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Influenza
A and Livestock in Ontario - Important Update for Veterinarians
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| Author: | Dr. Paul Innes -Lead Veterinarian/Provincial Biosecurity /OMAFRA |
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| Creation Date: | 06 July 2005 |
| Last Reviewed: | 20 May 2008 |
While many influenza viruses in animals are widespread, in 1998 some jurisdictions the USA reported an emerging influenza virus in swine. Since this time, the Animal Health Laboratory (AHL) at the University of Guelph has identified a range of influenza virus subtypes in swine, poultry and horses, including H1N1, H1N2, H3N2, H3N3, and H4N6. An average of 16 cases of these virus strains are diagnosed by the AHL each year.
Subclinical infection with influenza is common in swine. A serological survey by the University of Guelph indicated that 80% of study herds in Ontario had antibodies to H1N1 influenza virus. A low prevalence of the H3N2 (Quebec) subtype has also been detected. In 1998, a H3N2 subtype emerged in Texas that has since been reported in several US States as well as western Canada (2005). It is believed to be widespread in the swine population in areas that have been affected. Although found mostly in swine, it has also been reported in poultry. In swine, the H3N2 virus tends to cause acute respiratory disease of short duration, from which most animals recover fully. In most poultry it tends to cause mild clinical disease and in some cases permanent severe decline in egg production.
Samples submitted in late April of 2005, from swine herds in southwestern Ontario experiencing acute respiratory disease, subsequently tested positive for a H3N2 Texas-like influenza, after virus isolation and sequencing at the AHL. This was the first report of this emerging H3N2 subtype in Ontario livestock. As of June 27, H3N2 has been diagnosed from samples submitted to the AHL from at least 22 swine herds in Ontario. Clinical signs reported with sample submissions included listlessness, anorexia, pyrexia, and severe coughing for a few days. Mortality and abortions have been reported to be less than 1% of affected animals. There is anecdotal evidence from veterinarians and the swine industry that other cases are occurring in swine herds across Ontario. Samples are not necessarily being submitted to the laboratory in all cases. Anecdotal evidence from practitioners indicates the incidence may be declining, and chronically affected herds may be a concern. Influenza due to the H3N2 strain is not a reportable disease in swine under the federal Health of Animals Act. The Canadian Food Inspection Agency (CFIA) has not quarantined any swine herds associated with swine influenza.
Routine samples submitted to the AHL on June 21 from a poultry flock in southwestern Ontario subsequently tested positive for H3N2. To date there are no signs of respiratory disease, and mortality rates have not increased above normal in the flock. Additional test results indicate this is not an H5 or H7 subtype that can cause Highly Pathogenic Avian Influenza and it is not the H5N1 subtype that is causing disease in birds and people in Asia. This strain is not reportable under the federal Health of Animals Act and the flock has not been quarantined by the CFIA. The CFIA is monitoring the situation closely and the affected farm's management is taking additional measures to prevent spread from the farm.
The Ontario Ministry of Agriculture and Food (OMAF) will pay the cost of laboratory tests for influenza at the AHL. This may encourage veterinarians to submit samples to the AHL for surveillance purposes regarding H3N2 infections in Ontario swine and poultry. This fee reduction commenced on June 24, 2005 and will continue until July 31, 2005. Veterinarians are encouraged to submit nasal or cloacal swabs in virus transport media (available from the Animal Health Lab) or lung tissue (frozen and formalin-fixed) from suspect animals. Antigen detection ELISA, immunohistochemistry, direct immunofluorescence, RT-PCR and virus isolation in cell culture and eggs, followed by typing of positive samples using multiplex PCR and hemagglutinin gene sequencing are available. Practitioners should select HI serology tests that use the Texas-98 strain of influenza virus. An H3N2 antibody ELISA is now also available for serological monitoring following vaccination. Veterinarians should complete AHL sample-submission-forms as usual. The AHL will not charge the submitter for influenza tests conducted, but other laboratory fees will be charged at the usual rate.
Biosecurity is always important to prevent the spread of infectious diseases within and between farms. This is particularly important to prevent spread of highly contagious influenza virus within, among and between swine and poultry. Producers and veterinarians are encouraged to be vigilant in their biosecurity practices. Veterinarians should be particularly careful not to move directly between swine and poultry farms if at all possible.
To date, there is no report of human illness associated with this particular H3N2 strain. All individuals working with livestock or poultry should receive annual human influenza immunization (available free to all residents who work, live or attend school in Ontario). In addition, individuals working with infected livestock should follow strict infection control measures to prevent exposure to influenza virus. These include frequent handwashing and always washing hands after handling animals, and wearing appropriate personal protective equipment such as mask, gloves, safety goggles, coveralls, shoes/boots, and hair covers. Please contact your local public health unit for more information. If an individual develops influenza- like illness while working with infected livestock, he or she should immediately seek medical attention. Influenza is a reportable disease in Ontario and all human influenza infection must be reported to the local medical officer of health.
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