Avian influenza (AI) viruses are common in wild waterfowl throughout the world. For the most part, AI viruses cycle harmlessly in these well-adapted hosts. AI outbreaks among poultry occur worldwide from time to time.
AI viruses can be classified into two forms based on the severity of the disease they cause in poultry:
- low-pathogenic AI (LPAI)
- highly pathogenic AI (HPAI).
Most AI strains are classified as LPAI and cause few clinical signs in infected birds.
In contrast, HPAI causes a severe and extremely contagious illness and death among infected birds, with high mortality (up to 100 per cent) in domestic chickens and turkeys.
In some cases, if LPAI is allowed to circulate in poultry populations, the virus can mutate into the highly pathogenic form. This is why the presence of an H5 or H7 virus in poultry is always cause for concern, even when the initial signs of infection are mild.
LPAI poses no known serious threat to human health. However, some strains of HPAI virus can be infectious to people.
H5N1 virus is a form of the HPAI virus, but is considered to be a different strain. H5N1 has caused human cases in various countries, and has been associated with direct or indirect contact with infected live or dead poultry.
Mode of transmission of avian influenza virus
Direct contact with infected poultry, or surfaces and objects contaminated by their faeces, is presently considered the main route of human infection. Infected birds shed large quantities of virus in their faeces – thus, there are many opportunities to be exposed to infected droppings or to environments contaminated by the virus. Exposure is considered most likely during slaughter, defeathering, butchering, and preparation of poultry for cooking.
However, AI viruses are not easily spread from birds to people. Even with the highly pathogenic H5N1 AI virus, to which many thousands of humans have been exposed, few cases occur.
Control measures for avian influenza
Personal protective equipment guidance
Protection of personnel who might come into contact with AI-infected birds is important to the success of the Victorian health management plan for pandemic influenza. Although the risk of transmission of LPAI is low – as a precaution – people working on or entering an infected premises or involved in other activities should adopt the following protective measures:
- Wear appropriate personal protective equipment, including foot or shoe covers, respiratory protection (surgical mask) and eye protection.
- Wash hands before and after handling animals or touching surfaces contaminated by bird secretions (faeces, respiratory secretions or saliva) or contaminated products, such as litter.
- Ensure response personnel receive the seasonal flu vaccine.
- Discourage anyone who is ill with a suspected viral infection from entering a poultry house, a response location or processing facility.
Examples of at-risk people include cullers, composters or veterinarians performing field postmortems.
Anyone exposed to potentially infected birds or contaminated products should be vaccinated with the seasonal human influenza vaccine. Although the seasonal human influenza vaccine will not protect against LPAI, it may avoid simultaneous infection with both human and AI. There is a small possibility that if a person is infected with both of these viruses, the viruses could share genetic material (reassortment) to produce a new and highly infectious virus that would pose a threat to the wider community.
Having the human influenza vaccination will also protect workers from the usual human seasonal influenza and help avoid diagnostic confusion if workers develop influenza-like symptoms.
Workers who have been in close contact with AI-infected birds should monitor their own health during the period of exposure to infected birds or contaminated poultry products, up to 7 days after the last exposure.
Self-monitoring involves watching for:
- fever (monitor temperature daily for a temperature of at least 38 °C)
- respiratory symptoms – for example, sore throat, cough, difficulty breathing
- fatigue or collapse due to exhaustion
- chills or shakes
- muscle or joint aches
- nausea, vomiting, diarrhoea
- red, sore eyes (conjunctivitis).
Workers who have been in direct contact with birds or poultry products contaminated with AI and who become ill with any of the above symptoms should:
- report their illness to the workplace management, who in turn should notify public health authorities
- see their local doctor and report that they may have been in contact with birds carrying AI virus
- wear a surgical mask and isolate themselves from others until medically assessed
- practise good respiratory hygiene by covering their mouth when coughing or sneezing
- wash their hands after coughing, sneezing, or using tissues or handkerchiefs
- dispose of tissues hygienically.
Prevention measures for the public
People travelling to areas affected by AI are likely to have only a very small risk of infection. This risk can be reduced further by:
- avoiding places where there may be contact with infected birds, particularly live bird markets
- washing hands thoroughly after any contact with birds, their faeces or body fluids
- ensuring all uncooked poultry and eggs are handled hygienically during food preparation, with careful attention to hand washing after handling.
- ensuring all poultry and eggs are cooked thoroughly before eating.