Influenza A in pigs

Influenza A viruses belong to the family Orthomyxoviridae.

Influenza viruses are a large group of viruses that are classified as type A, B or C. Within this large group, different influenza viruses infect different species of animals, and humans. Only influenza A and C viruses have been isolated from naturally infected pigs.

Influenza A viruses are found in pig populations worldwide. Influenza A viruses originating in pigs have been detected in Australia but have not been linked with significant production or public health issues.

• pigs
• humans
• birds

The incubation period in pigs is usually 1–3 days.

Pigs begin excreting virus within 24 hours of infection and may shed virus for 7–10 days. Peak shedding occurs around 48–72 hours following infection.

Influenza A viruses are primarily transmitted among pigs in close contact through nasal discharges and aerosols from sneezing and coughing.

Immunity acquired by recovered animals is typically short lived, making them susceptible to reinfection and disease if re-exposed.

Pigs, humans and birds (particularly poultry) can infect each other with influenza A virus. The severity of disease in the host varies with both the subtype of influenza A virus and the animal species.

In herds without immunity, infection typically presents as an acute to chronic respiratory disease.

Clinical signs in pigs include:

• fever
• loss of appetite
• weight loss
• coughing, sneezing, nasal discharge, breathing difficulty.

In outbreaks most pigs are likely to be affected (up to 100%, high morbidity) but only a small proportion are likely to die (1-3%, low mortality). Most pigs recover within 5–7 days.

• Movement of infected pigs, humans or birds.
• Movement or use of contaminated objects such as equipment and clothing.

All year round, with seasonal peaks in the colder months in temperate zones.

Monitor your pigs for clinical signs consistent with influenza A.

If you believe influenza A is present, you must report it to Biosecurity Queensland on 13 25 23 or contact the Emergency Animal Disease Watch Hotline on 1800 675 888.

People working in piggeries and those having frequent contact with pigs should consider personal seasonal human influenza vaccination, while remaining attentive to appropriate personal hygiene and biosecurity practices.

Contact your local physician or Queensland Health if you work with pigs and experience influenza-like symptoms.

The response to detection of influenza A in pigs will be consistent with the AUSVETPLAN response policy brief Influenza A viruses in swine including:

• epidemiological investigation and risk assessment to determine the appropriate control strategy
• consultation with the pig industry, private and government veterinarians and other relevant government agencies (including Queensland Health and Workplace Health and Safety Queensland) to minimise the impacts of infection to animal and human health
• control strategies appropriate to the circumstances and level of risk.

Low risk

Where the assessed risk to animal or public health is low, the incident will be managed by the person responsible for the pigs under their general biosecurity obligation (GBO),  with advice provided by Biosecurity Queensland.

High risk

If the assessed risk to animal or human health is high, the incident will be managed with the approval of the Consultative Committee on Emergency Animal Diseases. Control strategies may include:

• implementation and maintenance of biosecurity controls, including movement controls to prevent its spread to other pigs on or between farms and to humans working with infected pigs
• tracing and surveillance to determine the source and extent of infection
• awareness-raising activities to encourage reporting and enhanced monitoring for changes in the health status of pigs and poultry on nearby properties
• industry support to increase understanding of the issues, facilitate cooperation, and address any animal welfare and on-farm biosecurity issues.

Vaccination

Vaccines to protect pigs against influenza A viruses are not available in Australia.

Treatment

Treatment of infected pigs is usually ineffective, though antibiotic treatment is frequently used to lessen the impact of secondary bacterial infections.

Australia has strict import conditions to prevent the entry of influenza A and other diseases of pigs.