* Two cases so far, in Saudi and Qatari who went to Saudi
* Scientists developing rapid tests for use around the world
* Virus shares symptoms with SARS, may have animal origin (Adds pix, quotes from WHO spokesman, link to interview)
By Kate Kelland
LONDON, Sept 28 (Reuters) - A new and potentially fatal virus from the same family as SARS which was discovered in a patient in London last week appears not to spread easily from person to person, the World Health Organisation (WHO) said on Friday.
In an update on the virus, which has so far killed a Saudi man and made a patient from Qatar critically ill, the United Nations health agency said it was working with international partners to understand the public health risk better.
"From the information available thus far, it appears that the novel coronavirus cannot be easily transmitted from person to person," it said in a statement.
The WHO put out a global alert on Sunday saying a new virus had infected a 49-year-old Qatari who had recently travelled to Saudi Arabia, where another man with the same virus had died.
The Qatari was described as critically ill on Tuesday and is being treated in a London hospital. No new confirmed cases of infection with the virus have since been reported, the WHO said.
The new virus shares some of the symptoms of SARS, or Severe Acute Respiratory Syndrome, another coronavirus, which emerged in China in 2002 and killed around a tenth of the 8,000 people it infected worldwide.
Both patients who have so far been confirmed with the new virus suffered kidney failure.
"Given the severity of the two laboratory confirmed cases, WHO is continuing to monitor the situation in order to provide the appropriate response, expertise and support to its member states," the WHO statement said.
Scientists at the European Centre for Disease Prevention and Control (ECDC), which monitors disease in the European Union, said initial virology results and the separation in time of the only two confirmed cases suggest the infection may have developed from animals. Such diseases are known as zoonoses.
"(It) is quite probably of zoonotic origin and different in behaviour from SARS," the scientists wrote in a "rapid communication" study in the online journal Eurosurveillance.
Asked about transmission and the possibility of animal to human spread, WHO spokesman Glenn Thomas said investigations were continuing.
"But from the evidence we have, and given that there are only two cases confirmed so far and there was a distance and time distance between the two cases, (the) assumption is that it isn't easily transferable person to person," he told reporters.
The WHO's clinical guidance to its 194 member states says health workers should be alert to anyone with acute respiratory syndrome and requiring hospitalisation who had been in the Middle East where the virus was found or in contact with a suspected or confirmed case within the previous 10 days.
The U.N. agency has not recommended any travel restrictions in connection with the new virus, but said it was working closely with Saudi authorities on health measures for Muslims making the haj pilgrimage to Mecca.
Health experts said rapid progress has already been made in figuring out the nature and genetic makeup of the new coronavirus, and in coming up with tests.
"We are developing with our partners sensitive and specific diagnostic assays and these should be available in the next few days," Thomas told a briefing at WHO headquarters in Geneva.
"If any national authority is concerned about a patient who is under investigation, if they want to contact us, we can put them in touch with these laboratories and provide initial tests for any cases which are suspicious," he added. (Additional reporting by Stephanie Nebehay in Geneva; Editing by David Stamp and Giles Elgood)