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Public awareness of Avian Flu (“Bird Flu”) reached a peak in 2005, following its spread from Asia to Europe. Focus rapidly switched to the more pressing problem of Swine Flu, and the H1N1 pandemic that began in March/April 2009. However, Avian Flu has not gone away and remains firmly in the background, requiring continued vigilance and surveillance. H7N9 strains emerged in China in 2013 but appear to have been contained. There has recently been a significant outbreak of H7N7 bird flu at a poultry farm in the UK (necessitating a cull of over 170,000 laying birds).
What is Avian Flu (“Bird Flu”)?
Avian flu is an infection of birds, caused by a type A strain of the influenza virus. It is not new – it has been known for more than 100 years; it can occur all over the world and all bird species are believed to be susceptible to it. It is normally only transmissible between birds, among which it causes a spectrum of illnesses ranging from minor to rapidly fatal disease, sometimes killing entire bird populations.
An H5N1 outbreak, which started in 1997, is still continuing, and is the worst outbreak ever recorded. It affected many millions of birds, and the strain responsible proved to be an especially dangerous and virulent one.
Why are there so many strains of flu, and what’s the difference?
A hallmark of flu viruses (human, bird and other animal varieties) is their ability to evade immune defences over time by making changes to the proteins that are present on their surface coats.
The outer surface of the flu virus contains two main types of protein, that interact with the host’s immune system. These are called haemagglutinin and neuraminidase respectively – known as “H” and “N” proteins for short. (These are the “spikes” visible on the outer surface of the virus, as seen on electron micrograph images.)
Each of these proteins exists in the form of several possible variants, resulting in vast numbers of possible combinations and therefore vast numbers of possible strains. Immunity is normally specific to each individual strain.
Over a period of time, gradual, subtle changes in the character and combination of these protein variants (technically known as “antigenic drift”) enables flu viruses to always keep one step ahead of the their host’s immune system, which is why new flu vaccines have to be produced every year against each new season’s predominant strains.
The H5N1 outbreak was especially important because:
What is the current state of the H5N1 outbreak?
The current outbreak was first evident in Hong Kong in 1997 and then resurfaced in Korea in mid-December 2003. Since then it has spread to several other countries. It is possible that the problem had been escalating in China and Indonesia for very much longer than this however and was almost certainly covered up deliberately.
What is H7N9 bird flu?
H7N9 flu came to attention in China in April 2013, affecting poultry and causing serious illness in humans. It appears to have been well-contained.
What is H7N7 bird flu?
Human infections with highly pathogenic H7N7 subtype avian influenza viruses have been associated with influenza-like illness and conjunctivitis, and in one instance, severe disease causing death. No human infections have been identified in connection with the current incident in the UK. The risk to the general population is considered to be very low, but public health control measures have been implemented, together with heightened surveillance for any sign of spread amongst the human population.
How is Avian flu spread to humans?
Human cases of avian flu are extremely rare and generally involve close contact with birds.
Birds excrete the flu virus in faeces. Transmission is believed to occur through inhalation and/or ingestion. Correctly cooked poultry is not capable of spreading the virus.
The major symptoms are fever, sore throat, cough and ultimately severe respiratory distress (shortness of breath, difficulty breathing) and pneumonia. Laboratory tests are available to confirm the condition.
Antiviral drugs are available both for treatment of clinical cases, and for prevention of illness in people who have been exposed to cases. Drugs are most effective when given early (ideally within 12 hours) of the onset of symptoms.
Avian Flu and International Travel
Even in countries where large numbers of cases have occurred in birds, there is at present no reason to restrict travel.
Sensible precautions for all travellers include:
High Risk Travellers
The Fleet Street Clinic specialises in looking after high risk travellers, including many within the news industry whose occupation might make contact with avian flu more likely. Additional options for such travellers include: