Efficient control of HPAI in Canada
Experience has shown that rapid diagnosis, establishing quarantine and surveillance zones and disposal of affected flocks are critical to containing an outbreak.
The Veterinary Authorities (Canadian Food Inspection Agency) in Canada are to be highly commended on their prompt and full disclosure to the The World Organisation for Animal Health (OIE) and the USA of the history, diagnostic procedures and control measures relating to the highly pathogenic avian influenza (HPAI) incident in Regina Beach, Saskatchewan, during the last week of September. Experience has shown that in nations and regions where the disease is exotic, rapid diagnosis, establishing quarantine and surveillance zones and depletion and disposal of affected flocks are critical to containing an outbreak, minimizing disruption and cost and to restore normal production and exports.
For the most recent incident, the Canadian authorities applied the lessons of the more extensive Fraser Valley, B.C. outbreak of H7N3 HPAI during 2004. This previous episode in an area with a relatively denser population of poultry than in Saskatchewan cost $380 million to eradicate. During the past three years, contingency plans to detect and respond to outbreaks have been refined and additional diagnostic procedures have been introduced. Depletion of flocks with compensation and funding for control measures are mandated by the Health of Animals Act.
The sequence of diagnostic procedures extended from Sunday 23rd September when a veterinarian visited the farm to investigate acute elevated mortality in broiler breeder cockerels through to complete characterization of the agent by Thursday 27th September. The presumptive diagnosis leading to depletion of the flock was in fact made on Monday 24th at the National Center for Foreign Animal Diseases in Winnipeg, applying an ELISA procedure. The neuraminidase inhibition assay was completed on Tuesday 25th, followed by a positive RT-PCR assay on the 25th and repeated on Wednesday 26th. On Wednesday AI virus isolation was also completed together with a hemagglutination inhibition test. Isolation was not absolutely necessary for the diagnosis but is a precursor of sequencing the critical genes coding for the terminal hemagglutinin chain in order to characterize the strain of H7N3.
Epidemiologic studies are in progress to ascertain the source of the virus. This will involve investigating the movement and activities of personnel during the two weeks before the outbreak, the presence of H7 virus in waterfowl on the adjacent Mountain Lake, the possibility of direct and indirect contact with other poultry installations and obvious lapses in biosecurity. The Interagency Wild Bird Surveys conducted in cooperation with the US Department of the Interior and USDA’s Animal Health and Inspection Service (APHIS) failed to isolate H7 strains of AI from migratory waterfowl in both 2005 and 2006 but the survey results for August 2007 have not yet been released. Rules established by the OIE were followed including reporting on Friday 28th September, establishing a 3km area around the index farm within which there was no movement of poultry or products. In this case the nearest farm was located at a distance of 5km from the affected unit. Authorities designated a 10 km area in which surveillance of flocks for clinical abnormalities, mortality with attempts at antigen detection and possible seroconversion will be carried out.It is hoped that this limited outbreak has been confined to the affected farm and that the source of virus, possibly waterfowl will be identified. The episode reinforces the need for vigilance for AI through the entire NAFTA region, exercise of sound biosecurity and above all preventing direct and indirect contact between waterfowl or backyard poultry with commercial flocks.