Her warning came in her closing address to the 66th World Health Assembly (WHA) in Geneva on Monday. And, as if to underline the singificance of her words, on Tuesday, Saudi Arabia reported that five more people have been infected with the virus, bringing the unofficial total number of people infected in the country to 37, with 18 deaths.
CDC scientists are becoming frustrated at the delays in getting samples of MERS-CoV. Experts know very little about this virus - they have no idea where it lives and how people contract it .
Adding these new cases to the figures issued early Tuesday by the US Centers for Disease Control and Prevention (CDC), brings the unofficial global case count to 49, with 24 deaths, distributed as follows:
France 2 cases (1 death); Jordan 2 (2); Qatar 2 (0); Saudi Arabia 37 (18); Tunisia 2 (0); UK 3 (2); and UAE 1 (1).
Update: June 17th, 2013 - Saudi Arabia announced four more deaths from MERS-CoV infection, bringing the death toll in the country to 32. Thirty-seven people have died from MERS-CoV infection worldwide.
New CoronavirusFirst identified in the 1960s, coronaviruses are a large family of viruses, common throughout the world, that can infect people and animals. They are so called because of the crown-like projections on their surfaces.
Five different coronaviruses can infect humans and cause illnesses. Mostly these are mild to moderate upper-respiratory infections like the common cold.
But some coronaviruses cause much more severe illness, such as the one behind the 2002 SARS (severe acute respiratory syndrome) outbreak that spread from Hong Kong around the world, killing around 800 people.
Like all viruses, coronaviruses cause infection by invading host cells and taking over their processes to make virus particles instead. But exactly how this happens in the case of coronaviruses is not well understood.
A study published in PLoS Pathogens in 2008 went some way toward understanding the replication process of the coronavirus.
However, this new MERS coronavirus is genetically quite distinct from SARS, according to information published on the WHO website in September 2012.
The name Middle East respiratory syndrome coronavirus (MERS-CoV) was put forward by the Coronavirus Study Group of the International Committee on Taxonomy of Viruses and is the result of widespread consultation with scientists, says WHO.
The international agency has accepted the new name despite normally not being in favour of having geographic designations in virus names.
Chan Concerned About Fast Emerging DiseaseChan sounded the alarm on the global threat posed by MERS as she closed an intensive seven-day international meeting that had agreed new public health measures and recommendations aimed at securing greater health benefits for all people, everywhere.
However, Chan said as she surveyed the overall global situation, "my greatest concern right now is the novel coronavirus".
She is concerned that we "understand too little" about the virus, when viewed against the size of its potential threat.
"Any new disease that is emerging faster than our understanding is never under control," Chan explained.
"These are alarm bells and we must respond. The novel coronavirus is not a problem that any single affected country can keep to itself or manage all by itself. The novel coronavirus is a threat to the entire world," she warned.
WHO Team to Help Saudi Arabia Assess MER Risks Ahead of the Annual HajThe new cases in Saudi Arabia appear to be older people who are not in good health.
A brief statement from the Saudi Ministry of Health says "... five novel Coronavirus cases have been recorded among citizens in the Eastern Region, ranging in age from 73 to 85 years, but they have all chronic diseases".
According to an article in Arab News on 25 May, the WHO is sending a second team to Saudi Arabia to help investigate the new virus.
The source of the outbreak is still not known, but as cases have appeared in clusters it suggests the virus is spreading from person to person.
Chan told Arab News that they need to do a proper risk assessment to get some clarity "on the incubation period, on the signs and symptoms of the disease, on the proper clinical management and then, last but not least, on travel advice".
The UN agency, which sent a first team to Saudi Arabia earlier in May, says it will provide a fresh assessment ahead of the annual Haj that is due to take place in the Kingdom in October.
Haj is the single largest gathering of human beings on the planet. In 2012, it attracted over 3 million pilgrims from 189 countries.