to develop standards, guidelines,
and recommendations for the diagnosis and control of important animal
diseases, including zoonoses. OIE standards are science-based and are
developed by experts and approved by the OIE International Committee,
which has representatives from the 167 Member Countries. The World
Trade Organization Agreement on Sanitary and Phyto-Sanitary (WTO-SPS)
measures recognizes the OIE as the only international organization for
setting standards on animal diseases and zoonoses. Standards concerning
terrestrial (nonaquatic) animals are contained in the Terrestrial
Animal Health Code (the Terrestrial Code) (World Organisation for
Animal Health, 2003) and the OIE Manual of Diagnostic Tests and
Vaccines, or Terrestrial Manual (World Organisation for Animal Health,
2004a). The Terrestrial Code provides the governments and the Chief
Veterinary Officers of OIE Member Countries with recommendations for
establishing national health measures or rules applicable to the
importation of animals and animal products with respect to OIE listed
animal diseases in order to avoid importation of pathogens while
avoiding unjustified sanitary barriers. The Terrestrial Manual
describes the diagnostic methods that are to be used and the methods
for the production and control of biological products, including
vaccines. The Terrestrial Code Definition of avian influenza infection.
Chapter 2.1.14 of the Terrestrial Code provides standards for highly
pathogenic avian influenza (HPAI). However, in view of the latest
scientific advances, especially regarding the potential risks posed by
low-pathogenic strains and the ability of the virus to infect humans, a
new Chapter (World Organisation for Animal Health, 2004b) has been
proposed by an OIE ad hoc group of experts and is being studied by OIE
Member Countries. A new definition of notifiable avian influenza has
been proposed as follows: For the purposes of this Terrestrial Code,
notifiable avian influenza (NAI) is defined as an infection of poultry
caused by any influenza A virus of the H5 or H7 subtypes or by any AI
virus with an intravenous pathogenicity index (IVPI) greater than 1.2
(or as an alternative at least 75 percent mortality) as described
below. NAI viruses can be divided into highly
OCR for page 227
The Threat of
Pandemic Influenza: Are We Ready? - Workshop Summary pathogenic
notifiable avian influenza (HPNAI) and low-pathogenicity notifiable
avian influenza (LPNAI): 1. HPNAI viruses have an IVPI in 6-week-old
chickens greater than 1.2 or, as an alternative, cause at least 75
percent mortality in 4- to 8-week-old chickens infected intravenously.
H5 and H7 viruses, which do not have an IVPI of greater than 1.2 or
cause less than 75 percent mortality in an intravenous lethality test,
should be sequenced to determine whether multiple basic amino acids are
present at the cleavage site of the hemagglutinin molecule (HA); if the
amino acid motif is similar to that observed for other HPNAI isolates,
the isolate being tested should be considered as HPNAI. 2. LPNAI are
all influenza A viruses of H5 and H7 subtypes that are not HPNAI
viruses. Disease notification. The current Terrestrial Code provides
for countries to report HPAI within 24 hours. If the proposed Chapter
is approved, countries would start notifying all NAI as defined above.
Countries also need to report a provisional diagnosis of HPAI if this
represents important new information of epidemiological significance to
other countries. The OIE in turn forwards this information to other
countries in order for countries at risk to take appropriate
precautions. Following outbreaks of AI in southeast Asia, the OIE
collaborated with other international organizations to provide
expertise to countries in the region to improve their disease reporting
systems. Thanks to the “rumours tracking system,” the OIE has been able
to query some countries about rumours of the possible occurrence of AI
in those countries. This system proved effective in that at least two
countries that had not reported the disease to the OIE then confirmed
the presence of the disease. In view of the zoonotic importance of the
disease, the OIE is working in close collaboration with WHO on the
notification of all important zoonoses. As a result there is constant
and instant sharing of information between the two organizations about
the occurrence of AI in animals and humans. Evaluation of veterinary
services. The Terrestrial Code provides guidelines for the quality and
the evaluation of veterinary services (which include public and private
components) in Member Countries. This is important to assert the
credibility of the services because it enhances the international
acceptance of the certification of exports and facilitates the risk
analysis process of an importing country. The results of this
evaluation can help provide the importing country the assurance that
information on sanitary/ zoosanitary situations provided by the
veterinary services of an exporting country is objective, meaningful,
and correct. Evaluation of veterinary services has gained further
importance since the ban on imports of poultry and poultry products
from several southeast Asian countries following the avian
OCR for page 228
The Threat of
Pandemic Influenza: Are We Ready? - Workshop Summary influenza crisis.
For countries to resume their trade, especially with Europe, the
veterinary services must demonstrate efficiency in terms of diagnosis,
surveillance, and certification for exports. The Terrestrial Code
spells out the procedures for an independent and reliable certification
free from political or other commercial considerations. International
trade of poultry and poultry products. As mentioned earlier, the OIE
provides standards, guidelines and recommendations to assure the
sanitary safety of international trade in animals and animal products
to avoid the transfer of agents pathogenic for animals or humans while
avoiding unjustified sanitary barriers. In this context, the OIE is
fully aware of the constraints faced by countries wishing, for example,
to export fresh poultry meat. These constraints relate mainly to
vaccination, surveillance, and zoning/compartmentalization. The new
proposed Chapter attempts to solve some of these constraints,
especially in the light of the outbreaks in southeast Asia, Europe, and
North America. During a meeting of AI experts jointly organized by the
Food and Agriculture Organization of the United Nations (FAO), the OIE,
and WHO, held in February 2004 in Bangkok, Thailand, the three
organizations agreed that due to ethical, social, economic, and
environmental reasons, the stamping-out policy may not be appropriate
for some countries in the region. Thus they recommended that
vaccination, which has proved to reduce morbidity, mortality, and virus
shedding, can provide an additional useful tool in those countries
provided that the vaccines used comply with the standards of the OIE
Terrestrial Manual and that vaccines are administered under the
supervision of the official veterinary services. The veterinary
services should have the necessary expertise and resources to ensure
that appropiate and adequate surveillance is carried out to avoid
possible problems caused by vaccination, the main one being the
difficulty in differentiating infected from vaccinated animals by
serology. The proposed Code Chapter allows the export of live birds
from countries, zones, or compartments that have been vaccinated
provided details of the vaccines and the vaccination programs are
stated. In order to assist well-managed enterprises with a high level
of biosecurity to export, the Chapter proposes that the concept of
compartmentalization be adopted. The Code defines
“compartmentalization” as “one or more establishments under a common
biosecurity management system containing an animal subpopulation with a
distinct health status with respect to a specific disease for which
required surveillance, control, and biosecurity measures have been
applied for the purpose of international trade.” This concept will
enable countries having integrated and well-managed poultry enterprises
to export under certain conditions even if the rest of the country is
infected. The new Chapter also proposes that a country or
zone/compartment
OCR for page 229
The Threat of
Pandemic Influenza: Are We Ready? - Workshop Summary may be considered
free from NAI when it has been shown that NAI infection has not been
present for the past 12 months. If infected poultry are slaughtered,
this period shall be 3 months (instead of 6) after the slaughter of the
last infected poultry and disinfection of all affected premises. This
would encourage countries wishing to resume exports to carry out
stamping-out whenever feasible and apply strict biosecurity measures.
The OIE has already put at the disposal of Member Countries relevant
expertise to help them improve the production and quality control of
vaccines. Such help is also available for the establishment of OIE
Reference Laboratories on AI. Surveillance and monitoring of animal
health. The Terrestrial Code has a generic chapter outlining the
general requirements for a country to carry out surveillance and
monitoring of animal health. The fundamental principles described in
that Chapter also apply to avian influenza. However, an OIE ad hoc
group of experts will soon be working on a specific Chapter on
surveillance guidelines for avian influenza, taking on board the latest
scientific knowledge on AI. In the meantime the new proposed Chapter on
AI spells out certain general ideas on serological surveillance in
flocks, especially in the presence of vaccination. The DIVA tests
developed by an OIE Reference Laboratory will prove helpful to
countries using marker vaccines. The principle of this test is accepted
by the OIE, and further work on its applicability to other animal
diseases is in progress in some OIE Reference Laboratories. Information
provided by the exporting country’s surveillance and monitoring program
is considered to be a key component of the risk analysis conducted by
an importing country. OIE has provided and will continue to provide
expert assistance to southeast Asian countries to improve surveillance
and monitoring systems to control the disease. The OIE advises that
countries establish programs to monitor high-risk avian populations,
such as live bird markets, fighting cocks, and other markets selling
wild birds. This should decrease the risk of AI transmission through
trade. The Terrestrial Code also provides detailed procedures for
conducting a risk analysis that also applies to AI. Member Countries
are allowed under the WTO-SPS Agreement to apply a higher level of SPS
measures provided there is a scientific justification and it is
supported by a risk analysis. The Terrestrial Manual The Terrestrial
Manual is a companion volume to the Terrestrial Code and provides a
uniform approach to the diagnosis of HPAI. Its purpose is also to
facilitate international trade in animals and animal products by
describing internationally agreed-on laboratory methods for avian
influ-
OCR for page 230
The Threat of
Pandemic Influenza: Are We Ready? - Workshop Summary enza diagnosis and
requirements for the production and quality control of AI vaccines. The
methods described also form the basis for effective avian influenza
surveillance and monitoring. The serological techniques described
include the hemagglutination-inhibition and agar gel immunodiffusion
tests. The immunodiffusion test is a group-specific test that can
detect all strains of avian influenza virus and is appropriate for a
monitoring program. The Chapter also mentions the use of commercial
Enzyme Linked Immunosorbent Assay (ELISA) kits that detect antibody
against the nucleocapsid protein. Such tests have usually been
evaluated and validated by the manufacturer, and it is essential that
the manufacturer’s instructions be followed. Although not specifically
mentioned in the Chapter on HPAI, the importance of marker vaccines and
the DIVA test are well recognized by the OIE. Virus isolation
techniques and virus characterization techniques for the confirmation
of HPAI are also described in detail. Stamping-Out and Carcass Disposal
The OIE continues to rely on the principle that stamping-out remains
the method of choice for the rapid elimination of the virus and thus
its spread to humans, but is fully aware that this method is not
applicable to certain countries for reasons stated earlier. For this
reason, the OIE has an ad hoc group that has formulated recommendations
for the mass slaughter of animals during an emergency and the safe
disposal of carcasses. These methods vary depending on the available
resources, equipment, and infrastructure. Work is progressing by an OIE
ad hoc group on carcass disposal, and the OIE will finalize details of
the methods applicable in different situations. Food Safety In
pursuance with one of its missions to ensure safety of food of animal
origin, OIE experts have conducted research on the possible
contamination of humans through the consumption of poultry meat or
products. This has been particularly important during the recent
influenza outbreaks in southeast Asia, when consumption of these
commodities fell drastically, threatening millions of farmers who
depend almost entirely on subsistence animal farming for their
livelihoods. Therefore it was important to restore consumer confidence
in poultry products. OIE experts have concluded that humans can only be
infected while in contact with infected birds and that the main mode of
transmission in humans in the context of this Asian epizootic is by the
respiratory route. In addition, they have demonstrated that when
poultry products are cooked to an internal temperature of at least
70°C, the virus is destroyed.
OCR for page 231
The Threat of
Pandemic Influenza: Are We Ready? - Workshop Summary The Role of
Wildlife The role of wildlife in the transmission and spread of AI has
been widely discussed by the international scientific community. In a
February 2004 meeting, the OIE experts in the Working Group on Wildlife
Diseases reviewed the available literature and other relevant
documentation and made the following salient observations: Virtually
all H and N combinations have been isolated from birds. Wild birds,
particularly those associated with aquatic environments, are the
reservoirs of viruses of low virulence for poultry. Viruses may become
virulent following transmission and cycling in commercial poultry.
There is current concern about the lack of knowledge on the prevalence
of viruses of H5 and H7 subtypes in bird populations. Outbreaks of
disease in commercial poultry have been linked to a close association
between commercial poultry and waterfowl on many occasions. Isolation
of virus from other wild birds is completely overshadowed by the
number, variety, and distribution of influenza viruses isolated from
waterfowl. The highest rate of detection of influenza virus is from
ducks. The concentration of ducks, their potential to excrete high
levels of virus and its ability to remain viable in an aquatic
environment means that “large” areas of the environment will be
contaminated. Different virus subtypes can be identified simultaneously
within a single bird. The predominant subtype isolated from domestic
ducks varies from year to year. Natural protection of ducks does not
provide cross-protection between influenza A subtypes. Influenza
viruses can sweep through bird populations without having any signs of
disease present. Studies indicate that the viruses identified in
Eurasia and Australia are genetically distinct from those in North
America. This most likely reflects the distinct flyways of each
hemisphere. There is an “avian influenza season” (at least in temperate
countries) in the fall/winter. Surveillance programs of wild birds when
outbreaks of poultry influenza have occurred often find little or no
signs of infection. Therefore, they recommend that as far as
practically possible, wild birds should be separated from commercial
poultry. Surveillance programs
OCR for page 232
The Threat of
Pandemic Influenza: Are We Ready? - Workshop Summary should also be
conducted in wild birds, placing more emphasis on ducks and using
sentinel birds to detect presence of the disease; in temperate zones,
surveying should be concentrated in young birds in the fall/winter.
They also emphasized that surveillance is of global interest because
this type of information in one country is important for other
countries to know. However, the Working Group is of the unanimous
opinion that the role of wild birds in occurrences of virulent
influenza A in poultry and in humans is widely misunderstood. Virulent
strains of these viruses seldom have been found in wild birds, even in
association with outbreaks in poultry. The Working Group does not
contest the possibility that the co-cycling of more than one influenza
strain within a so-called “mixing vessel” host such as the pig may
result in genetic exchanges and genetic shift. Such events could result
in the evolution of highly pathogenic viral strains with rapid
passaging and spread, especially within and between intensively farmed
poultry houses, and with high risk of “cross-over” infection to humans.
Control programs for virulent strains of avian influenza viruses
therefore should be focused on biosecurity of poultry populations and
protection of humans exposed to poultry. Continual OIE Involvement The
OIE continues to monitor the worldwide AI situation closely, paying
particular attention to southeast Asia, where the disease has far more
economic and possibly more public health impact. Relevant information
is posted continuously on the OIE website (http://www.oie.int) to
update Member Countries on the prevailing situation. On March 19, 2004,
the OIE again alerted countries on the unjustified optimism being
displayed by certain countries on the perception that the epidemic is
over. The OIE has appealed to Member Countries to maintain vigilance
because the virus is still circulating and eradication is a long way
ahead. This has been proven to be true as outbreaks of highly
pathogenic avian influenza have again been recently recorded in some
countries of southeast Asia that thought they had successfully overcome
the outbreaks. Since January 27, 2004, the OIE has been alerting
international donors about the pressing need to provide assistance to
countries in southeast Asia affected by the disease. Assistance also
should be provided to strengthen veterinary services and to improve
surveillance and early response to diseases. There cannot be any delay
in this assistance not only because of economic reasons, but because no
opportunity should be given to that virus to undergo genetic
reassortment in human beings and thus create a new human influenza
pandemic.
OCR for page 243
The Threat of
Pandemic Influenza: Are We Ready? - Workshop Summary cant veterinary
diagnostic and regulatory infrastructure improvements are needed in the
developing world to accomplish this goal. These aspects in a global
control strategy are lacking in most developing countries, especially
Asia. This inability to detect and eliminate AI infections prior to
human infections and reassortment are the real threats that may lead to
the next world pandemic. LOW-PATHOGENICITY AVIAN INFLUENZA OUTBREAKS IN
COMMERCIAL POULTRY IN CALIFORNIA Carol Cardona, DVM, PhD, dipl. ACPV
University of California, Davis Outbreak of H6N2 Avian Influenza in
California California has experienced a number of outbreaks of avian
influenza in commercial poultry over the years. Most of these outbreaks
have been in turkeys and have previously been reported (Ghazikhanian et
al., 1981; McCapes et al., 1986). Beginning in 2000, an outbreak of
H6N2 avian influenza began in commercial egg-laying chickens in
southern California (Webby et al., 2003; Woolcock et al., 2003).
Initially, the infecting virus caused no disease or clinical signs;
however, by 2001, the virus seemed to be more adapted to growth in
chickens in that it seemed to spread more easily, and was associated
with decreased egg production and decreased egg quality in infected
flocks (Kinde et al., 2003). The outbreak expanded to new areas of the
state and to new types of poultry over a period of 2 years. Because the
strain of this virus was not H5 and not H7, there were no regulations
or plans in place to control this virus. Eventually, the poultry
industry of California was able to control this outbreak with a
voluntary plan they developed, but it was not before a great deal of
damage had been done. The H6N2 low-pathogenicity strain of avian
influenza virus, which infected commercial poultry in California, is
not a strain regulated by either the California Department of Food and
Agriculture (CDFA) or the USDA. Most American trading partners and,
therefore, regulatory agencies, focus on H5 and H7 viruses. This is
completely understandable because these are the viruses that may mutate
to become highly pathogenic strains (Easterday et al., 1997). After our
experience in California, we believe that low-pathogenicity strains of
all types can cause significant losses for commercial poultry
producers. And the same connections between farms that would spread an
H5 or an H7 strain would also result in the spread of a virus of any H
or N type. Although state and federal regulatory agencies have
OCR for page 244
The Threat of
Pandemic Influenza: Are We Ready? - Workshop Summary focused on
specific viruses for a very good reason, this is a rather arbitrary
decision and one that has limited the study of the AI viruses that are
the most prevalent among avian species. The Spread of AIV Among
Commercial Poultry Farms Commercial poultry companies are first and
foremost businesses. They are streamlined to reduce production and
processing costs, while maximizing profit margins. Many of the
practices involved in the modern production of poultry also support the
spread and amplification of disease agents such as AI virus. In
California’s experience with avian influenza, one such practice was the
movement of eggs from the farm to the processing plant. Eggs are
collected from the flocks that produced them, then brought to
processing plants, where they are cleaned and packed for stores. This
proved to be an important way in which avian influenza was transmitted
from farm to farm. Eggs are packed on reusable flats in the chicken
house. Those flats are then placed onto pallets or racks, which go to
the processing plant. Most eggs that are packed are clean, but some may
be contaminated by fecal material. That fecal material is often
transferred to the reusable plastic flats, where it becomes mixed with
other organic material such as broken eggs. The reusable flats are
emptied at the plant, washed (less than perfectly), returned to pallets
or racks, and then returned either to the farm they came from or to
another unrelated farm. When flats and racks are sent to different
farms, they carry infectious material from their farm of origin,
resulting in the spread of disease. We suspect that AI virus spread
among many egg-laying farms by this means. Other practices that
probably played a part in the spread of AI virus in California include
moving live birds to slaughter; moving manure off infected farms;
rendering pickups of dead birds; sharing equipment; and using common
transporters and service crews. These practices alone are not unsafe
and would not be suspect if farms were distant from each other, but
they were not. Poultry farms, like many other types of animal
agriculture, are frequently located near each other to take advantage
of shared resources. These resources include feed mills, rendering
plants, slaughter facilities, and markets. The result has been that in
parts of California, Georgia, Arkansas, Iowa, North Carolina, and other
states with large poultry industries, there are local regions with
dense populations of poultry. These dense populations, if infected with
AI virus, can serve to exponentially expand the virus in a relatively
small region, resulting in the infection of both commercial and
noncommercial poultry. Concentrations of commercial poultry support the
growth of population sectors, which in turn support animal agriculture.
The large numbers
OCR for page 245
The Threat of
Pandemic Influenza: Are We Ready? - Workshop Summary of low-paying,
low-skill positions in animal agriculture often attract new immigrants
as workers. These new immigrants are frequently also engaged in
activities that involve live birds, such as cockfighting and the
purchase of birds for food at live bird markets. The former has been
implicated in the spread of the exotic Newcastle disease virus in
California and the latter has been implicated in the spread and
maintenance of H7N2 avian influenza virus in the northeastern United
States (Bulaga et al., 2003). Both of these populations, the game fowl
and the birds produced for live bird markets, have the potential to
become reservoirs of virus for commercial poultry populations.
Unfortunately, in California and in other parts of the country, neither
of these populations is surveyed regularly for disease, and few markets
utilize veterinary services. The Control of Low-Pathogenicity Avian
Influenza in California Once the commercial companies involved in the
California outbreak realized they could not economically live with this
virus, they developed a voluntary control plan that required
surveillance and biosecurity, and placed limits on the movements of
infected flocks. The first part of the plan required participants to
minimize the risk of exposure with the following biosecurity practices:
Transportation of birds Minimize the movement of birds Use on-site
composting or cremation if possible to dispose of carcasses after
euthanasia Move birds safely, if they must be moved Avoid driving near
other poultry facilities Test flocks 2 weeks prior to movement Birds
with clinical disease should never be moved Clean, disinfected trucks
should be used Principles of biosecurity should be closely followed
Move infected birds only to slaughter Actively shedding birds should
not be moved to another facility Previously infected birds are strongly
discouraged from movement except to slaughter Movement of manure Manure
trucks must be tarped before they leave any facility They must follow
routes that avoid contact with other poultry traffic
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The Threat of
Pandemic Influenza: Are We Ready? - Workshop Summary Multiple pickups
from different farms on the same day are not allowed Manure should be
pushed to the edge of the property for pickup Traffic patterns should
be established that avoid interaction between manure trucks and other
farm traffic Scheduling should be done to avoid clean traffic Manure
should not be spread or stored close to any other poultry Marketing of
eggs Dedicated racks and flats will be used for each ranch Racks and
flats from different ranches will not be commingled Flats will be
washed and disinfected at the processing plant Rack washing at the
processing plant is strongly encouraged Feed mills and feed delivery
Feed trucks should be cleaned and disinfected at the feed mill They
should be kept away from “clean” areas of the production facility They
should be cleaned and disinfected again when they enter a facility
Drivers should be either kept away from “clean” areas or provided with
protective clothing All trucks and equipment leaving a facility should
be cleaned and disinfected before exiting the facility if suspect or
positive flocks are present Movement of crews A representative of the
poultry company will monitor all work performed by crews to ensure that
the following rules are observed: Protective clothing and footwear
provided by the ranch must be worn Hand washing is required before
handling birds Crew vehicles should be cleaned and disinfected before
they enter a facility or, preferably, they should be left off site
Mortality disposal Onsite cremation or composting are the preferred
methods of mortality disposal Use renderers safely, if they must be
used Tarp trucks Put mortality pickup at the edge of the property
Coordinate the routing of the truck to avoid “clean” farm traffic
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The Threat of
Pandemic Influenza: Are We Ready? - Workshop Summary Shared employees
Employees should not be shared by poultry companies Employees are
required to wear clean clothes to work Employees are required to
disinfect their footwear before entering production facilities Clean
rooms for changing and clean clothes should be provided for employees
Shower facilities are optimal, but are not required Shared equipment
Equipment should not be shared between poultry facilities If it is
shared, it should be cleaned and disinfected at both ends Physical
proximity Communicate with neighbors to avoid behaviors that endanger
each other’s flocks Control vectors (rodents and insects) as much as
possible Communication of disease status between neighbors is required
Common vendors (propane, utility, supplies, etc.) Keep unnecessary
visitors off the farm Visitors should wear protective clothing to enter
the facility A consistent visitor policy should be established for all
premises Keep a logbook of visitors The producer participants in the
plan were also required to Monitor for new infections with the
following surveillance of their flocks: When there is little risk of
infection, flocks will be tested at slaughter During times when there
is a risk of infection: 20 birds will be tested for AI by AGID monthly
Flocks must be checked daily for: Decreases in egg production Increased
mortality Clinical signs of disease The next critical step is to
determine what should happen with a positive flock. Because there was
no money for the indemnification of their losses, depopulation of the
flocks was not considered an option. However, the producers selected
another strategy, controlled marketing, which has been highly
successful in controlling AI in turkeys in Minnesota (Halvorson
OCR for page 248
The Threat of
Pandemic Influenza: Are We Ready? - Workshop Summary et al., 1986). The
California plan required the following to Control the virus—making a
responsible response to AI virus infection: Negative flocks (never
infected with avian influenza virus) have no restrictions on movement
Virus-negative flocks (previously positive but no longer shedding
virus): Move to slaughter Pullets (young hens) may be moved to a
positive lay ranch Suspect flocks Get a diagnosis as soon as possible
Contact your veterinarian, and/or Submit birds to the diagnostic
laboratory Notify your neighbors Self-quarantine Positive flocks
(currently infected and shedding avian influenza virus) Notify
neighboring poultry farms Self-quarantine Do not move birds until the
flock is no longer shedding virus Coordinate movement of the flock to
minimize risk Document route and time of travel and let other producers
know or Euthanize and dispose of the flock on site (composting or
cremation) Limit exposure of carcasses to predators and other
mechanical vectors The final step in the California control plan is how
to Prevent infection in future flocks. In this step, the California
producers relied heavily on the use of a killed autogenous vaccine. The
use of vaccine allowed them to stop the cycle of infection in multi-age
farms, which have a continuous flow of new birds entering the infected
farm. Vaccination was highly successful for most farms, but only when
implemented in conjunction with biosecurity practices. Clean and
disinfect the farm Leave sufficient downtime before repopulation (at
least 2 weeks)
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The Threat of
Pandemic Influenza: Are We Ready? - Workshop Summary Use of vaccine in
flocks at risk of infection Fulfill all CDFA/USDA requirements for
biosecurity and flock plans Using this voluntary plan, California
controlled and eradicated H6N2 AI virus from commercial poultry flocks.
The producers in the state soon learned that not telling each other
about AI virus infections resulted in the spread of the outbreak. The
outbreak was stopped when more communication began among all types of
producers. This seems like a simple lesson to have learned, but the
poultry producers and processors in California are no different from
other small business owners in that they do not usually share
confidential information with their competitors. To achieve the level
of communication that resulted in the eradication of AI virus in
California, all participants had to agree not to use infection status
to gain a competitive advantage. Exposure of Humans to Poultry in the
United States The U.S. commercial poultry industry protects public
health by focusing its efforts on preventing poultry infections with AI
viruses. This goal of prevention is both economically rewarding for the
poultry business and a sound public health practice. However, because
natural AI virus reservoirs are widely dispersed, this strategy does
not always work, as was the case in California. When AI virus
infections occur, it is important to understand where and how the
general public interacts with poultry in order to assess and minimize
risk of spread. Many people envision poultry production as it was 100
years ago, as a dozen chickens on the family farm. However, today,
poultry production occurs on large farms that house dense populations
of chickens or turkeys. The industrialization of food production has
meant that the general public is not exposed to the processes by which
they are fed. The work force that produces all the food we need to
survive is small and in the case of poultry, includes workers in
poultry facilities and slaughterhouses, bird haulers, vaccination
crews, manure haulers, renderers, and veterinarians. These workers are
the most likely to be exposed to poultry pathogens infecting commercial
poultry flocks. In many parts of the world, poultry for consumption are
purchased live, allowing the consumer to assess the bird’s health and
fitness. Live bird markets also exist in the United States, on the east
coast, in the midwest, and in the major immigrant centers on the west
coast (Los Angeles and San Francisco). Live bird markets all over the
world are an important part of daily commerce and represent both a
mixing pot of avian and mammalian disease agents and a steady stream of
human traffic. The transmission of
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The Threat of
Pandemic Influenza: Are We Ready? - Workshop Summary avian influenza to
humans in Hong Kong in 1997 (Mounts et al., 1999; Shortridge et al.,
2000; Subbarao et al., 1998) and in other parts of Asia (Webster, 2004)
has raised the profile of live bird markets. Although surveillance has
been increased, disease control measures have been established in only
a few locations (Mullaney, 2003), primarily because they have been
difficult to conceive and implement. Today, in the United States and
all over the world, these markets remain a key location where the
public is in direct contact with poultry that are sometimes actively
shedding AI virus. Perhaps the most intensive contact between poultry
and people in the United States occurs among those individuals who own
poultry for hobby purposes or keep them as a continuing source of eggs
or fresh meat. These individuals come from a wide variety of cultural
backgrounds and socioeconomic strata. However, these
individuals—including cockfighters, 4H participants, poultry fanciers,
and backyard flock owners—have one thing in common: few of them take
their birds to veterinarians. This is partially due to a lack of
interest in poultry on the part of most practicing veterinarians and
partly because these owners do not want to spend money for veterinary
care. Because they rarely see veterinarians, AI virus infections in
these types of flocks usually go undetected and unreported. This lack
of care combined with the level of contact between flock owners and
hobby or backyard chickens make these human and poultry interactions
some of the most important to public health. So, while the general
public is largely limited in its exposure to poultry by intensive
farming and biosecurity practices, there are a number of exceptions
through which humans may be intensively exposed to poultry. These
scenarios are where disease prevention in poultry flocks is limited by
a lack of contact with veterinarians and a lack of poultry husbandry
knowledge that public health may be critically at risk. Unfortunately,
many of the people most intensively exposed to these small populations
of poultry are also underserved by human health professionals. In
California, the outbreak of H6N2 avian influenza in densely populated
poultry regions resulted in the exposure of many small flocks to AI
virus. How many were infected or their types are not known. However, we
suspect that some of these noncommercial flocks are now persistently
infected manmade reservoirs for the virus. These types of reservoirs
have been implicated in the spread of disease to commercial flocks, but
their roles in public health have been largely invisible. Conclusions
The fact that California’s low-pathogenicity strain of avian influenza
virus was of the H6N2 type did not prevent it from spreading to many
OCR for page 251
The Threat of
Pandemic Influenza: Are We Ready? - Workshop Summary commercial poultry
flocks or from causing disease and production losses in infected
chickens and turkeys. In addition, the fact that this virus was not of
the H5 or H7 types does not limit its potential to donate genetic
material to potential pandemic strains. The interaction of animal
agriculture and the public is complex and dynamic, and we do not fully
understand the risks associated with the various types of contacts
between humans and birds. We do not know where or how the next pandemic
influenza virus will arise, but that lack of knowledge should not limit
the surveillance we conduct in birds or in the public.
Low-pathogenicity strains of AI virus are the most prevalent strains
among all species of birds, including commercial poultry. Non-H5 and
-H7 low-pathogenicity AI viruses have contributed genetic material to
the highly pathogenic viruses currently circulating in Asia (Chin et
al., 2002), and one has infected humans (Lin et al., 2000). Our
knowledge of where the next pandemic virus will arise is too premature
to eliminate as irrelevant the non-H5 or -H7 avian influenza strains.
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Representative terms from entire chapter:
influenza viruses, commercial poultry, animal health, influenza virus, controlling avian, pandemic influenza, wild birds, animal diseases, live bird, veterinary services, terrestrial code, international trade, reference laboratories, turkey breeders, swine influenza, bird markets, highly pathogenic, hong kong, virus infections, live poultry, world organisation, oie reference, hpai viruses, influenza outbreaks, lpai viruses, control strategies, viruses isolated, pathogenic avian, drinking water, poultry products
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