Q What is a virus?

A Viruses are microscopic biological parasites that lack the ability to survive and reproduce outside living organisms, which include animals, humans and even bacteria.

They become active only when they come into contact with living cells, which they then try to hijack to produce more viruses.

Q What are coronaviruses?

A They belong to a large group of viruses that usually infect only animals, and are so named for the crown-like spikes on their surface.

Scientists have identified coronaviruses that affect humans, with seven types of these viruses classified to date.

Four of these typically cause mild to moderate upper respiratory tract illnesses such as the common cold. But the remaining three have more severe repercussions on human health.

The first is the Sars (severe acute respiratory syndrome) coronavirus, which killed almost 800 people in 32 countries 17 years ago.

The other two are Mers-CoV (Middle East respiratory syndrome coronavirus), which was first reported in Saudi Arabia in 2012 and later spread farther, and 2019-nCov (Wuhan virus), which killed its first victims in the Chinese city of Wuhan.

Q How did the Wuhan virus jump from infecting animals to humans?

A Scientists speculate that the Wuhan virus, like the Mers and Sars viruses, evolved from coronavirus strains that previously affected only animals.

Coronaviruses generally have a single strand of genetic material called RNA, which is more easily copied or mutated than humans' double-stranded DNA, and this accounts for their virality.

The Wuhan virus has been closely linked to Huanan Seafood Market in Wuhan, which reportedly also peddled live animals like deer and animal parts, in addition to seafood.

Scientists said that such unnatural situations, where animals are brought together and often housed in poor conditions in close proximity to people, create opportunities for a virus to hop between animals. The virus could then have mutated so that it is able to infect humans, and eventually start spreading among people.

Every virus typically infects a certain type of living host organism, said Dr Sebastian Maurer-Stroh, deputy executive director of research at the Agency for Science, Technology and Research's (A*Star) Bioinformatics Institute. "Viruses can shift their host preference through mutations... Some viruses mutate much faster."

Q How might the Wuhan virus spread between people?

A The Wuhan coronavirus is understood to spread much like the common flu does - through the air when an infected person coughs, through close contact such as shaking hands with an infected person, or touching an object which has the virus on it before touching one's mouth and eyes.

For now, virologists say the Wuhan coronavirus is likely not as infectious as the Sars virus. But there are concerns that the Wuhan virus' current reported 2 per cent death rate - where two out of 100 infected people die - is not representative, and that the virus could further mutate to become more lethal.

There are worries that the number of infections is under-reported, with many brushing off symptoms as those of the common flu.

Q How is the Wuhan virus different from the Sars virus?

A It is a different strain and, for now, has reported a lower fatality rate than the Sars virus.

The World Health Organisation estimates the overall fatality rate for Sars patients to be between 14 per cent and 15 per cent, while that for Wuhan is currently at 2 per cent.

Researchers have said that the Wuhan virus shares only 76 per cent of its genetic material with the Sars virus - a big difference in genetic terms, much like "comparing a dog and a cat".

There is, however, speculation that both viruses originated from bats. Recent reports have also suggested that the Wuhan virus might be linked to snakes too.

Q Should I panic?

A No, said Professor Paul Tambyah of the Department of Medicine at the National University of Singapore's Yong Loo Lin School of Medicine.

Instead, we should be concerned.

He said there are measures in place to control the outbreak here and elsewhere. The public should be concerned and thus be vigilant about maintaining good hand hygiene, seeking medical attention if unwell and staying home, he said.

Q Should I wear a mask?

A Wear a surgical mask when you have a cold or flu.

Some doctors have been wearing surgical masks as a precautionary measure at work, so some people have wondered if they should dig out their N95 masks too.

But there is no need to, said Professor Leo Yee Sin, executive director of the National Centre for Infectious Diseases. Instead, they should wear surgical ones.

"N95 masks are... very difficult to breathe in. If you find the N95 mask easy to breathe in and comfortable, you are wearing it wrongly and it is no use," she said, adding that these masks are not recommended for the public.

Dr Leong Hoe Nam, an infectious disease specialist at Mount Elizabeth Novena Hospital, said everyone with respiratory symptoms must wear masks, now that there is human-to-human transmission for the Wuhan virus.

Q Can I still visit China?

A The Ministry of Health (MOH) on Thursday said Singaporeans should avoid travelling to Wuhan, stepping up a notch from its advice on Wednesday for people to defer non-essential travel there.

The ministry said it updated the travel advisory "in view of the developing novel coronavirus situation in Wuhan and other parts of China", with confirmed cases spreading beyond Wuhan to Beijing, Shanghai, Tianjin and Guangdong, which abuts densely populated Hong Kong.

It also cited the travel halt imposed by the Chinese authorities on Thursday, as all flights out of the city were cancelled and trains, buses and ferries suspended.

The ministry also reminded the public to continue to exercise caution and pay attention to personal hygiene when travelling to the rest of China.

MOH said all travellers should monitor their health closely for two weeks upon return to Singapore and seek medical attention promptly if they feel unwell, and also inform their doctor of their travel history.

If they have a fever or respiratory symptoms such as a cough or runny nose, they should wear a mask and call the clinic ahead of the visit.

Q Should I be worried about China tourists coming into Singapore?

A Singapore is stepping up precautionary measures in anticipation of more travellers in the lead-up to the Chinese New Year holidays.

The expanded measures include temperature screening for all travellers arriving from China - not just Wuhan alone - at Changi Airport from yesterday, and issuing health advisory notices to them.

Q Should I get a flu jab?

A A flu vaccine will not help protect you against the Wuhan coronavirus. There is no vaccine to protect against coronaviruses.

However, according to an advisory from Raffles Medical, you should still get a flu jab if you are travelling to places where there are suspected cases to prevent you from contracting influenza symptoms that may mislead the screening authorities at temperature checkpoints.

There is also no specific treatment to cure illnesses caused by human coronaviruses, including pneumonia caused by the Wuhan virus.

Patients typically recover on their own after some time.