* Patient is second MERS case imported to United States
* Health authorities checking other UK-based passengers
* Deadly virus first emerged in Middle East in 2012 (Adds details, quotes, CDC statement, background on virus)
By Kate Kelland
LONDON, May 12 (Reuters) - British health authorities said on Monday they had found a second case of the deadly Middle East Respiratory Syndrome (MERS) virus in a person transiting through London, who flew from Jeddah in Saudi Arabia to the United States on May 1.
The passenger, who is the second known MERS infected patient to have flown to the United States, was on Saudi Airlines Flight 113 from Jeddah to London, and transferred at Heathrow for onward travel, Public Health England (PHE) said in statement.
The MERS virus first emerged in September 2012 and has since infected almost 500 people in Saudi Arabia. There have also been sporadic cases across the Middle East, as well as in Europe, Asia, and now the United States.
The U.S. Centers for Disease Control and Prevention (CDC) confirmed the presence of MERS with health officials from Florida.
The CDC said in a statement it was the second "imported" instance of MERS, meaning a traveller contracted the virus in another country and brought it to U.S. shores. The first such imported case involved a man who flew from Saudi Arabia and travelled to Indiana earlier this month.
Nick Phin, head of respiratory diseases for PHE, said any UK-based passengers who had been on that flight who become unwell with a fever, cough or shortness of breath within 14 days of being in the Middle East "should make sure they call their doctor and tell them where they have travelled".
"Risk of transmission is considered extremely low but, as a precautionary measure, PHE is working with the airline to be able to contact UK passengers who were sitting in the vicinity of the affected passenger to provide health information," the PHE said.
Saudi Arabia is still the focal point of the outbreak, and health officials there are dealing with an upsurge in the number of detected cases over the past month.
MERS, which causes coughing, fever and sometimes fatal pneumonia, is a coronavirus from the same family as SARS, or Severe Acute Respiratory Syndrome, which killed around 800 people worldwide after first appearing in China in 2002.
There is no vaccine for MERS, and around a third of the 483 known to have been infected with it in Saudi Arabia have died.
Scientists have linked the human cases of the virus to camels, and Saudi authorities warned on Sunday that anyone working with camels or handling camel products should take extra precautions by wearing masks and gloves. (Reporting by Kate Kelland; Editing by Robin Pomeroy)