GENEVA, Feb 1 (Reuters) - Samples from a dead Nigerian woman believed to be sub-Saharan Africa's first fatality from bird flu have arrived in Britain for testing, the World Health Organisation (WHO) said on Thursday.

Nigerian authorities on Wednesday announced that their tests showed that the 22-year-old woman from Lagos died from the H5N1 virus after defeathering and preparing an infected chicken.

WHO spokesman Gregory Hartl said the Nigerian samples would be tested at a WHO collaborating centre in north London. The United Nations health agency seeks confirmation of preliminary testing from one of its network of laboratories.

Nigeria, Africa's most populous nation, was the first on the continent to detect the H5N1 virus in poultry. The virus has spread to 17 of Nigeria's 36 states over the past year despite measures such as culling, quarantine and bans on transporting live poultry.

In Africa, 11 people have died in Egypt from bird flu since 2003 and there has been a single non-fatal human case in Djibouti, in the eastern Horn.

Worldwide, there have been 270 confirmed bird flu cases with 164 deaths since 2003, according to the WHO.

Experts fear the virus could spark a deadly pandemic if it mutates into a form that passes easily from person to person.

"The samples are in London...Getting an accurate result will also depend on the quality of the sample," said the WHO's Hartl.

Contacts of the woman, who died on January 16, had shown no symptoms of avian influenza infection, the WHO said in a statement issued overnight.

"Samples have been tested from these contacts as well as from three other suspected cases, including one fatal case, and have all been negative in preliminary tests," it added. These samples had also been sent to the WHO reference lab in London.

The woman's mother -- who handled the same infected bird -- died on Jan. 4 with "similar symptoms", but no samples had been taken from her, according to the WHO.

Poultry meat is safe to consume when cooked thoroughly at temperatures at above 70 degrees Celsius (158F) until none of the meat is red, it said.

The greatest risk of exposure to the deadly virus is through the handling and slaughter of live infected poultry.

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