Explainer: should we be worried about the new strain of bird flu?

Bird flu transmission to humans is rare and hasn’t occurred with this new strain. AAP

The circulation of a new strain of the H5N1 avian flu virus from China and Vietnam has prompted calls from the Food and Agriculture Organisation of the UN for health authorities to be ready for a possible major resurgence of the deadly virus.

According to the World Health Organisation, the H5N1 virus has infected 565 people since it first appeared in 2003, killing 331 of them. The latest human infections occurred earlier this month in Egypt and Cambodia.

Professor Terry Nolan, Head of the University of Melbourne’s School of Population Health, explains why a possible mutation has authorities concerned:

This bird flu clade (or strain) – 2.3.2 – is a relatively minor mutation in the genetic sequence of the flu virus. This 2.3.2 clade appears to have emerged in China and Vietnam. But there don’t seem to be any cases of human contraction.

This report has come from the Food and Agriculture Organisation (FAO) of the UN, which is concerned about the virus infecting food sources. They’re very concerned about the many millions of domestic bird flocks, particularly chickens in Southeast Asia, which are in close proximity to humans.

How is bird flu transmitted?

The bird flu occurs in birds and its transmission to humans is actually quite rare. Transmission between humans is incredibly rare.

But if there was a mutation in some of the critical sequences of the virus, it’s possible it could mutate into a form that would be readily transmitted between humans. And that’s the sort of pandemic step that everyone’s concerned about.

That’s what happened with swine flu: the strain became highly transmissible between humans. Fortunately it wasn’t as virulent as the H5 (bird flu), which has a much higher capacity to cause serious illness.

In fact, on average 50% to 60% of all humans who have contracted bird flu have died.

What makes bird flu so deadly?

The virus turns on different immune mechanisms. There are one or two key switches in the immune system that are turned on by H5 – it’s these switches that cause high levels of tissue destruction.

This is something distinctive about H5, which makes it more potent.

What has protected Australia against past outbreaks of bird flu?

The current bird flu clades circulate in migratory birds. And if you look at the fly paths of migratory birds around the world you’ll see that Australia isn’t in their flight path. Birds carrying H5 have never flown over Australia so we have never been exposed to it.

The carrier birds do migrate across Asia and across Europe and H5 is now well and truly established in Western Europe and Africa. The most recent countries to be affected are in the Middle East and there are severe human outbreaks in Egypt.

The concern is that if there is human-to-human transmission and a mutation occurs, then humans migrate much more efficiently than birds – on airplanes – and can spread the virus more rapidly.

Do you have any advice for Australians travelling to these affected countries?

Stay away from domestic fowl. Chickens and ducks are the most likely source of exposure for humans.

An H5 vaccine exists but it’s not produced commercially so you can’t buy it or get a prescription. The government stockpiled it after the initial bird flu threat emerged.

If a mutation occurs, and turns it into a pandemic strain, that stockpile will only offer partial protection. The mutation will make it more distant from the virus strain that was used to generate that vaccine.

How likely is the virus to mutate and spread between humans?

Given this virus is now established in the world’s bird populations it remains a serious threat to humans. Because the virus causes serious illness, if it does mutate into a form that can be spread to humans, it will make the swine flu outbreak look like a Christmas picnic.

Do Australia’s health authorities have appropriate systems in place to deal with this threat?

The pandemic preparedness in Australia is at a very high level. In fact, we were criticised for over-responding when the swine flu outbreak occurred in 2009. We prepared for a H5 pandemic, or for something very similar to the Spanish flu of 1918.

When a pandemic starts, you don’t know how serious it’s going to be so you have to assume the worst. Even though swine flu caused a lot of deaths it wasn’t as bad as expected. If it had been H5, it would have been more than ten times worse.

One of the biggest shortfalls we’re trying to overcome is the inability to quickly produce a virus-specific vaccine for a mutated strain.

This is currently a time-consuming process of identifying the virus, engineering the sequence so it can be used to produce the vaccine, producing the vaccine and then, if necessary, testing the vaccine to ensure its safety. But it still takes too long.

By the time we had the swine flu vaccine, the first wave of the epidemic was well and truly over. We’re doing all we can do but we simply don’t have the technology to quickly produce a vaccine to protect against a mutated strain.