Animal influenza viruses differ from human seasonal influenza viruses and often do not easily transmit between humans. However, zoonotic influenza viruses (animal influenza viruses that may occasionally infect humans through direct or indirect contact) can cause disease in humans ranging from a mild illness to death.1
Avian influenza, also known as bird flu, refers to the disease caused by infection with avian influenza Type A viruses. These viruses occur naturally among wild aquatic birds but can be passed between many species of birds; commercial, wild or pet. Domestic poultry such as chickens, ducks, turkeys and geese can also be infected.
Although these viruses don’t infect people easily and aren’t usually transmitted human-to-human, sporadic human infections with avian flu viruses have occurred with 4 particular viral strains which have caused serious concern in recent years.2
- H5N1 (since 1997)
- H7N9 (since 2013)
- H5N6 (since 2014)
- H5N8 (since 2016)
Influenza A viruses are divided into subtypes based on their surface proteins: hemagglutinin (HA) and neuraminidase (NA). With 18 known hemagglutinin subtypes and 11 known neuraminidase subtypes, many different combinations of HA and NA proteins are possible. The H5N1 virus, for example, indicates an influenza A virus subtype that has an HA 5 protein and an NA 1 protein.3
Currently, there is no effective treatment available for infected birds.
Who is at risk?
Infection with avian influenza is primarily through contact with infected birds (dead or alive) or a contaminated environment. Even seemingly healthy birds may pose a risk to people who come into contact with them, as infected birds don’t necessarily show symptoms of sickness.
These exposures may increase your risk of acquiring bird flu:
- touching infected birds that are dead or alive
- exposure to dried dust from the droppings or bedding of infected birds
- exposure to droplets sneezed by infected birds
- preparation as culling, slaughtering, butchering or handling infected poultry for cooking
- visiting live markets, where infected birds may be sold in crowded and sometimes unsanitary conditions
Outbreak potential
Due to the viruses’ ability to infect humans, bird flu is a potential risk to humans. An outbreak of bird flu could range from being relatively contained, affecting only birds or small clusters of humans, or could occur at a pandemic level. A pandemic is the worldwide spread of a disease due to a novel virus for which humans have little or no immunity to, sped up with the growth of global travel.
Should I be concerned?
The reported signs and symptoms of avian influenza A virus infections in humans have ranged from mild to severe in nature and include conjunctivitis, influenza-like illness sometimes accompanied by nausea, abdominal pain, diarrhoea, and vomiting, severe respiratory illness, neurologic changes, and the involvement of other organ systems.
The best preventive measure taken against avian influenza A is to avoid sources of exposure. Most human infection with avian influenza A have occurred following direct or close contact with infected poultry. However, bird flu isn’t transmitted through cooked food, so cooked poultry and eggs are safe to eat even in areas that have experienced outbreaks of bird flu.
References:
World Health Organisation, Influenza (Avian and other zoonotic).
1World Health Organisation, Avian and other zoonotic influenza.
2National Health Service, Bird Flu.
3Centers for Disease Control and Prevention, Influenza Type A Viruses.