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Avian Flu

Public interest in Avian Flu has almost disappeared. This is not surprising, given all that has happened since the Swine Flu H1N1 pandemic began in March/April 2009.  However, it is important to remember that Avian Flu still remains in the background, requiring continued vigilance and surveillance. A new H7N9 has also recently emerged, in China. Here is a summary of the key facts:

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.

The current outbreak, which started in 1997 and is still continuing, is the worst outbreak ever recorded. It has affected many millions of birds, and the strain responsible has 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.

H5N1 Influenza

The current strain of avian flu is a subtype called H5N1.  There are several reasons why this strain is especially important:

  •  H5N1 has a known ability to mutate easily into other types
  • It has a documented ability to acquire genes from viruses that infect other animal species
  • It has a known ability to infect humans as well as birds
  • When humans have been infected, the illness has been very severe or even lethal (56% mortality)
  • Birds that survive infection with this strain can go on to spread the virus orally and faecally for a period of up to ten days and can spread infection over a wide area, both by migration and through contact with large numbers of birds at live poultry markets.

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 may even have been deliberately covered up.

The geographic spread of H5N1 has now been carefully documented (see our Links page for the latest information).

The spread of H5N1 is relentless and ongoing, despite the fact that only the most newsworthy milestones in its spread receive prominent media attention. The more birds that become infected, the greater the potential for spread between birds and humans. It has now been eclipsed by interest in H1N1 swine flu.

What is H7N9 bird flu?

H7N9 flu came to attention in China in April 2013, affecting poultry and causing serious illness in humans. Human to human spread has not so far been documented, but the situation is being monitored closely for developments. It is possible that H7N9 may overtake H1N1 as a source of concern.

How is Avian flu spread to humans?

With a tiny number of exceptions, human cases of H5N1 avian flu have so far resulted from direct contact between infected birds and humans. (The exceptions were a single, close family contact in Vietnam and a small cluster of cases with close family contact that occurred in Indonesia.)

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.

Treatment

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. Resources for obtaining the latest advice from the key health authorities are listed on our links page.

Sensible precautions for all travellers include:

  • Avoiding contact  Minimise the risk of contact with birds and poultry that might be infected; one practical way of avoiding this is to avoid "wet markets" in Asia - large food markets where live birds are traded. Many such markets have already been closed and poultry in affected Asian countries are already being culled on a massive scale. Avoid farms and direct contact with birds.
  • Improved hand hygiene: careful attention to simple hygiene measures reduce the potential for flu virus transmission. These include possible use of alcohol-based hand sanitisers and rinses.
  • Flu vaccination  A small degree of cross protection may occur from currently available vaccines; flu vaccine is safe and seems a reasonable and sensible precaution. A number of alerts have been triggered when travellers who have returned from regions affected by H5N1 have returned home with a fever that has turned out to be caused by seasonal flu.

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:

  • Standby / preventive antiviral medication  At least 2 possible antiviral drug options are known to be effective against influenza viruses. Drugs can be used either on an emergency standby basis in the event of possible symptoms, or to prevent the onset of illness in people who have been in direct contact with cases. The drugs are oseltamivir (Tamiflu) and zanamivir (Relenza). Medicines should be prescribed individually with detailed instructions about when and how to commence medication.
  • Physical protection: Personal protective measures, including a range of possible high filtration facemasks, goggles, protective coveralls, boots and/or overshoes may need to be considered for those at high risk. These items require careful training in correct use and must be carefully fitted.  Contact us for more information.