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In a letter to The Lancet, Wickramasinghe explains that a small amount of a virus introduced into the stratosphere could make a first tentative fallout east of the great mountain range of the Himalayas, where the stratosphere is thinnest, followed by sporadic deposits in neighboring areas. Could this explain why new strains of the influenza virus that are capable of engendering epidemics, and which are caused by radical genetic mutations, usually originate in Asia? Wickramasinghe argues that if the virus is only minimally infective, the subsequent course of its global progress will depend on stratospheric transport and mixing, leading to a fallout continuing seasonally over a few years; even if all reasonable attempts are made to contain an infective spread, the appearance of new foci almost anywhere is a possibility.

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In Vietnam, the outbreak of avian influenza's subtype of H5N6 started on 18 January and infected and killed more than 2,000 birds in the country's north. Additionally, 300 birds were killed and disposed of, the OIE said, citing Dr. Dong Pham Van, the head of the Agriculture Ministry's department of animal health.

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Asia steps up defences as China confirms sixth coronavirus death

Nations increase fever checks at airports amid fears of a bigger outbreak of the virus that causes pneumonia.

Asian countries have ramped up measures to block the spread of a new virus as the death toll in China rose to six and the number of cases jumped to almost 300, raising concerns in the middle of a major holiday travel rush.

From Australia to Thailand and as far as Nepal, nations stepped up fever checks of passengers at airports to detect the Severe Acute Respiratory Syndrome (SARS)-like coronavirus, which first emerged in the central Chinese city of Wuhan.

Footage from Twitter reportedly shows checks occurring on aircraft in Wuhan: "[A scary sentence] I just returned from Wuhan!"

Zhou Xianwang, mayor of Wuhan, told state broadcaster CCTV on Tuesday that the death toll had risen from four to six.

Fears of a bigger outbreak increased after a prominent expert from China's National Health Commission confirmed late on Monday that the virus can be passed between people.

Zhong Nanshan, head of the National Health Commission, said there was no danger of a repeat of 2002's SARS epidemic that killed nearly 800 people across the world, as long as precautions were taken.

"It took only two weeks to identify the novel coronavirus," state news agency Xinhua quoted Zhong as saying late on Monday.

Earlier, Zhong acknowledged patients may have contracted the new virus without having visited the central city of Wuhan where the infection is thought to have originated in a seafood market.

"Currently, it can be said it is affirmative that there is the phenomenon of human-to-human transmission," he said in an interview with state broadcaster CCTV.

China said it would attend a special World Health Organization (WHO) meeting on Wednesday which will determine whether to declare a rare global public health emergency over the disease, which was detected in Thailand, Japan and South Korea among four people who had visited Wuhan.

Outbreak spreads

Almost 80 new cases have been confirmed, bringing the total number of people hit by the virus in China to 291, with the vast majority in Hubei, the province where Wuhan lies, and others in Beijing, Shanghai and Guangdong, according to the National Health Commission.

State media said one case was found in Zhejiang province.

Australia on Tuesday said it would screen passengers on flights from Wuhan amid rising concerns that the virus will spread globally as Chinese travellers take flights abroad for the Lunar New Year holiday that starts this week.

A man showing symptoms of the new disease who had travelled to Wuhan was in isolation as health officials awaited test results, public broadcaster ABC reported on Tuesday

"The outbreak could perhaps not have come at a worse time," said Al Jazeera's Katrina Wu, who is in Beijing.

"This is the peak travel season in China. The government has always boasted that during the Lunar New Year you see two to three billion trips being made across the country and Wuhan is not a small city; it's about 11 million people who will be travelling not only in China, but overseas. It's a major transport hub."

Authorities around the globe, including in the United States and many Asian countries, have stepped up the screening of travellers from Wuhan.

Zhong, the head of the National Health Commission, said two people in Guangdong province in southern China caught the disease from family members who had visited Wuhan.

He added that 14 medical staff helping with coronavirus patients had also been infected.

The Wuhan virus causes a type of pneumonia and belongs to the same family of coronaviruses as SARS. Symptoms include fever and difficulty in breathing, which are similar to many other respiratory diseases and pose complications for screening efforts.

SARS originated in southern China in 2002 and spread to 26 countries across the world over the following months, infecting more than 8,000 people before it was brought under control, according to the World Health Organization (WHO).

The WHO, which is due to hold an emergency meeting on the outbreak on Wednesday, has said an animal source appeared most likely to be the primary origin of the Wuhan outbreak

Enhanced screening

South Korea on Monday reported its first case of the new coronavirus - a 35-year-old woman who had flown in from Wuhan.

Thailand and Japan previously confirmed a total of three cases - all of whom had visited the Chinese city.

© Aly Song/ReutersThe outbreak is spreading as China gears up for the Lunar New Year festival when hundreds of thousands of people visit family or take holidays

WHO has said the jump in new cases was the result of "increased searching and testing for [the virus] among people sick with respiratory illness".

Wuhan authorities said they have installed infrared thermometers at airports, and railway and coach stations across the city. Passengers with fever were being registered, given masks and taken to medical institutions.

Chinese state media moved to calm the mood as discussion swelled on social media about the coronavirus spreading to other Chinese cities.

Weighing in on the matter for the first time, China's President Xi Jinping said on Monday that safeguarding people's lives should be given "top priority" and that the spread of the epidemic "should be resolutely contained", according to CCTV.

Xi said it was necessary to "release information on the epidemic in a timely manner and deepen international cooperation", and ensure people have a "stable and peaceful Spring Festival", the broadcaster said.

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