Have you noticed that Avian Influenza (AI) has been in the news a lot lately? This is largely due to the unprecedented spread of outbreaks, primarily in poultry flocks, around the globe over the past six months.
Fortunately, Australian poultry flocks have to date escaped this wave of AI, but sadly AI is currently having devastating consequences for the poultry industries in many other countries. For example, the US poultry industry has been particularly hard hit, at last count having AI confirmed on over 200 separate locations since December 2014, affecting almost 47 million birds. The disease has mostly been in turkey and egg farms, and has spread from the Pacific Northwest and California through to the mid-west states such as Montana, North and South Dakota, Minnesota, Iowa and beyond, with the strain of virus evolving as the outbreak has spread (to follow the course of this outbreak in the US, the following site is a useful one to watch: https://batchgeo.com/map/2015-avian-influenza-outbreaks).
So what is avian influenza? Where does it come from, and what are the risks and consequences of our poultry flocks being infected with it? Read on…
What is avian influenza?
Avian influenza is an infectious disease of birds caused by a Type A influenza virus. So, just like humans, birds, including chickens, can get the ‘flu!
However, the types (strains) of influenza virus that can cause disease in birds are generally not the same types that cause the flu in humans, as I’ll explain below.
What’s in a name?
Not all influenza viruses are the same. Some have a greater affinity for infecting and/or causing disease in certain host species than in others, and some types cause worse disease in their favoured host species than other types.
Influenza A viruses are divided into subtypes based on the structure of two proteins on the surface of the virus – the hemagglutinin (H) and the neuraminidase (N) proteins. There are at least 16 different H subtypes and 9 different N subtypes. Each virus has one of each subtype in any combination, and influenza A viruses are named accordingly eg H1N1; H5N2 etc.
Some subtypes cause disease in certain species of animals and not others. For example, most of the viruses that are responsible for seasonal flu in humans are H1 or H3 subtypes.
On the other hand, while most subtypes can be carried by wild birds, the two subtypes that are capable of causing serious clinical disease in poultry flocks are H5 and H7. Conversely, these two subtypes are rarely associated with disease in humans.
Strains of influenza virus found in birds are further divided into two groups based upon the severity of illness in birds they cause: low pathogenic (LP) and highly pathogenic (HP). Low Pathogenic avian influenza (LPAI) infection typically only causes minor illness – indeed, sometimes infected birds show no clinical signs at all. Highly pathogenic avian influenza (HPAI), on the other hand, is highly infectious and causes severe disease and often high mortality rates, particularly in chickens and turkeys.
Where does avian influenza come from and how does it spread?
Avian influenza viruses are commonly carried by wild birds, particularly waterfowl such as ducks and geese. In Australia, ongoing surveys of wild birds show that a small proportion of wild birds show evidence of having been exposed to avian influenza virus (for example, see https://rirdc.infoservices.com.au/items/15-016). Generally, wild birds carry the low pathogenic forms of AI viruses (indeed, in Australian wild bird surveys, all AI viruses found have been LPAIs).
However, infections can be spread from wild birds to poultry flocks, either through direct contact, or indirectly, for example through contamination of a flock’s water supply or the range which the flock has access to by wild bird droppings.
Once in a flock of highly susceptible poultry species such as chickens or turkeys, some LPAI virus strains are capable of mutating into their HPAI form, giving rise to outbreaks of clinical avian influenza disease. Thereafter, spread to other poultry flocks can occur through wild birds movements or by other mechanical means, like through movements of infected poultry, or contaminated equipment shared between poultry farms.
Do we have it in Australia?
Many people may be surprised to learn that we have had 7 outbreaks of high path avian influenza in Australian poultry flocks over the course of the past four decades, the most recent being in layers (chickens raised to produce table eggs rather than chicken meat) in Young in 2013. The reason you may not recall having heard about these, is that on each occasion the initial infected flock was quickly identified, reported to authorities and acted on to eradicate the disease, so that there was no opportunity for significant further spread.
Does AI affect people?
It is extremely rare for strains of avian influenza virus that cause disease in poultry to also cause disease in humans. For example, despite the extent of the current outbreak in the US referred to in my first paragraph, the number of properties affected and the numbers of birds infected, the strains involved are not known to cause disease in humans and no humans have been affected. Similarly, none of the strains associated with outbreaks in Australian poultry flocks have been known to cause illness in humans.
However, some strains of H5 and H7 avian influenza viruses found overseas have been able to occasionally infect people (for example, the H5N1 strain that many readers may recall having attracted much media attention over the past decade), but this is rare, and requires very close physical interaction with infected birds.
Can you catch it from eating chicken?
NO! The World Health Organisation confirms that properly cooked chicken meat cannot transmit AI.
What are we doing to keep AI out of Australian flocks?
Well, at a farm level, the Australian chicken industry implements biosecurity procedures on farms largely aimed at reducing the risk of transmission of viruses from wild birds to commercial flocks.
Constant vigilance is important too – the industry has arrangements in place for monitoring the health of flocks and a system for reporting unusual or suspicious health issues to both company veterinarians for investigation and onward reporting to government authorities.
In the event of confirmation of a case of AI, we also have a well rehearsed and up-to-date response and management plan in place which has been agreed to by both industry and governments to ensure a rapid response to an outbreak. Those outbreaks we’ve had over the past 40 years have given us the chance to test and refine the plan, so that we know it works!
For more information on Avian Influenza from an Australian perspective, see the the ACMF website: http://www.chicken.org.au/page.php?id=170. The ACMF website also answers a range of FAQs related to AI on a dedicated webpage: http://www.chicken.org.au/page.php?id=151