Bird flu
WHEN IT comes to mass destruction, a strong contender for
the all-time record must be the 1918-19 ‘Spanish flu’ virus. Flourishing under
the impoverished conditions that followed the first world war, the epidemic
(which did not actually start in Spain) killed 40-50 million people worldwide.
Scientists believe it is a matter of time before another influenza virus poses a
similar threat to humanity.
The current East Asian bird flu is the most recent of
similar outbreaks. In 1997 in Hong Kong 1.4 million chickens, the entire stock,
were destroyed. Eighteen people became infected of whom six died. A further
outbreak in 1999 saw 1.25 million birds culled. In 2003 the Netherlands was hit
by an outbreak that killed one veterinary surgeon and led to a mild illness in
83 poultry workers and members of their families. Different strains of virus
have been responsible in each case.
New cases came to light this January in Thailand and
Vietnam, but have now been reported among the bird populations of Japan, South
Korea, Laos and Cambodia. The Indonesian authorities covered up the outbreak but
have now been forced to admit that the virus was found last August. Since then,
4.7 million birds have died there but, according to the government, only 60% as
victims of bird flu or the cull to contain it.
Thailand has also been in involved in a cover-up,
slaughtering nine million chickens since November but not admitting a case until
the third week of January, when two young boys died. ‘The government knew’, the
father of one said, ‘so why didn’t they tell the public so that we could protect
ourselves?’
Strong pressure was exerted to conceal the outbreaks as
chicken exports are worth $1 billion a year to Thailand and up to $7 billion a
year to Indonesia. Much of this ends up as processed chicken in Europe. Over 80
million chickens have been slaughtered so far. Financial markets in East Asia
have fallen slightly. ‘I think the concern with investors is whether this
becomes a SARS-like situation’, said Peter Haines of Aberdeen Asset Management
in Singapore. ‘I guess that would only come about if we suddenly discovered that
this disease can be passed on from human to human. That clearly would have big
economic implications for the region’.
There is evidence that all the outbreaks may have originated
in China, where a further cover-up has taken place since the first half of 2003.
As the main method of disease prevention is to slaughter all poultry in the
affected area, any delay allows the virus to spread. The effect on the
livelihood of small farmers can be devastating. Poultry smuggling from China may
have spread the outbreak around neighbouring countries. Thai government
compensation to farmers is only 10% of market rates, so farmers are reportedly
rushing to sell their birds before the cull is widened, spreading the virus
further.
Live-animal (wet) markets are traditional in many countries.
These provide an additional method of spread between infected birds, with large
numbers of people in close contact with them. Hong Kong has introduced two clean
days a month, when the markets are closed, cleared of all birds and animals, and
cleaned. This has reduced the numbers of different influenza virus strains
present compared with China, where these steps have not been taken. Last year’s
SARS virus is also thought to have spread from wet markets. But where most
people have no refrigeration, wet markets cannot simply be closed down.
World Health Organisation (WHO) officials have warned that
the disease is spreading at an unprecedented speed. ‘We don’t know how this
virus is spreading, and so it’s safe to presume that nowhere can consider itself
safe’, a spokesman said. So far there is no evidence that the strain of virus
causing the current outbreak is spreading among humans. Fourteen people had died
in Vietnam and six in Thailand by 17 February, but with no clear case of
human-to-human transmission occurring.
One way to cut the risk of the virus developing human
infectivity would be to vaccinate against human influenza all those working in
the poultry industry, including those involved in the culls (which have included
prisoners and the armed forces in some countries). Anti-viral tablets can also
be given to prevent flu, but they are expensive. Vietnam had a stock of 100,000
tablets of Tamiflu (made by pharmaceutical giant Roche) and a similar amount of
human vaccine – ‘a drop in the bucket’, according to the WHO.
A vaccine against the strain of bird flu virus responsible
for this outbreak would help prevent it causing an epidemic in humans. Because
the virus can change so rapidly new vaccines need to be continually developed to
keep up with these changes. A genetically engineered ‘seed’ virus with the same
surface proteins as the current strain was expected to be ready within two
months. From this, 750 million doses could be produced in several months,
growing the seed strain in fertile chicken eggs. But to find enough eggs, the
manufacturers would have to stop producing normal human flu vaccine, increasing
the risk to the elderly and others who get vaccinated each autumn.
Vaccines can be produced with human cultured cells instead
of eggs. A factory in the Czech Republic – opened in 2002 by the US company,
Baxter – could produce 50 million doses this way. It is ironic that they are
still unavailable, especially as a mild strain of bird flu broke out in
Delaware, USA, in early February. But the company has been co-opted to make
smallpox vaccine for the US ‘war on terror’ bio-defence stockpile.
Jon Dale
INFLUENZA VIRUS causes epidemics because its surface
proteins can change rapidly as it reproduces. This means that it can evade the
immunity that its ‘host’ has acquired from previous infections. The host’s
immune system does not recognise the new virus’s surface.
The natural reservoir of the influenza A virus is water
birds and wildfowl. In the wild, where ducks, geese, etc, are thinly spread, the
virus tends to cause mild disease – it would soon die out if it killed its
hosts. But where there is an abundance of birds in one place, the virus can
change to become a killer – the faster it reproduces the more successful it is
and there are plenty of hosts to replace those it kills. Industrial-scale
poultry farming provides ideal conditions for this to occur, with birds in
crowded conditions also suffering stress, lowering their immunity. Some attempts
have been made to blame wild birds for the current outbreak, but migrating birds
monitored in Thailand were free of the virus. Wild birds have been affected only
where poultry outbreaks have occurred.
Although a bird virus may infect humans, unless it changes
so that it can move from human to human, its threat is limited. But if anyone
already has human flu when they become infected with bird flu, the viruses can
reassort (mix) their genetic material. This could result in a virus able to
transmit between humans, evading all immunity humans have from previous flu
infections or vaccinations.
Experts predict that it is a matter of time before a
pandemic occurs on the scale of 1918-19. (There were less severe epidemics in
1957 and 1968.) In the advanced industrialised countries it would cause 57-132
million doctor visits, 1-2.3 million hospital admissions, and 280,000-650,000
deaths over less than two years. In poor countries with few health services, the
situation would be far worse.
Socialism will never stop new strains of viruses posing
grave threats to human health. But farming practices would be geared to minimise
the risk of the rapid spread of new viruses. The resources of a publicly owned
pharmaceutical industry would also be marshalled to develop and produce the
vaccines and treatment needed. And planning of public health would ensure
preventive action, with those at risk properly protected.
|