SEOUL, June 6 -- No mutation in the Middle East Respiratory Syndrome (MERS) virus was found in South Korea suffering from the virus which has infected 50 people as of Saturday since the first patient was reported on May 20.

Lee Ju-shil, head of the Korea National Institute of Health, told a press briefing Saturday that little difference was identified in gene sequencing between MERS virus in South Korea and the Middle East.

The state-run research center under the Korea Centers for Disease Control and Prevention (CDC) separated a virus from sputum of the second South Korean patient to compare it with the Middle East virus in sequence listing

The sample was sent to the U.S. Centers for Disease control and Prevention, a South Korean virus institute and a research institute in the Netherlands to jointly analyze the virus.

The sample almost matched up in gene sequencing with the Middle East virus by more than 99 percent, bringing a conclusion that the South Korean virus is not a mutant, Lee said.

The unusually fast spread of the MERS in South Korea fueled expectations for the mutated virus, but it turned out to be untrue.

Nine new cases of the MERS contagion were reported on Saturday in South Korea. Four infectees died of the viral disease until now. South Korea became the most MERS-contagious outside the Middle East.

The MERS is a respiratory illness caused by a new type of corona-virus, similar to the SARS virus that killed more than 770 people worldwide following a 2003 outbreak. There is no known vaccine or treatment for the MERS, of which fatality rate reaches 40.7 percent.

The first MERS case was spotted in Saudi Arabia in 2012. The World Health Organization has reported more than 1,000 cases of MERS globally and more than 400 deaths.