NEWS - Bird flu experts question advice on eating poultry

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Nature 440, 850-851 (13 April 2006)

Bird-flu experts question advice on eating poultry

How safe are chicken and eggs?

Can people catch the H5N1 avian flu virus from eating infected poultry?

Colin Blakemore, chief executive of the UK Medical Research Council, says

the public need not worry. " There is no evidence of transmission to people

by eating cooked eggs or chicken, " he said on BBC radio last week, adding

that the only food risk he could see was from " drinking swans' blood " .

Blakemore's sound bite came a day after Britain's first case of H5N1 in a

wild bird was confirmed - a dead swan found floating in a harbour in

Cellardyke, Scotland. And it echoes a slew of recent reassurances by

governments worldwide and by the World Health Organization (WHO), all

conscious of damaging public confidence and the poultry industry.

But many flu scientists are concerned that, although the risks are low

compared with those associated with contact with diseased birds, there is

not enough evidence to say that the virus cannot be transmitted by eating

infected poultry. " Oral transmission is an open question, " says Masato

Tashiro, a virologist at the National Institute of Infectious Diseases in

Tokyo. " Direct evidence of oral infection is lacking, but so too is proof

against. "

On 23 March, the European Food Safety Authority (EFSA) published a prominent

scientific risk assessment (EFSA J. 74, 1-29; 2006). Its advice is that

poultry products are safe to eat and have " not been implicated in the

transmission of the H5N1 avian influenza virus to humans " .

H5N1 is present in the meat and eggs of infected birds, and animals have

become infected by eating diseased birds. But the EFSA plays down this route

in humans, arguing that " humans who have acquired the infection have been in

direct contact with infected live or dead birds " .

That overstates the case, says Jody Lanard, a physician and

risk-communication consultant based in Princeton, New Jersey, who has

recently advised the WHO about pandemic communication. She points out that

the report itself acknowledges elsewhere that in many instances there is not

enough epidemiological evidence to identify the source of infection, and

that poor preparation and cooking of food cannot be excluded as the cause.

" Such cases could equally well indicate a likely gastro-intestinal portal of

entry, " agrees Menno de Jong, a virologist at the Hospital for Tropical

Diseases in Ho Chi Minh City, Vietnam.

The report also dismisses the idea that H5N1 can enter the body via the

human gut, concluding that there is " no proof that virus replicates in the

human intestine " . Although it mentions the presence of diarrhoea in infected

humans, together with the detection of viral RNA in intestines and the virus

in rectal swabs, it says these " do not allow one to conclude that the GI

tract is a portal of entry or a target organ " .

De Jong, who has treated many of the cited diarrhoea cases, says the

report's authors are " formally right " to say there is no proof that the

virus replicates in the intestine. But there is no proof that it doesn't

either, he says, noting that some of the diarrhoea cases had no respiratory

symptoms.

" Available evidence suggests that the gastrointestinal tract in humans is a

portal of entry for H5N1, " agrees Albert Osterhaus, a virologist at the

Erasmus Medical Center in Rotterdam. He carried out a recent study in which

cats became infected with H5N1 after being fed infected chickens (T. Kuiken

et al. Nature 440, 741-742; 2006) - evidence also dismissed by the EFSA

report as " unproven " .

Of course, to pose a risk the virus must enter the human food chain. The

EFSA and other authorities point out that this is unlikely, at least in

industrialized countries. But some scientists, including Osterhaus, say it

cannot be excluded - for example, if the virus enters poultry a few days

before clinical signs appear.

The final argument of the EFSA and the WHO is that even if the virus did

enter the food chain, it would be killed by cooking or pasteurization, in

the same way as bacterial pathogens such as Salmonella. But Lanard points to

the countless infections with Salmonella worldwide, and complains that most

risk assessments fail to acknowledge that in reality few people follow

guidelines for the safe handling and cooking of poultry. These involve

cooking chicken right through to 70 °C and eggs until they are hard, using

separate knives and chopping boards for raw and cooked foods, and

hand-washing between operations.

An EFSA spokesperson says the agency stands by the report's conclusions.

Several scientists are also convinced that avian flu carries no food risks.

" Avian influenza has never been and should never have been seen as a food

safety issue, " says Les Sims, a consultant for the UN's Food and Agriculture

Organization (FAO). Bird-flu concerns over food, he says, " have a

devastating impact on the livelihood of millions of farmers globally and

demonstrate that risk communication on this has been a total failure " .

But Lanard maintains that to say bird flu is not a food issue is an

" overstatement " . She says that such advice shows that little has been learnt

about risk communication since the British agriculture minister publicly fed

his young daughter a hamburger at the height of the crisis over bovine

spongiform encephalitis. A 2005 European Commission poll showed that almost

half of European citizens believe authorities favour economic interests over

consumer health, she points out. " These over-reassuring statements discount

the future - they are set up for public distrust, " she says. " Although there

is no direct evidence that transmission can occur through poorly cooked

infected poultry, all animal evidence to date unfortunately suggests that

this is possible. "

http://www.nature.com/nature/journal/v440/n7086/full/440850a.html

Not an MD

I'll tell you where to go!

Mayo Clinic in Rochester

http://www.mayoclinic.org/rochester

s Hopkins Medicine

http://www.hopkinsmedicine.org