TORONTO -- On New Year’s Eve, the World Health Organization received an unusual message.

Cases of a mysterious illness of unknown origins with pneumonia-like symptoms were reported in Wuhan, a densely-populated city in central China with more than 11 million people.

Four weeks later, the newly-identified coronavirus has spread to 18 countries, infected more than 6,000 people and killed 132. Screening measures have been implemented in airports across the world, but there are doubts that such measures are helping stall the outbreak.

In Canada, two cases have been confirmed in Toronto and a presumed positive case is under investigation in British Columbia. So far, no Canadians have died.

With new information emerging each day, here’s what we know so far about the outbreak.

WHAT IS A CORONAVIRUS?

The new illness, described by the World Health Organization as a novel coronavirus, falls under a larger family of coronaviruses. First identified in humans in the mid-1960s, coronaviruses are zoonotic, which means they can be transmitted between animals and people.

Coronaviruses can be as minor as the common cold or life-threatening, as was the case with SARS.

The term gets its name from the Latin word “corona,” meaning halo or crown, which is what the virus looks when viewed through an electron microscope.

Symptoms of coronaviruses range from mild symptoms, such as coughing and sneezing, to more serious symptoms, such as shortness of breath, body aches and chills.

HOW IS THIS ONE DIFFERENT?

Scientists in China identified the new coronavirus on Jan. 7, eight days after it was first reported. They were also able to identify the genetic sequence of the virus and shared it with the international community – a sign of transparency praised by the World Health Organization.

Primary symptoms of the new coronavirus include fever, cough, tightness of the chest and shortness of breath.

Despite being sequenced, the source of the virus has not been found, and new information continues to emerge regularly about its severity and spread.

Studies have suggested that bats and snakes may be related to the outbreak. Genetic analysis of the virus published in the journal Science China Life Sciences found a striking resemblance to a virus that exists in bats.

Separate analysis published in the Journal of Medical Virology suggested that snakes were “the most probable wildlife animal reservoir.”

HOW IS IT SPREAD?

The virus was initially linked to a handful of people in Wuhan, many of whom worked at a seafood market. Scientists said they believed the illness was related to contact with animals and could not be spread from human to human.

But that changed when the head of a Chinese government expert team confirmed cases passed from one person to another. Health-care workers have since tested positive for the virus and, in Japan, a bus driver who hadn’t been to China but drove tourists from Wuhan fell ill.

How easily the virus can be spread from one person to the next remains unclear.

Doubts have been raised about whether or not China is being forthcoming about numbers. A report by Imperial College London estimates that 1,723 people could have been infected by Jan. 12 -- nearly nine times higher than China’s figure at the time.

IS IT SIMILAR TO SARS?

The coronavirus has been compared to SARS, and the two illnesses do share some similarities.

SARS is considered a coronavirus, and it also began in China. Back in 2002, China withheld key information about how widely SARS had spread and the severity of the problem. More than 8,000 people were killed worldwide, including 44 in Canada.

However, in this case, early lab tests have ruled out a resurgence of SARS and its close cousin, Middle East respiratory syndrome (MERS).

WHERE HAS THE CORONAVIRUS SPREAD?

The virus was discovered in Wuhan but has since spread across China and around the world. The federal government says Canadians should avoid all travel to Hubei province, where Wuhan is located.

Countries with confirmed cases of the novel coronavirus include:

  • China
  • Canada
  • United States
  • Hong Kong
  • Japan
  • Macau
  • Taiwan
  • Australia
  • Cambodia
  • France
  • Germany
  • Malaysia
  • Nepal
  • Sri Lanka
  • Singapore
  • Thailand
  • South Korea
  • Vietnam
  • United Arab Emirates

WHAT IS HAPPENING AT CANADIAN AIRPORTS?

Airports in Toronto, Montreal and Vancouver have added electronic notifications for travellers asking anyone who has been to Wuhan and is experiencing flu-like symptoms to contact a border services agent.

Electronic kiosks at the three airports have also added an additional health screening question about the new virus.

Unlike authorities at U.S. airports, Canadian officials are not using thermal scanners to test for the virus. Questions have been raised about the effectiveness of airport screening because travellers infected with the virus may not be showing symptoms at the time of travel.

HOW IS INTERNATIONAL AIR TRAVEL AFFECTED?

Several international airlines have altered or outright suspended flights to and from China, including Air Canada.

Air Canada, which run 33 flights each week to China, is cancelling select flights to China. The airline says the reduction is relatively small, and that affected customers will be notified.

British Airways has halted all flights to China, and American Airlines suspended flights to and from Shanghai and Beijing.

Britain’s Foreign Office has advised against all but essential travel to mainland China, and American Airlines cited a significant decline in demand for its decision to cancel flights.

Air India, Seoul Air and Lion Air have halted all flights to China. Service changes have also been made at Finnair, Cathay Pacific and Jetstar Asia.

WHAT IS THE RISK TO CANADIANS?

Canadian health authorities have repeatedly described the risk of the coronavirus spread as low. Dr. Theresa Tam, Canada’s chief public health officer, called the outbreak “a rapidly evolving situation” but said that, for the moment, there is no cause for alarm.

"Although we now have a case in Canada, the risk to Canadians remains low," she said on Jan. 26, one day after the first Canadian case was confirmed.

Tam added that more Canadian cases of coronavirus would not be unexpected given global travel patterns.