* WHO concerned about possible bird flu human carriers * U.N. body to test if cases exist * Worries about mutation of the pathogenic virus
By Cynthia Johnston
CAIRO, April 8 (Reuters) - The World Health Organisation is concerned some Egyptians may carry the highly pathogenic bird flu virus without showing symptoms, which could give it more of a chance to mutate to a strain that spreads easily among humans.
Whether such cases exist still has to be put to the test and will be the focus of a planned Egyptian government study backed by the global health body, said John Jabbour, a Cairo-based emerging diseases specialist at WHO.
"This is a concern only, now. It is a question to be asked," Jabbour told Reuters. He said a change in the pattern of human bird flu infections this year in Egypt had raised concerns about the existence of so-called sub clinical cases.
The most populous Arab country, which has been hit harder by bird flu than any other country outside of Asia, has seen a surge in infections this year.
While the H5N1 virus only rarely infects people, experts fear it could mutate into a form that humans could easily pass to one another, sparking a pandemic that could kill millions.
The emergence of symptomless human carriers of the virus would be a worrisome development because it could allow the virus, undetected and untreated, more time to mutate inside the human body, Jabbour said.
"If there is any sub clinical case in Egypt, the aim is to treat immediately to stop the reproduction of the virus. Because whether (through) mutation or reassortment, this will lead to the pandemic strain," he said.
Of the 11 Egyptians infected with bird flu this year, all but two have been children under age three while adult cases have all but dried up. All have survived.
That is starkly different from the same period a year ago, when seven people -- mostly adults and older children -- contracted the virus and three died.
'SOMETHING STRANGE HAPPENING'
Jabbour said the rise in infections in children without similar cases among adults had triggered questions as to whether adults were being infected with the virus but not falling ill.
"There is something strange happening in Egypt. Why in children now and not in adults?" he said. "We need to see if there are sub clinical cases in the community."
Jabbour said there had been no known instances of sub clinical bird flu cases in humans in other countries where the disease was present. Some birds, like ducks, are known to carry and spread the virus without showing symptoms, he said.
The Egyptian study, which Jabbour said should begin in the coming months, would test the blood of people who may have been in contact with infected birds but had not become sick.
Since 2003 the avian influenza virus has infected more than 400 people in 15 countries and killed 256 of them. It has killed or forced the culling of more than 300 million birds across Asia, the Middle East, Africa and Europe.
Some 23 Egyptians have died after contracting the virus, most after contact with infected domestic birds in the country where roughly 5 million households depend on domestically raised poultry as a major source of food and income.
But Jabbour said there was still no evidence of the disease being passed from person to person in Egypt.
He added that two toddlers from the northern province of Beheira infected within days of one another in March were cousins. But he said the boys were believed to have contracted the virus from the same sick birds, not from each other.
"There is no change in the virus at all in the virus strain in Egypt. It is the same since the beginning of the outbreak. There is no mutation, nothing," he said. (Writing by Cynthia Johnston)