A never-before-seen virus detected in the Chinese city of Wuhan has claimed 81 lives and infected nearly 3,000 Chinese citizens with a pneumonia-like illness, according to China's National Health Commission. The virus was first reported to the World Health Organization on Dec. 31 and has been under investigation since. Chinese scientists have linked the disease to a family of viruses known as coronaviruses, which include the deadly SARS and Middle East respiratory syndrome. 

On Friday, French authorities confirmed three cases inside the country, the first known cases in Europe and Australia announced its four. On Sunday, the US Centers for Disease Control and Prevention announced a fifth case in the US, this time in Arizona. There are now more than 60 patients under investigation for possible infection in over 20 US states, according to Dr. Nancy Messonnier of the CDC. 

Scientists have yet to fully understand the destructive potential of the new virus, known as 2019-nCoV. Researchers and investigators are just beginning to figure out where it originated, how it's transmitted and how far it has spread.

As of Monday morning, confirmed case numbers had reached nearly 3,000 in China and abroad. Chinese authorities also confirmed that health workers have been infected with the virus, suggesting that human-to-human transmission is possible.

Authorities are taking steps to guard against the spread of 2019-nCoV. On Thursday, a special WHO committee decided it was still too early to declare a public health emergency on a global level. On Saturday, though, Hong Kong declared a citywide emergency, its highest warning level, canceling all official Chinese New Year celebrations and extending school breaks for the holiday until Feb. 17. Also on Saturday, China said that starting Monday it would clamp down on travel for some of its citizens heading abroad, including suspending tour groups and temporarily halting the sale of flight and hotel packages.

The situation is rapidly evolving. We've collated everything we know about the mystery virus, what's next for researchers and some of the steps you can take to reduce your risk. 

What is a coronavirus?

Coronaviruses belong to a family known as Coronaviridae, and under an electron microscope they look like spiked rings. They're named for these spikes, which form a halo around their viral envelope.

Coronaviruses contain a strand of RNA in their envelope and can't reproduce without getting inside living cells and hijacking their machinery. The spikes on the viral envelope help them bind to cells, which gives them a way in. It's like blasting the door open with C4. Once inside, they turn the cell into a virus factory, using its molecular conveyor belt to produce more viruses, which are then shipped out. The virus progeny infect other cells and the cycle starts anew.

Typically, these types of viruses are found in animals ranging from livestock to household pets to wildlife such as bats. When they make the jump to humans, they can cause fever, respiratory illness and inflammation in the lungs. In immunocompromised individuals, such as the elderly or those with HIV-AIDS, such viruses can cause severe respiratory illness.

Extremely pathogenic coronaviruses were behind SARS (severe acute respiratory syndrome) and MERS and were easily transmitted from human to human. SARS, which showed up in the early 2000s, infected more than 8,000 people and resulted in nearly 800 deaths. MERS, which appeared in the early 2010s, infected almost 2,500 people and led to more than 850 deaths.

Where did the virus come from?

The virus appears to have originated in the Huanan Seafood Wholesale Market in Wuhan, a Chinese city about 650 miles south of Beijing that has a population of more than 11 million people. The market sells fish, as well as a panoply of meat from other animals, including bats and snakes. The Wuhan market was shut down Jan. 1. 

Markets have been implicated in the origin and spread of viral diseases in past epidemics, and a large majority of the people so far confirmed to have come down with this coronavirus had been to the Huanan Seafood marketplace in recent weeks. The market seems like an integral piece of the puzzle, but researchers will need to conduct a range of experiments and tests to confirm the virus' origin.

"Testing of animals in the Wuhan area, including sampling from the markets, will provide more information," said Raina MacIntyre, a head of the biosecurity research program at the University of New South Wales' Kirby Institute.

On Wednesday, a report in the Journal of Medical Virology by a team of Chinese researchers suggested snakes were the most probable wildlife animal reservoir for 2019-nCoV. The work examined the genetic code of the virus and compared it with that of two types of snakes, the many-banded krait and the Chinese cobra. The research demonstrated that the snakes' genetic code displayed a high level of similarity with the virus. 

Shortly after, two preprint studies refuted these claims, suggesting 2019-nCoV likely originated in bats. 

"We haven't seen evidence ample enough to suggest a snake reservoir for Wuhan coronavirus (2019-nCoV)," said Peter Daszak, president of nonprofit EcoHealth Alliance, which researches the links between human and animal health.

"This work is really interesting, but when we compare the genetic sequence of this new virus with all other known coronaviruses, all of its closest relatives have origins in mammals, specifically bats. Therefore, without further details on testing of animals in the markets, it looks like we are no closer to knowing this virus' natural reservoir."

On Thursday, a group of Chinese scientists uploaded a paper to pre-print website biorXiV studied the viral genetic code and compared it to the previous SARS coronavirus and other bat coronaviruses. They discovered the genetic similarities run deep: The virus shares 80% of its genes with the previous SARS virus and 96% of its genes with bat coronaviruses. Importantly, the study also demonstrated the virus can get into and hijack cells the same way SARS did.

All good science builds off previous discoveries -- and there is still a lot to learn about the basic biology of 2019-nCoV before we have a good grasp of exactly which animal vector is responsible for transmission. 

How many confirmed cases have been reported?

Authorities have confirmed nearly 3,000 cases as of Monday. The bulk are in China, with a total of 20 cases reported in neighboring Taiwan, Hong Kong and Macau. 

Internationally, a handful of cases have been confirmed in Thailand, Japan, South Korea, Malaysia and Vietnam. In the US, five cases have been confirmed: Two in California and one each in Washington, Illinois and Arizona. Australia has seen five cases, France three. Canadian authorities announced its first "presumptive" case on Saturday, a male in his 50s who had traveled through Wuhan.

Here's the breakdown as it stands:

• China: 2,737 confirmed cases 
• Hong Kong: 8 confirmed cases
• Macau: 8 confirmed cases
• Thailand: 8 confirmed cases 
• US: 5 confirmed cases
• Australia: 5 confirmed cases
• Taiwan: 4 confirmed cases
• Japan: 4 confirmed cases
• Malaysia: 4 confirmed cases
• Singapore: 4 confirmed cases
  
• France: 3 confirmed cases
• South Korea: 3 confirmed cases
  
• Vietnam: 2 confirmed cases  
  
• Canada: 1 presumptive case
• Nepal: 1 confirmed case
  

You can track the spread of the virus with this handy online tool, which is collating data from a number of sources including the CDC, WHO and Chinese health professionals. (Note: There may be differences in our reports and the tracking tool.)

National authorities in China continue to monitor more than 1,300 residents who visited the Wuhan market or have had prolonged contact with those presenting symptoms of the disease.

The death toll stands at 81 -- 76 in Hubei and five elsewhere in China.

The first reported death in Hubei province was a 61-year-old man who'd frequented the Wuhan market and had chronic liver disease and abdominal tumors. The second was a 69-year-old man who went to a hospital with severe damage to multiple organs. 

How do we know it's a new coronavirus?

In short, science.

The Chinese Center for Disease Control and Prevention dispatched a team of scientists to Wuhan to gather information about the new disease and perform testing in patients, hoping to isolate the virus. Their work, published in the New England Journal of Medicine on Jan. 24, examined samples from three patients. Using an electron microscope, which can see in nanometers, and studying the genetic code, the team were able to visualize and genetically identify the novel coronavirus for the first time.

Understanding the genetic code helps researchers in two ways: It allows them to create tests that can identify the virus from patient samples, and it gives them potential insight into creating treatments or vaccines. 

How does the coronavirus spread?

This is one of the major questions researchers are working hard to answer. Though the first infections were potentially the result of animal-to-human transmission, it's likely that human-to-human transmission has followed.

On Monday, the University of Minnesota's Center for Infectious Disease Research and Policy reported that health workers in China had been infected with the virus. During the SARS epidemic this was a notable turning point, as health workers moving between countries spread the disease.

Chinese authorities have since confirmed that health workers have been infected with the virus, suggesting human-to-human transmission.

"The major concern is hospital outbreaks, which were seen with SARS and MERS coronaviruses," MacIntyre said. "Meticulous triage and infection control is needed to prevent these outbreaks and protect health workers."

In Wuhan, authorities are rushing to build a thousand-bed hospital to treat coronavirus patients as the province struggles with hospital bed shortages. It's aiming to open the facility on Feb. 3, giving construction workers 10 days to get it ready.

China shut down Wuhan to reduce the spread of the virus, canceling transportation leaving the city starting at 10 a.m. Thursday. The travel restrictions were extended to four other cities (Huanggang, Ezhou, Chibi and Zhijiang) later that day, and constraints were announced in eight more cities on Friday -- impacting more than 35 million people. 

The restrictions come during a busy travel period for China, when citizens typically travel for the Lunar New Year. Major public events Chinese capital Beijing have been canceled, and both Beijing's Forbidden City and Shanghai's Disneyland said they'd close from Saturday. All of the restrictions and closures will last indefinitely.

WHO convenes emergency committee

Tedros Adhanom Ghebreyesus, the director-general of the World Health Organization, convened an emergency committee on Wednesday to determine whether this new virus constitutes a public health emergency. 

"There was an excellent discussion during the committee today, but it was also clear that to proceed, we need more information," Ghebreyesus said during a press conference Wednesday. A full replay of the press conference is below.  

The emergency committee reconvened Thursday to continue to discuss the outbreak. On Thursday, the committee decided that it was still too early to declare a public health emergency.

"If WHO declares a public health emergency of international concern, it enables WHO greater powers for disease control using the International Health Regulations," MacIntyre said.

In the fall, an emergency committee met regarding the Ebola virus epidemic in the Democratic Republic of the Congo. The meeting outlined key strategies and commitments to strengthen and protect against the spread of the disease.

What are the symptoms?

The new coronavirus causes symptoms similar to those of previously identified disease-causing coronaviruses. In currently identified patients, there seems to be a spectrum of illness: A large number experience mild pneumonia-like symptoms, while others have a much more severe response.

On Jan. 24, prestigious medical journal The Lancet published an extensive analysis of the clinical features of the disease.

According to the report, patients present with:

• Fever, elevated body temperature.
• Dry cough.
  
• Fatigue or muscle pain.
• Breathing difficulties.   
  

Less common symptoms of coronavirus include:

• Coughing up mucus or blood.
• Headaches.
• Diarrhea.

As the disease progresses, patients also come down with pneumonia, which inflames the lungs and causes them to fill with fluid. This can be detected by an X-ray and was present in all 41 cases studied.

Is there a treatment for coronavirus?

Coronaviruses are notoriously hardy organisms. They're effective at hiding from the human immune system, and we haven't developed any reliable treatments or vaccines that can eradicate them. In most cases, health officials attempt to deal with the symptoms.

"There is no recognized therapeutic against coronaviruses," Mike Ryan, executive director of the WHO Health Emergencies Programme, said during the Emergency Committee press conference Wednesday. "The primary objective in an outbreak related to a coronavirus is to give adequate support of care to patients, particularly in terms of respiratory support and multi-organ support."  

That doesn't mean vaccines are an impossibility, however. Chinese scientists were able to sequence the virus' genetic code incredibly quickly, giving scientists a chance to study it and look for ways to combat the disease. According to CNN, researchers at the US National Institutes of Health are already working on a vaccine, though it could be a year or more away from release.

Notably, SARS, which infected around 8,000 people and killed around 800, seemed to run its course and then mostly disappear. It wasn't a vaccine that turned the tide on the disease but rather effective communication between nations and a range of tools that helped track the disease and its spread.

"We learnt that epidemics can be controlled without drugs or vaccines, using enhanced surveillance, case isolation, contact tracking, PPE and infection control measures," MacIntyre said.

How to reduce your risk of coronavirus

With confirmed cases now seen in the US, Thailand, Japan, South Korea and potentially Australia, it's possible that 2019-nCoV could be spreading much further afield. The WHO recommends a range of measures to protect yourself from contracting the disease, based on good hand hygiene and good respiratory hygiene -- in much the same way you'd reduce the risk of contracting the flu.

Meanwhile, the US State Department has issued a travel advisory, urging people to "exercise increased caution in China." A warning from the CDC advises people to "avoid nonessential travel."

A Twitter thread, developed by the WHO, is below.

This story was originally published Jan. 19 and is updated frequently as new information becomes available.