Vulnerability Assessment Avian Influenza Introduction into Manitoba Domestic Poultry and Swine
By the Manitoba Agriculture, Food and Rural Initiatives - Influenza type A is a viral disease affecting many species of animals, including birds, pigs, people, horses, sea mammals, and most recently, dogs and cats. Influenza viruses are genetically unstable and mutations are common.
31 July 2006
12 minute read
Executive Summary
1.1 Clinical Disease in Animals
These
mutations may occur gradually or in some cases, dramatically, causing a shift in
the pathogenicity (disease-causing ability) or adaptation to a new host species. In
commercial poultry, the virus infects the respiratory and digestive tracts causing
respiratory distress (difficult breathing) and in severe cases, sudden death. In
commercial flocks infected with a highly pathogenic virus the death losses can be
dramatic.
In mammalian species, influenza affects primarily the respiratory tract but it can
spread to become a generalized systemic infection. In most cases, the infection
causes high rates of morbidity (clinical illness) but relatively low mortality.
However, when epidemics strike a susceptible population the mortality rates can
be significant. The present concern over the H5N1 Asian strain of avian
influenza virus is its demonstrated ability to cause illness and death in humans.
1.2 Risk from Wildlife - Evolution of Dangerous Strains
Many species of wild water birds can carry influenza viruses asymptomatically,
but young of the year mallard ducks seem to harbour the virus most consistently.
The classic route for an outbreak of highly pathogenic avian influenza in
domestic poultry occurs when a low pathogenic strain of the virus jumps from
wild waterfowl into dry land poultry, such as chickens or turkeys. The virus then
cycles undetected in commercial flocks until it mutates into in a highly pathogenic
strain that causes clinical illness.
Highly pathogenic strains commonly kill over 50% of the affected birds within 24
hours and are easily detected clinically. The length of time that low pathogenic
virus can circulate undetected within commercial poultry is unpredictable. To
date, the virus has become highly pathogenic only in large commercial flocks of
chickens, turkeys and other gallinaceous birds with a flock size exceeding 10,000
individuals. The virus has not been documented to mutate into the deadly form in
domesticated waterfowl or small poultry flocks.
Avian influenza virus shed in the feces of migratory waterfowl and shorebirds can
survive for extended periods in untreated pond water. Confined commercial
poultry and swine may be exposed to the virus if untreated water is drawn from
such sources. Chlorination greatly reduces or eliminates the risk of introduction
by that route.
1.3 Small Flocks
Small flocks are very unlikely to act as silent carriers of avian influenza. Winter in
Manitoba provides a natural down time in which farms with small flocks are either
depopulated, or the birds are housed indoors. Small flock owners wishing to
reduce the risk of avian influenza infecting their birds can arrange to market their
summer flocks prior to the beginning of the wild waterfowl migratory season.
Alternatively, producers can house their birds during this time, when the risk of
spread of avian influenza from wild waterfowl is highest. Small flocks in
Manitoba are a minor risk to humans and commercial poultry.
1.4 Outdoor Goose Production
Domestic geese are highly resistant to low pathogenic forms of avian influenza.
There is no evidence to date that the virus has ever mutated to the highly
pathogenic form within a goose flock. If domestic geese are exposed to a highly
pathogenic form, introduced from other poultry or wild waterfowl, some morbidity
may occur. The most likely result of an introduction of Asian H5N1 avian
influenza into a domestic goose flock would be a low level of sick and dead birds
and a limited amount of shed of the virus. Increased clinical surveillance could
be relied upon to detect suspicious outbreaks that should be investigated further.
Manitoba accounts for half of the commercial goose production in Canada. There
are no known methods to raise commercial geese indoors. Confinement housing
of ducks is possible and some Manitoba producers have raised small flocks of
ducks indoors. A ban on outdoor production would effectively eliminate
commercial goose production in Manitoba. Increased biosecurity
recommendations for geese would include protection of the feed and water
supplies from fecal contamination by wild birds, and fencing off ponds that are
frequented by wild migratory ducks and geese.
1.5 Turkey Production
Manitoba turkey flocks are at a high risk to be the entry point for any new
influenza virus. This is because many turkey flocks are allowed access to the
outdoors and because infected turkeys usually exhibit milder clinical symptoms,
compared to chickens. It should be noted that an exception to this pattern
occurred in Italy in 2001 when a turkey-adapted strain caused significant
mortality in commercial turkeys prior to mutating into a chicken pathogen.
Historically, although turkeys are far less populous than chickens, they are
disproportionately more likely to be identified in new outbreaks of highly
pathogenic avian influenza. Recently, Manitoba turkey breeding flocks have been
clinically affected by swine-adapted H3N2 influenza despite widespread
vaccination and high biosecurity protocols. Special attention should be paid to
increasing clinical surveillance of turkey flocks and investigating reports of
disease.
1.6 Chicken Production
Chicken production is segmented into meat and egg production, each with their
associated parent breeding stock. Commercial chicken meat flocks live less than
45 days under total confinement and unless influenza is introduced through a
breakdown in biosecurity, there is little opportunity for the disease to be
maintained in this type of production system. Table egg laying chickens are also
kept indoors under strict biosecurity protocols. However, these birds are longer
lived so that if low pathogenic influenza virus is introduced, there is more
opportunity for the virus to mutate into a highly pathogenic form. Highly
pathogenic avian influenza causes a dramatic drop in egg production; therefore,
normal egg production acts as a sensitive indicator of absence of infection. The
initial flocks infected in the British Columbia 2004 outbreak were flocks
maintained to nearly 2 years of age for the production of hatching eggs for the
chicken meat industry. Increased mortality and a dramatic drop in egg production
were the first signs of infection in these birds and the private veterinary
practitioner was called in promptly to investigate.
1.7 Influenza A in Swine
Influenza infection of pigs does have some potential human health implications,
although recent outbreaks of pig-adapted viruses have not been associated with
human deaths. The movement of low pathogenic avian strains or the H5N1 Asian
highly pathogenic strain of avian influenza from wild birds to pigs has not been
associated with high mortality in pig populations in Asia. However, if Asian strain
H5N1 were to be identified in the Manitoba swine complex, multiple
repercussions could be expected, especially if there was associated human
illness or death. These might include the closure of the US border to live swine
and pork, worker refusal to enter swine buildings, extreme logistic problems in
dealing with surplus animals and the public perception of danger.
1.8 Public Health
The current strain of Asian H5N1 virus transmits from poultry to people with
difficulty and only under specific exposure conditions of very close contact. The
human-poultry interaction in Manitoba is significantly different from that in other
countries where poultry, pigs and people live in very close proximity. With the
same land mass as Thailand, Manitoba has 1/60th the human population, 1/30th
the number of poultry and 1/1000th the number of flocks; therefore, the
opportunity for transmission between poultry and humans is extremely low.
For the general public, the most noticeable impact of the emergence of Asian
H5N1 avian influenza may be public alarm in relation to the very visible numbers
of Canada Geese and other wild water birds in urban settings. If these birds are
not displaying clinical signs, the risk to humans is likely to be very small.
Nevertheless, it is prudent to use normal hygienic practices when exposed to wild
birds or their droppings. Pets (such as dogs and cats) may be exposed to the
virus if they swim in drainage ponds or if they hunt and consume sick birds.
Strategically, human-adapted influenza viruses currently circulating in swine are
of a higher potential public health risk than are North American strains of
waterfowl-associated avian influenza. Increased surveillance and investigation of
respiratory disease outbreaks in swine might provide an early warning of
influenza circulating within that population.
The present human health concern is rightly focused on the biological stability of
the current epizootic strain of Asian H5N1. Should this virus become adapted to
humans then all agricultural-based risks would become irrelevant.
1.9 Recommendations
Surveillance
In cooperation with producers, veterinary practitioners and federal animal health partners, enhance the surveillance and field investigation capacity of the Provincial Veterinary Services. This would target investigations into clinical illnesses of commercial and backyard poultry flocks. The CVO of Manitoba is lead on the surveillance component of the federal-provincial Canadian Animal Health Surveillance Network. This affords the opportunity to pilot a novel surveillance system in Manitoba.
Working with producers and their veterinarians, initiate a disease surveillance program specifically targeted to outdoor goose and outdoor turkey production.
Work cooperatively with wildlife officials to actively investigate suspicious clinical disease and mortality in wild migratory birds.
Enhance laboratory surge capacity in viral diagnosis in veterinary services, especially for early detection of influenza viruses.
Encourage laboratory sample submissions from commercial and backyard poultry flocks as a method of monitoring poultry diseases. Response
Implement provincial legislative and regulatory changes to permit the registry of food processing animals, especially commercial and backyard flocks, and swine operations.
Work with producer organizations, the Manitoba Veterinary Medical Association, provincial and federal agencies to refine and test emergency disease response plans involving the poultry and swine industries.
Put in place the necessary response tools such as GIS mapping, Incident Command Structures, and Emergency Operations Centres to deal with animal health emergencies.
Educate small flock owners to either market the birds before the start of the “fall bird migration season” or to keep their birds from contact with migratory waterfowl during this period. Education and voluntary compliance are likely to be highly effective given the intense public interest in the matter.
Prevent domestic waterfowl and poultry from accessing open water frequented by migratory waterfowl.
Guard water and feed sources for domestic poultry and swine from fecal contamination from wild birds. Chlorinate water drawn from ponds and dugouts.
Separate domestic species. Wherever possible, raise only one species of poultry on a farm, and do not raise poultry where swine are housed.
On farms where multiple species are kept, implement and enforce strict biosecurity practices between barns. Encourage commercial producers to enroll in on-farm food safety (quality assurance) programs.
Promote rapid reporting and investigation of suspicious illness in domestic poultry and swine.
Promote public education to emphasize prudent hygienic practices when in contact with waterfowl or their droppings, especially during the fall migration. Prevent pets from contacting or consuming dead or sick birds.
Work cooperatively with producers, veterinary practitioners and other provincial and federal agencies to prepare for an influenza outbreak in poultry, pigs or people. Through the federal-provincial Canadian Animal Health Surveillance Network cooperate with other provinces and CFIA to increase surveillance and diagnostic capacity for influenza in all species.
Avian influenza (H5N1 southeast Asian strain) has spread throughout Asia into Europe and Africa, probably through the migration of wild waterfowl and shorebirds. It is very likely that this strain will spread to North America by the same route.
This strain of virus has demonstrated a high degree of pathogenicity in domestic poultry and, to a lesser degree, in its natural host, migratory waterfowl. Over 90 people who have had very close contact with infected poultry have died worldwide, but it is unknown how many hundreds of thousands, or even millions have been exposed to the virus and have not developed any clinical illness.
The risk of such close contact in Manitoba is very small indeed. Our commercial flock production practices are very different from those in southeast Asia and our producers implement biosecurity measures to protect domestic poultry from coming into contact with wild birds. On those farms that keep birds outdoors (geese and turkeys), extra precautions to protect feed and water supplies, and to fence off ponds will greatly reduce the opportunity for spread of the virus from wild to domestic birds. Although swine have not yet been reported to be a significant part of the epidemiology of the disease, they remain as a potentially vulnerable sector in Manitoba. Similar biosecurity measures are recommended as a wise precaution in swine herds.
Contents
SECTION 1 – EXECUTIVE SUMMARY
1.1 Clinical Disease in Animals
1.2 Risk from Wildlife - Evolution of Dangerous Strains
1.3 Small Flocks
1.4 Outdoor Goose Production
1.5 Turkey Production
1.6 Chicken Production
1.7 Influenza A in Swine
1.8 Public Health
1.9 Recommendations
1.10 Conclusion
SECTION 2 - INTRODUCTION
2.1 Summary Points
2.2 Infectious Agent
2.3 Historic Summary
SECTION 3 - THE MANITOBA SITUATION
3.1 Summary Points
3.2 Comparison of Manitoba Poultry Production to British Columbia
3.3 Poultry Demographics in Manitoba
3.4 Comparison of Manitoba Poultry Production to Thailand
3.5 Wild Duck and Goose Demographics in Manitoba
SECTION 4 - UNDERSTANDING AND COMMUNICATING RISKS
4.1 Summary Points
4.2 Risk Analysis
SECTION 5 - RISK PATHWAY 1 CLASSICAL PATHWAY OF INTRODUCTION
OF INFLUENZA-A
5.1 Summary
5.2 Evidence
SECTION 6 - RISK PATHWAY 1C WILD BIRDS TO DOMESTIC GEESE
6.2 Summary
6.2 Evidence
SECTION 7 - ROUTE 2 INTRODUCTION OF ZOONOTIC AVIAN INFLUENZA
FROM ASIA
7.1 Summary
7.2 Evidence
7.3 Current International Scientific Recommendations Asian H5N1*
SECTION 8 - ROUTE 3 RISK OF AI MOVEMENT THROUGH PIGS
8.1 Summary
8.2 Evidence
SECTION 9 - ROUTE 4 LIVE BIRD MARKET INVOLVEMENT
9.1 Summary
9.2 Evidence
SECTION 10 - ROUTE 5 RISK OF AI MOVEMENT FROM PIGS TO POULTRY
10.1 Summary
10.2 Evidence
SECTION 11 - MOST SIGNIFICANT RISK TO MANITOBA AGRICULTURE
11.1 Risk to Small Flocks
11.2 Risk to Swine Production
11.3 Risk to Poultry from Swine Production
SECTION 12 - MOST SIGNIFICANT RISK TO PUBLIC HEALTH
12.1 Summary
12.2 Evidence
SECTION 13 - REFERENCES
Further Information
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April 2006
