HONG KONG - The discovery of chickens infected by the bird flu virus but showing no symptoms of the disease has triggered concern over consumption of their eggs.
Scientists cannot agree whether the content of the eggs from such chickens are free of the virus, but they do say there is some risk because the surface of the egg shells may still be tainted with virus-laden excreta of the birds.
Birds infected with H5N1 shed huge amounts of the virus in their droppings and respiratory secretions, which help spread the bug over wide geographical areas.
"It is not entirely clear if the eggs of infected chickens will be affected. But if the chicken is infected, some amount of virus could be on the shell of the egg," said Samson Wong, a microbiologist at the University of Hong Kong.
Some 120 people have been infected with virus since it resurfaced in Asia in 2003, most of them due to contact with sick chickens. More than 60 people have died from the virus, which made its first jump to humans in 1997 in Hong Kong.
While some of those infected fell ill after eating sick chickens, doctors cannot quite determine if they were due to consuming or handling the birds.
Doctors have long said chicken is safe to eat as long it is thoroughly cooked. But the safety of eggs had not been in the spotlight because chickens die within 24 hours of becoming infected, too short a time window for them to produce eggs.
But the question about whether eggs are safe has assumed urgency since healthy chickens carrying the virus were discovered in Indonesia recently. The birds do not fall sick and continue laying eggs even though they carry and shed the virus.
Health experts are extremely concerned about infected birds and poultry which don't show any symptoms because they render the virus so much harder to detect and control. Some have warned against eating raw or even runny eggs, which are popular in some parts of Asia such as Japan.
SAFE?
Australia's veterinary emergency plan of 2004, a copy of which was obtained by Reuters, said that while severely affected birds will stop laying, eggs laid in the early phase of an outbreak could still contain avian influenza viruses in the albumen and yolk, as well as on the surface of the egg.
However, Guan Yi, a leading virologist from the University of Hong Kong who has studied the H5N1 virus extensively since 1997, said the eggs of chickens which tested positive for the virus were infected on the surface of their shells, and not inside.
"These chickens can continue to lay eggs and there could be contamination outside the shell from the faeces," Guan said.
Guan said asymptomatic chickens, or birds that do not fall ill or die but do carry the virus, were a result of improper use of vaccines.
In recent years, many countries in Asia have tried to get rid of H5N1 by vaccinating poultry flocks. But some vaccines used are of low quality and, instead of killing the virus, they have masked the disease.
"Many countries use vaccines and think the virus is completely exterminated ... but this problem is still in southeast Asia. It's even in migratory birds and they are dying. Why? Because the virus has gone from poultry to migratory birds, which are taking it further afield," Guan said.
Singapore last year banned imports of poultry products from Malaysia after an outbreak of bird flu near its neighbour's northern border, leading to a shortage of eggs in the city-state.
But health experts said eating eggs is still safe, as long as they are handled and cooked thoroughly until the yolk is hard.
"For such eggs, if they are kept in cold, dry storage for half to one month, they may still be used, because that would kill the virus. Or you wash the egg," Guan said.
