The novel coronavirus has claimed 20 lives, including a patient from Abu Dhabi, but health experts have yet to determine the source of the outbreak, how it spreads - or even what it should be called.
Coronavirus: Questions over the Sars-like virus but few answers
With 20 deaths and 38 laboratory-confirmed cases, three big questions now confront the international health community as it tries to come to terms with the new coronavirus first recognised in Saudi Arabia last year.
Does this virus have the potential to turn into a Sars-like outbreak, in which an animal virus jumped species and spread quickly from human to human?
Which animal is the source? And - an entirely political consideration - what are we going to call it?
Until February 13, by which time there had been 10 confirmed cases, the World Health Organisation (WHO) seemed to be suggesting the answer to the first question was "no".
But this week, during a visit by an official to Saudi Arabia, WHO conceded that here, perhaps, was a virus capable of leaping from human to human - just like Sars.
"The different clusters seen in multiple countries increasingly support the hypothesis that when there is close contact, this novel coronavirus can transmit from person-to-person," said Dr Keiji Fukuda, WHO's assistant director-general for health security and environment, in Riyadh on Sunday.
And that should focus minds in the microbiological community.
According to WHO figures, between November 2002 and July 2003, the then-novel coronavirus Sars - Severe Acute Respiratory Syndrome - travelled to 29 countries, infecting 8,096 people and killing 774.
That was a fatality rate of 9.5 per cent. So far the new virus has infected only 38 people but it has killed 20 of them - a fatality rate of more than 52 per cent.
Locating the geographical source of a new virus is vital if the cycle of infection and onward transmission is to be broken, in much the same way as Sars was defeated in 2003, by stringent quarantine measures and travel restrictions to infected areas.
So far, 32 of the 38 known cases have either occurred in, or are probably related to, travel to Saudi Arabia. Of the six remaining cases, two are from Jordan, two from the UAE and one from Qatar, although it appears to be unknown whether any or all of these patients had recently travelled to Saudi Arabia.
No one knows where the Sars virus came from but it is thought to have jumped species from animals to humans. If so, then it is always possible that it could re-emerge.
Researchers in the Netherlands have sequenced the genome of the new virus and found it is closely related to HKU4 and HKU5, coronaviruses that infect the Tylonycteris and Pipistrellus bat species, although WHO says this evidence "is largely circumstantial and will remain so until the virus is demonstrated in an animal species".
If bats are the source - and hopefully the Saudi authorities are capturing animals in the region near the outbreak and checking their blood for virus or antibodies - does that mean bats could have bitten and infected the human victims?
Maybe, but WHO says experience with Sars in China and the Nipah virus in Malaysia - which in eight months in 1998 and 1999 infected 265 people, killing 105 of them - has shown that "intermediate hosts may sometimes play an important role in transmission to humans and that direct exposure to reservoir species is not needed for infection".
So the most likely scenario - and one proposed by Dr Ali Mohamed Zaki, who identified the first case in Saudi Arabia last September - is that the virus has been passed to humans from bats but via an intermediary species of domesticated animal, which in the Arabian peninsula probably means sheep, goats or even camels.
There is some circumstantial evidence for this. German researchers at the Klinikum Schwabing in Munich - where a 73-year-old man from Abu Dhabi was reported to have died in March after having been flown by air ambulance from hospital in the UAE - have despatched a member of their team to the emirate to collect samples from a camel herd with which the patient had been in close contact.
These investigations, carried out with the cooperation of Abu Dhabi's health authority, "are still continuing", Clemens Wendtner, professor of medicine at the University of Cologne, said.
Meanwhile, the international health community has yet to agree on a name for the new virus - a decision fraught with political considerations.
So far, organisations such as WHO and the UK's Health Protection Agency are sticking with nCoV - standing for novel, or new, coronavirus - while the US Centres for Disease Control and Prevention has declined even to abbreviate the virus to these initials.
The laboratory in Utrecht, Netherlands, that confirmed the Jeddah case labelled the virus after itself in a paper about the discovery published in November last year, with the "EMC" in HCoV-EMC/2012 standing for the Erasmus Medical Centre.
This has caught on in some quarters - at least 23 papers have been published subsequently using this name. But the International Committee on Taxonomy of Viruses is proposing MERS-CoV, with "MERS" standing for Middle East Respiratory Syndrome.
As the magazine Science reports, "Naming pathogens is a tricky issue". Historically, many diseases or their agents were named after where they were first found "but increasingly, scientists and public health officials have shied away from that system to avoid stigmatising a particular country or city".
That may be why Middle East Respiratory Syndrome, despite being an apparently accurate name, may struggle to catch on.
WHO officials, according to Science, coined Severe Acute Respiratory Syndrome for the then-novel 2003 coronavirus precisely "to prevent the disease being named 'Chinese flu' or something similar".