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Outbreak Investigation Report on H5N2 Avian Influenza in Ontario, 2015

Table of Contents

List of Acronyms

AEOC

Area Emergency Operations Centre

AHFP

Animal Health Functional Plan

AICZ

Avian Influenza Control Zone

BHT

Biological Heat Treatment

C&D

Cleaning and disinfection

CanNAISS

Canadian Notifiable Avian Influenza Surveillance System

CFIA

Canadian Food Inspection Agency

CVO

Chief Veterinary Officer

CWHC

Canadian Wildlife Health Cooperative

DBS

Dead Bird Surveillance

EOC

Emergency Operations Centre

FADES

Foreign Animal Disease Emergency Support (Plan)

FBCC

Feather Board Command Center

GIS

Geographic Information System

HPAI

Highly Pathogenic Avian Influenza

HSP

Hazard Specific Plan

ICS

Incident Command System

IP

Infected Premises

NAI

Notifiable Avian Influenza

NCFAD

National Centre for Foreign Animal Diseases

NEOC

National Emergency Operations Centre

WOAH

World Organization for Animal Health (founded as Office International des Épizooties (OIE))

OMAFRA

Ontario Ministry of Agriculture, Food and Rural Affairs

PHAC

Public Health Agency of Canada

PIQ

Premises Investigation Questionnaire

PPE

Personal Protective Equipment

REOC

Regional Emergency Operations Centre

TAHC

Terrestrial Animal Health Code

Report Objective

This report describes the 2015 outbreak and response to highly-pathogenic H5N2 avian influenza (HPAI) in Oxford County, Ontario, Canada. In describing the Canadian Food Inspection Agency's (CFIA) implementation of disease control measures, this report demonstrates to the Canadian public and external stakeholders that Canada has met all obligations described in current World Organisation for Animal Health (WOAH) guidelines.

Summary

  • HPAI was identified in a meat turkey farm on April 5th, 2015. Subsequently, two other commercial farms were infected with the same virus: one broiler breeder and one turkey genetics. All birds on infected premises were humanely destroyed and composted on-site.
  • The virus was identified as an H5N2, a reassortant virus with the H5 from the highly pathogenic Eurasian H5N8 virus and the N2 from a North American virus.
  • Movement restrictions were placed on 73 farms in two clusters: 31 were located within 10 km of Infected Premises (IP) 1 and 42 were located within 10 km of IPs 2 and 3. Movement restrictions were also placed on two premises outside of these clusters due to significant contact with an IP.
  • The CFIA undertook a complete outbreak investigation, including an epidemiological analysis. It was determined that:
    • For two infected farms, the source of the virus was contact with wild birds.
    • For one infected farm, the source of the virus is suspected to be localized/environmental spread.
  • Surveillance was completed on 70 commercial farms from April 14th, 2015 to July 27th, 2015 with over 1,300 samples collected testing negative for HPAI virus.
  • Post-outbreak surveillance was completed during the period from July 8th, 2015 through October 8th, 2015 with 160 samples tested in 160 premises, with negative results.

1. Oxford County of Ontario - Outbreak Context

1.1 Geography and Climate

Oxford County is located in southwest Ontario, and includes the city of Woodstock. The area has a significant amount of agriculture and is fairly diverse in terms of the sectors represented. Southwest Ontario has significant populations of wild resident and migratory waterfowl. Oxford County lies within the Mississippi Flyway (Figure 1), which extends East-West from Saskatchewan to Quebec and North-South from the Arctic to the Gulf of Mexico and the Caribbean.

The weather station in Woodstock reported a transition month with 35 cm of snow on the ground and temperatures as low as -21°C on March 4th warming to a high of 9.5°C and all snow melted by March 20th.  This rapid melting resulted in localized flood conditions, exacerbated by temperatures dropping to below freezing overnight. Similar weather patterns to this have been associated with driving rodents and wild birds into barns, potentially resulting in increased disease spread.

Figure 1 – The Mississippi Flyway

The Mississippi Flyway. Description follows.
Description for Figure 1 - The Mississippi Flyway (Texas Parks and Wildlife Department)

This map shows the south to north path of the Mississippi Flyway through North America. Ontario is on the flyway.

The bird migration route generally follows the Mississippi River in the United States and the Mackenzie River in Canada. The main end points are North-Central Canada and the region surrounding the Gulf of Mexico.

1.2 Structure of the Poultry Industry

The commercial poultry industry in Ontario is highly integrated. Each sector is represented by a separate organization, and there are marketing boards for chicken meat, turkey meat, table eggs, and hatching eggs. These groups work together to address biosecurity issues and motivate producers to cooperate with disease surveillance and control programs. Outside the supply-managed sectors, smaller sectors include layer breeders, turkey breeders, ducks, geese, squab, pheasant, quail, and specialty chickens.

The non-commercial poultry sector in Ontario is diverse and individual production systems are unique. There is no mandatory registry for the non-commercial poultry sector.

The poultry industry in Ontario represents approximately 52% of the total Canadian poultry sector. In Ontario, 56% of the sector is composed of broilers, 12% are turkey producers, and hatching and table eggs do another 31%. There are 33 CFIA-registered hatcheries in Ontario, representing 33% of the national total.

1.3 Biosecurity

The CFIA, the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA), the Feather Board Command Center (FBCC) and respective industry groups have made an active effort to encourage good biosecurity practices in Ontario. These organizations, as well as CFIA, have also made emergency preparedness activities a priority.

2. National Avian Influenza Surveillance

2.1 Commercial Poultry

The Canadian Notifiable Avian Influenza Surveillance System (CanNAISS) is a joint initiative of government and industry that supports Canada's claim of freedom from NAI by providing ongoing surveillance of the commercial poultry population. The System is intended to prevent, detect and/or demonstrate the freedom from NAI in Canada's domestic poultry flocks. Designed to meet WOAH guidelines, CanNAISS pertains specifically to high-pathogenic avian influenza and low-pathogenic H5 and H7 subtypes of NAI. During an outbreak of NAI, CanNAISS provides surveillance on premises and areas not part of the outbreak, complementing the CFIA's NAI Hazard Specific Plan (HSP) and supporting Canada's reporting to international organizations such as the WOAH.

The CanNAISS includes:

  • Detection of HPAI in domestic poultry through passive surveillance;
  • Verification of the effectiveness of passive surveillance through active surveillance;
  • Detection of LPAI circulating in domestic poultry through active surveillance; and
  • Detection of NAI in post-outbreak surveillance.

2.2 Wild Birds

In 2005, Canada initiated an inter-agency annual survey for influenza A viruses in wild birds. These surveys (2005-2015) are used to assess the risk of exposure of AI from migrating wild birds to poultry. Since 2005, 4376 dead birds and 2794 live birds have been tested in Ontario under the Canadian Wildlife Health Cooperative (CWHC) national surveillance program. The Influenza A virus has been found in 686 samples including three positive samples for H5 (2005, 2007, 2010). 

3. Overview of Outbreak

3.1 Initial Detection

On April 3rd, 2015, samples from IP1 were sent by a private veterinary practitioner to the provincial Animal Health Laboratory (ALH) in Guelph, Ontario. The veterinarian had been called to the farm following a pattern (first noticed on April 1st, 2015) of increasing mortality in one barn, which contained the oldest birds. On April 5th, 2015, the AHL reported the detection of an H5 NAI in the submitted samples. Samples were then sent to the CFIA National Centre for Foreign Animal Diseases (NCFAD) in Winnipeg, Manitoba, which confirmed the virus was H5N2 on April 8th, 2015.

3.2 Findings on Infected Premises 1

The first infected premises (IP1) is a meat turkey operation located near Woodstock, Ontario. The operation is composed of four barns with birds at multiple stages of production, from 6.5 to 16.5 weeks of age. Each barn was initially stocked with 10,000 to 12,000 birds, all of which were around six weeks of age and obtained from a nearby brooder farm. All birds from this operation went directly to slaughter and all birds were obtained from the same brooder farm.

As noted previously, the premises contained four barns. Increasing mortality was noted in the first barn (B1), with approximately 4,500 birds remaining out of 9,900 birds initially placed. Birds in barns 2, 3 and 4 were 14.5, 8.5 and 6.5 weeks of age, respectively, with no significant mortalities.

Following a detailed epidemiological investigation, one high-risk premises was identified. This premises was the brooder barn that provided turkeys for IP1. The manager of this farm was a relative of the managers on IP1 and also assisted on the property as needed. As a result, this farm was placed under quarantine and monitoring for 21 days (three viral incubation periods) following the last contact between the premises. No evidence of infection was detected during this period.

The likely source of infection for this premises was a breach in biosecurity. CFIA staff on site reported significant numbers of small rodents within the barns as well as at least seven wild birds observed in one of the barns following destruction. Additionally, there were reports of wild waterfowl on the property in the weeks preceding infection.

3.3 Findings on Infected Premises 2

IP2 was a broiler breeder farm approximately 38 km from IP1 and was therefore outside the 10-km control zone.  Following a pattern of increasing mortality in one barn, samples were initially submitted to AHL by a private veterinary practitioner on April 17, 2015 and the subsequent H5 detection was reported to CFIA on April 18, 2015. H5N2 was confirmed by CFIA National Centre for Foreign Animal Disease (NCFAD) on April 19, 2015. 

The farm consisted of two connected barns with 12,000 to 13,000 birds per barn.  A ratio of 90% hens to 10% roosters was maintained, and all birds were approximately 29 weeks of age.

Following a detailed epidemiological investigation, no linkages between IP1 and IP2 were identified.

It is believed that this farm was also infected via a breach in biosecurity, b the evidence for this is not as strong as for IP1. In addition to farm management, five employees were active on this farm. All were interviewed and reported good biosecurity practices (boot wash / clothing change).  Some wild birds were observed on a compost pile located between the barns, but there were no reports of rodents or wild birds in the barns, so they cannot be confirmed as the source of infection.

The private veterinary practitioner who initially took samples for submission had performed initial post-mortem diagnostics in his clinic. This clinic was placed under quarantine until appropriate cleaning and disinfection could be verified. Also placed under quarantine were two broiler flocks visited by the veterinarian subsequent to the post mortem. The quarantine on these birds was lifted following negative diagnostic sampling.

3.4 Findings on Infected Premises 3

On April 23rd, 2015 CFIA was contacted by a turkey breeder operation with high relative mortality in one barn. Samples were collected and taken to AHL by CFIA staff and a resulting H5 positive was reported on the same day. H5N2 confirmatory results were reported by CFIA NCFAD on April 25, 2015. IP3 is located in close proximity to IP2, with an estimated 600 meters separating the closest barns.

This farm was composed of approximately 8,000 breeding turkeys located in four barns. Barns 1 and 2 were located near the road, and barns 3 and 4 were set approximately 400 meters further back.  Due to the nature of production, birds of different ages were maintained in the barns.

Given the nature and value of the birds located on IP3, and the inability of a genetics facility to make use of an all-in, all-out production cycle, an extremely stringent biosecurity protocol was described. A relatively large number (approximately 20) of staff were present on this site, all of whom were solely employed on this site.

The most likely source of infection for this premises was windborne transmission from IP2. As noted previously, the distance between the two properties was approximately 600 m. Contemporaneous records from nearby weather stations (in London and Woodstock, Ontario) indicated a strong wind in a south-easterly direction, supporting of a direct wind connection between IP2 and IP3, an observation shared by CFIA staff on IP2 on April 18, 2015 (five days prior to onset of clinical signs on IP3). This connection is further supported by the pattern of infection observed, wherein birds in the barn closest to IP2 were the first to show clinical signs. Further analysis from the CFIA NCFAD laboratory confirmed a higher degree of homology between the virus detected at IP2 and IP3 than between either site and IP1, though all strains were highly homologous with only minor variation between the locations thought to be due to random mutation. A breach in biosecurity is a less likely source of infection on this farm due to the stringent biosecurity protocol for this premises and its temporal and geographical proximity to IP2.

3.5 Laboratory Findings

Sequencing of the H5N2 virus obtained from samples of poultry on infected farms and analysis of the results indicated that it was a reassortant virus. The genome of all Influenza A viruses contains eight RNA gene segments, including hemagglutinin (H) and neuraminidase (N) genes, of which the H is the main gene segment involved in determining the pathogenicity. Based on sequence analysis, avian influenza viruses can be broadly categorized into Eurasian (Europe and Asia) and North American lineages. The new H5N2 virus detected in BC contains five of eight gene segments from highly pathogenic Eurasian H5N8 virus, including the H5 gene, and three of eight segments from typical North American viruses, including the N2 gene (originating in wild birds). It was the first time a Eurasian HPAI H5 lineage virus had been a cause of outbreaks of avian influenza in domestic poultry in North America. In addition, it appears that this particular reassortant virus with Eurasian and North American avian influenza virus gene segments had not been observed anywhere before, although all eight gene segments have been identified in either Asia/Europe or North America.

3.6 Outbreak Conclusion and Post-Outbreak Surveillance

Following destruction of the birds on each IP, carcasses, products and by-products were composted on site to deactivate the virus via bio-heat treatment (BHT). This was followed by cleaning and disinfection of the barns, then a 21-day fallow period. Cleaning and disinfection was approved for IP1 and IP3 on June 29th, 2015 and for IP2 on July 8th, 2015. The post-outbreak surveillance period started on July 8th, 2015 and concluded on October 8th, 2015.

4. Disease Control Actions

4.1 Response Infrastructure

4.1.1 The Role of the Canadian Food Inspection Agency

Notifiable avian influenza (NAI) virus is defined by the WOAH as any "type A" avian influenza virus with high pathogenicity, as well as all H5 and H7 virus subtypes. NAI is a federally reportable disease in Canada under the Health of Animals Act. The CFIA is the lead agency whenever a reportable animal disease is detected. Supportive roles are provided by other federal, provincial and municipal agencies, veterinary associations, and producer organizations.

4.1.2 The CFIA's Foreign Animal Disease Plans

The CFIA has developed strategies and operational plans to deal with potential incursions of foreign animal and reportable diseases. The Foreign Animal Disease Emergency Support (FADES) plan is the framework of federal-provincial cooperative agreements specifying their roles and responsibilities during an animal disease emergency. The FADES plan also describes the incident management system used to manage this outbreak.

The Notifiable Avian Influenza Hazard Specific Plan (NAI-HSP) forms part of the overall plan to deal specifically with an incursion of NAI; it supplies background information on the disease itself, as well as outlines the principles of disease control and eradication, premises disinfection, and surveillance. The emergency response structure and the procedures to implement these plans are set out in the CFIA Emergency Response Plan and the CFIA Animal Health Functional Plan (AHFP).

4.1.3 Emergency Operations Centres Established

When a high-risk specimen is submitted due to evidence of a federally-reportable disease, CFIA area and national emergency response teams are alerted. Once the diagnosis is confirmed, a sequence of events is activated that put in place the control and eradication procedures described in the NAI-HSP, the AHFP, and the CFIA Emergency Response Plan. At the discretion of the Area Director General, a regional and/or area emergency operations centre (REOC/AEOC) is established to coordinate the field investigation and disease control activities. In addition, a national EOC (NEOC) is established at Headquarters in Ottawa to support the field activities.

4.1.4 Area Emergency Operations Centre

The CFIA AEOC was activated on April 6, 2015, with the sections mobilizing in London, Ontario and Guelph, Ontario.

Support was provided by OMAFRA, who assisted with technical support and expertise, and who maintained a liaison role with CFIA throughout the response. Some OMAFRA staff were also embedded into the ICS structure as required. Additional support was provided by the FBCC who helped coordination with the poultry industry and provided industry specific knowledge and support as needed.

4.1.5 National Emergency Operations Centre

On April 6, 2015, the NEOC was activated in Ottawa. The NEOC provides support to the field activities associated with disease control and eradication policy, legal issues, communications, consultations with national producer groups, international relations, and inter-provincial liaison activities.

4.2 Establishment of Zones

In accordance with CFIA's NAI-HSP, all farms within 10 km containing susceptible species were placed under quarantine. Due to the close proximity between IP2 and IP3, all susceptible farms within 10 km of one were also within 10 km of the other, so a combined zone was created. For clarity, these zones were identified as Avian Influenza Control Zone (AICZ) 1 which surrounded IP1 and AICZ 2, surrounding IP2 and IP3.

4.3 Epidemiological Tracing

In accordance with CFIA's NAI-HSP and the WOAH's Terrestrial Animal Health Code (2014), the CFIA undertook movement tracing of all poultry, poultry products, and things exposed to poultry or poultry products associated with an infected premises during the 21-day period prior to the onset of clinical signs of NAI. This 21-day period, also known as the critical period, represents three times the maximum incubation period for avian influenza (7 days as cited by the WOAH). The date of an IP's first clinical signs was determined by examining production records and interviewing producers.

Based on information received from the laboratory indicating a high degree of homology between the 2015 Ontario NAI strain and the 2014 BC NAI strain, a decision was made in Ontario to shorten the incubation period from seven days to five. Even with this shorter incubation period, the 21-day critical period was maintained in response to this outbreak.

The purpose of epidemiological tracing is to:

  • Identify premises at risk of having been exposed to NAI virus by either direct or indirect contact with an infected premises; and
  • Identify potential sources of introduction of NAI virus to infected premises.

The CFIA's Premises Investigation Questionnaire (PIQ) was used to collect relevant epidemiological data on investigated poultry farms. Within the critical period, all direct movements of poultry on and off an IP were investigated and evaluated, considering the stage in the outbreak and level of risk. Trace-in (onto premises) and trace-out (off of premises) farms with no confirmed direct contact were subjected to a qualitative risk assessment to determine the potential for transmission by indirect contact. This indirect movement was classified as low, moderate, or high risk. Decisions concerning the traced premises were made by the Planning Chief with input from the National, and Area Planning Sections.

As of July 22nd, 2015, 26 traces were identified and completed. Of the 26 identified traces, three were related to movement of live birds, eight were related to service providers having contact with birds; seven were related to movements of products/by-products and eight were related to service providers having no contacts with birds.

4.4 Laboratory Investigation

The AHL (Animal Health Lab) in Guelph, ON is a Canadian Animal Health Surveillance Network (CAHSN) laboratory and conducted testing of all field samples for Matrix RRT-PCR for influenza A and RRT-PCR for H5.  The NCFAD completed a suite of tests to confirm and characterize the virus, including: Matrix RRT-PCR, virus isolation in eggs, RRT-PCR H5, cELISA, bELISA, HI, IVPI, Histology, IHC, and sequencing. The majority of sample submissions were sent to the AHL in Guelph. All three premises showing positive results were declared infected premises.  

The NCFAD typed the virus as H5N2. Further sequencing and analysis indicated that the infectious agent was a reassortant virus, which contained genes from Eurasian and North American lineages of avian influenza viruses. The virus contained gene segments from the highly pathogenic Eurasian H5N8 virus, including the H5 gene, and segments from typical North American viruses, including the N2 gene. This represents the first time a Eurasian HPAI H5 lineage virus has been a cause of outbreaks of avian influenza in domestic poultry in North America.

4.5 Movement Restrictions and Licensing

In order to control movement, a quarantine was placed on every location within the control zones, and on the additional high-risk premises identified earlier in this document.

To control movements on IPs, premises within 5 km of an IP and premises with an epidemiological link were initially quarantined and declared Infected Places.  Licences were issued when movements were required on these sites.  Once the NAI control zones were established, quarantines and declarations of infected places remained for the premises within 5 km and additional quarantines were placed on premises within 10 km. Movement was then controlled through licensing. The issuance of licenses was controlled by the Permit and Movement Control section and was largely based on participation in Dead Bird Surveillance (DBS) and flock health reporting, among other conditions. Industry coordinated the placement of birds on premises located between 5 and 10 km. As the outbreak progressed, permit conditions became less strict. During the response, a total of 532 movement licenses were issued by the CFIA.

4.6 Surveillance

4.6.1 Baseline Surveillance

Oropharyngeal swabs were collected once from live birds housed on premises located in the control zones, and on epidemiologically-linked premises. The swab samples were tested using matrix RT-PCR for influenza A and RRT-PCR for H5.

  • For commercial premises, an oropharyngeal swab was collected from 60 birds in each barn on the premises.
  • For non-commercial premises, an oropharyngeal swab was collected from 25 birds, if the flock size was 25 birds or more. For flocks with fewer than 25 birds, the CFIA collected a sample from each bird. If domestic waterfowl, such as ducks and geese, were present on site, cloacal swabs were collected instead of oropharyngeal swabs.

4.6.2 Dead Bird surveillance

Commercial poultry farms within AICZ 1 and 2 were placed under surveillance so any spread of the disease would be quickly detected.  Dead birds were collected twice per week from premises in AICZ 1 and 2 until May 21st, when it was reduced to once per week. The CFIA and industry associations worked together to ensure that producers met surveillance requirements.

CFIA delivered bins to farms in the control zones with instructions on how to participate in the surveillance program. Up to five recently-dead birds per barn on each premises were to be left for sampling in the bins at the farm gates. The sampling happened on a specific day or days each week, as determined by the CFIA. If there was no mortality on a given sampling day, the producer was to place a bin upside-down at the farm gate. This procedure was intended to limit the spread of the virus; the surveillance teams stayed at the property limits, never entering the premises. Once sampled, the dead birds were left behind in the bins for disposal by the producer.

Each day, a list of farms where dead birds were to be collected was developed by the Surveillance Unit. When bins were absent from the farm gate on the designated day, the producer was considered to be non-compliant. Compliance level overall was extremely high. For those producers that appeared to be non-compliant, CFIA or an industry representative would follow up to determine the cause. In addition to commercial poultry flocks, non-commercial backyard flocks were put under surveillance. These flocks were identified by themselves, by industry, or were found during surveillance activities. There was no way to accurately determine the percentage of small flocks identified out of the total community in the AICZ. Dead bird surveillance bins were supplied to these flocks with instructions on how to present the birds. Due to low volume of mortality expected, instead of being given specific days for pick up, small flock owners were instructed to call for sampling any time they had a dead bird.

DBS ended on July 13th for AICZ 1 and July 27th for AICZ 2.  A total of approximately 1300 birds of all flock types were tested at AHL, and all samples were negative. 

4.6.3 Flock Health & Production Records

Data on production statistics such as mortality, egg production, water and feed consumption were sent by fax or email to CFIA twice per week from all premises located in the AICZs, including small flock owners. When DBS dropped to once weekly from twice weekly, so did requirements for flock health questionnaires.

4.6.4 Pre-movement Surveillance

This surveillance was applied on poultry premises in the AICZ moving live poultry or poultry products. For this specific outbreak, flock health records and negative dead bird surveillance results were considered as sensitive indicators for monitoring the presence of virus in the flock. The premises that had routinely participated in this outbreak surveillance program were eligible for a license.

4.7 Depopulation and Disposal Activities

All birds on infected premises were humanely euthanized by sealing the barns and flooding them with carbon dioxide (CO2) gas. Compost piles were built inside the barns to inactivate the virus via Biological Heat Treatment (BHT) process. The CFIA protocol for this process requires the lower confidence interval of average temperatures in the inner and outer core of the compost pile to be greater than or equal to 37°C for six consecutive days to ensure virus inactivation. CFIA disposal specialists recorded temperatures throughout the compost pile on a daily basis. When the temperature and time parameters were achieved, the compost pile was moved outside the barn for secondary composting. Established CFIA protocols guided in-barn BHT and out-of-barn secondary composting. Secondary composting was the responsibility of the owner and did not require CFIA monitoring, and was conducted with the support and guidance of OMAFRA personnel to ensure compliance with applicable provincial legislation.

4.8 Cleaning and Disinfection of Facilities and Equipment

Once the barns were empty, the CFIA conducted an on-site assessment with the owner of each premises. This assessment determined which buildings, equipment and materials required cleaning and disinfection, and potential issues with difficult items and areas. 

Cleaning and disinfection (C&D) was the responsibility of the premises owner, who had to produce a protocol detailing how the premises would be cleaned and disinfected. The CFIA reviewed and accepted the protocols that included all the necessary information and considerations as per the site assessment. The producer contacted CFIA once the cleaning was done and if this step was approved, disinfection could begin.

Approval of the cleaning was provided by CFIA inspectors. It was based on a visual verification of the removal and appropriate disposal of all dirt and organic material from the surfaces to be disinfected, as well as the disposal of contaminated items that could not be disinfected. This step consisted of using detergent or degreasing agents to remove the virus and to expose any residual virus to disinfectant.

Disinfection consisted of spraying an approved disinfectant on all areas where animals would be present when the farm was repopulated, using sufficient quantity to meet the contact time specified by the manufacturer. Disinfection was also verified by CFIA inspectors prior to final approval.  

4.9 Release of Quarantine on Infected Premises

The release of quarantine for previously infected premises was allowed under the following conditions:

  1. The CFIA approved the C&D procedures; and
  2. The premises:
    • remained vacant of susceptible species for a minimum of 21 days following the approval of the C&D to ensure that any residual virus had been eliminated, or
    • was restocked, and a weekly statistically valid testing by matrix PCR for the presence of the influenza type A was negative for the placed birds. The last test was conducted at least 21 days after the birds are placed in the barn.

All three previously infected premises chose option 'a'.

4.10 Release of Movement Restrictions on Non-Infected Premises

Movement restrictions on non-infected premises were released once the declaration of infected place was removed from the infected premises with which the non-infected premises were linked.

4.11 Post-Outbreak Surveillance

Following the approval of C&D on the last Infected Premises, the three-month Post-Outbreak Surveillance period was initiated. In order to meet WOAH criteria, an epidemiologically-sufficient sample was determined to be 160 farms from the outbreak area, in addition to the normal sampling of the province using the CanNAISS program. All samples were collected by private poultry practitioners under contract with CFIA and sent to the CFIA NCFAD for analysis.

5. Summary of Findings and Working Hypotheses on Source and Transmission of NAI

5.1 Source of the Virus

Waterfowl are well established primary reservoirs for a wide variety of strains of avian influenza.  A recent report from the CFIA entitled "Qualitative Risk Assessment of a Highly Pathogenic Avian Influenza Virus in Canada" examined multiple potential sources of the H5N2 virus. Based on the epidemiological investigation conducted in this response, no other source of infection beyond introduction of the virus into the environment by migratory waterfowl provides a viable explanation. The existence of reports of waterfowl in the vicinity of the outbreak, particularly near IP1, is supportive of this interpretation.

Given the lack of identified connections between IP1 and the IP2/IP3 cluster, there is no evidence to support any spread from IP1 and IP2, which is supportive of IP2 being treated as a second incursion of virus mediated by migratory waterfowl.

5.2 Means of Spread

Waterfowl contaminate the environment by shedding the virus via their feces. The likelihood of exposure to indoor-reared poultry by migrating waterfowl is subject to several factors: the density of the poultry population in the affected area, the strength of biosecurity measures, the level and frequency of contact between farm workers and birds, and the proximity of the poultry to the migration routes of wild birds. While poultry production systems in Canada are designed to reduce or prevent contact between wild birds and commercial poultry, the potential does exist for the introduction of the virus from the environment if a breach in biosecurity occurs.
The majority of previous outbreaks of HPAI in Canada have occurred in the Fraser Valley of British Columbia, which is populated densely with poultry operations. This has resulted in significant local spread in previous HPAI outbreaks. In contrast, poultry production is much less dense in Oxford County, with few large operations in close proximity. Tracing investigations were conducted on all trace-in and trace-out activity around the IPs in our critical period, and no evidence of fomite or other activity-mediated transmission was found.

5.3 Field Epidemiology – Summary of Findings

Given the different production types and lack of identified connections between any of the three properties the outbreak is being viewed as most likely the result of two separate incursions of virus, mediated by migratory waterfowl (into IP1 and IP2) with limited local/environmental spread (IP3).

All possible linkages were examined to discover any other possible connection between the IPs, including veterinarians, feed suppliers, deadstock operators, common personnel and bedding suppliers. To further examine linkages, all IPs were re-interviewed by CFIA personnel. No linkages were identified in either the initial or follow-up investigation. In the absence of any new data, it is recommended that this outbreak continue to be viewed as two separate incursions of virus with limited local spread.