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.

U.S. authorities have given emergency authorization to Swiss pharmaceutical firm Roche for an Ebola test that can take as little as three hours, the company said on Monday.

The U.S. Food and Drug Administration authorized the test for emergency use on patients with signs and symptoms of the deadly virus, Roche said.

Egyptian health authorities on Monday reported the country's 10th death this year from bird flu, as well as the first case of H5N1 infection in the capital.

The death occurred last week in the southern province of Aswan, health ministry spokesman Hossam Abdel Ghaffar said.

West Africa's fight to contain Ebola has hampered the campaign against malaria, a preventable and treatable disease that is claiming many thousands more lives than the dreaded virus.

In Gueckedou, near the village where Ebola first started killing people in Guinea's tropical southern forests a year ago, doctors say they have had to stop pricking fingers to do blood tests for malaria.

China has dismissed eight officials after pork from pigs infected with a "highly contagious virus" was found to have entered the market, state media said Monday.

The country's latest food scandal was revealed in an investigation by state broadcaster China Central Television which said the annual revenue of the tainted pork was more than 20 million yuan ($3.2 million).

A man has died from the H7N9 bird flu strain in eastern China, state media reported Monday, at the end of a year in which cases of the virus have accelerated.

The deceased man was one of two recent cases reported in the city of Yongkang in Zhejiang. They were the third and fourth in the province "since the start of winter", the China News Service reported.