Image copyright AFP Image caption The new virus emerged in 2012

The new Mers virus, which has killed half of those infected, is "unlikely" to reach the same scale as Sars, ministers in Saudi Arabia say.

Most of the 90 Mers cases reported so far have been in Saudi Arabia.

Mers is from the same group of viruses as the common cold and Sars, which killed 774 people.

However, a detailed analysis of the Saudi cases, published in Lancet Infectious Diseases, did warn of "major gaps" in understanding of the virus.

The Middle East respiratory-syndrome coronavirus (Mers) emerged in 2012 and has infected 90 people worldwide, 45 of them have died.

The global concern is that cases could spread much further, echoing the Sars outbreak.

So far there is little to indicate that Mers will follow a similar path to Sars Prof Ziad Memish, Deputy Minister for Public Health

Cases have been centred on the Middle East - with patients in Jordan, Qatar, Saudi Arabia and the United Arab Emirates. Additional cases in France, Germany, Italy, Tunisia and the UK have all been linked to travel to the Middle East.

Researchers in Saudi Arabia have published details of the 47 cases reported in the country.

They suggest a pattern of mostly older men being infected. Most cases were also in people with other medical problems, more than two-thirds of the reported cases also had diabetes.

Low threat

The lead researcher and Deputy Minister for Public Health, Prof Ziad Memish, said: "Despite sharing some clinical similarities with Sars, there are also some important differences.

"In contrast to Sars, which was much more infectious especially in healthcare settings and affected the healthier and the younger age group, Mers appears to be more deadly, with 60% of patients with co-existing chronic illnesses dying, compared with the 1% toll of Sars.

"Although this high mortality rate with Mers is probably spurious due to the fact that we are only picking up severe cases and missing a significant number of milder or asymptomatic cases.

"So far there is little to indicate that Mers will follow a similar path to Sars."

A report earlier this month showed that the virus struggled to spread in people.

However, it and the latest Saudi investigation both highlighted the need to find where the virus was coming from.

Prof Memish's report said: "Reducing the rate of introduction of Mers coronavirus into human beings is unpredictable because the source of the virus is not yet known.

"We are searching vigorously for the source."