Cancer is often caused by the "bad luck" of random mutations that arise when cells divide, not family history or environmental causes, U.S. researchers said Thursday.

The study in the January 2 edition of the journal Science was led by researchers at Johns Hopkins University and based on a statistical model that includes many types of cancer in a range of human tissues.

An Italian doctor who contracted Ebola in west Africa has recovered from the disease after undergoing experimental treatment, local media reported on Thursday.

The 50-year-old from Sicily, who has not been named, has been in isolation at Rome's Spallanzani institute since he was evacuated from Sierra Leone in mid-November.

The International Monetary Fund is under mounting pressure to cancel the debts of the three poor West African countries hit hardest by Ebola, as their economies stall under the fallout from the disease.

The calls for a debt alleviation for Guinea, Liberia and Sierra Leone are coming not only from anti-poverty organizations.

Hong Kong culled thousands of chickens Wednesday after the potentially deadly H7N9 bird flu virus was discovered in poultry imported from China, days after a woman was admitted to hospital with the disease.

Authorities found the virus in samples taken from 120 chickens imported from the nearby Chinese city of Huizhou and slaughtered nearly 19,000 birds, including 11,800 chickens.

Most Australian states and territories are set to ban commercial sunbeds from Thursday, in a crackdown on artificial tanning in a country that has one of the highest rates of skin cancer in the world.

The ban -- which comes into force in the states of New South Wales, Victoria, South Australia, Tasmania, Queensland and in the Australian Capital Territory on January 1 -- will make Australia the second nation after Brazil to impose such a restriction, campaigners said.

Insect-eating bats that inhabited a hollow tree in a remote village in Guinea may have been the source of the world's biggest Ebola epidemic, scientists said on Tuesday.

More than 20,000 cases of Ebola, with at least 7,800 deaths, have been recorded by the World Health Organization (WHO) since a two-year-old boy died in the village of Meliandou in December 2013.

A Christmas lockdown in northern Sierra Leone aimed at preventing new Ebola infections in the country with the world's most cases ended on Monday.

The authorities did not make any official assessment but promised a statement by the end of the week.

A volunteer nurse who contracted Ebola while working in Sierra Leone was airlifted from Scotland to a specialist clinic in London on Tuesday.

A Royal Air Force ambulance was seen entering the Royal Free Hospital, where British nurse William Pooley was also treated for the disease this year.

Japan on Tuesday ordered the slaughter of some 37,000 chickens as officials announced the third bird flu outbreak in less than a month and pledged "all necessary measures" to contain the spread.

Tests confirmed the H5 strain of the virus at a farm in Yamaguchi prefecture on the southwestern tip of Japan's main Honshu island after its owner reported late Monday that several chickens had died suddenly, the farm ministry said.

A healthcare worker recently returned from Sierra Leone was on Monday diagnosed with Ebola by doctors in Glasgow in the first diagnosis of the virus in Britain during the current outbreak.

"A confirmed case of Ebola has been diagnosed in Glasgow," the Scottish government said in a press release.