A South Korean Air Force master sergeant stationed on the U.S.-built Osan Air Base has been diagnosed with the deadly MERS virus.

MERS, or Middle East respiratory syndrome, has hit the Asian nation hard, with over 40 cases diagnosed and four deaths prompting the closure of nearly 1,200 Korean schools, Forbes reports.

The sergeant has been quarantined and has shown no symptoms of the disease since testing positive for it. Meanwhile, about 100 of the sergeant's co-workers have been quarantined in their homes and barracks, Military Times reports. U.S. personnel on the base have not been quarantined, although they have been warned to take steps to avoid infection.

Air Force Col. Krystal Murphy, commanding the 51st Medical Group, told Military Times, "The virus spreads through close personal contact, such as caring for a MERS patient or sharing utensils and drink containers. We recommend everyone exercise caution and use good hygiene practices to prevent any further spread of MERS."

However, doctors are unsure of the exact transmission route of MERS, Forbes notes. Over 1,565 people who attended a medical symposium in South Korea with a doctor later found to have MERS have been asked to voluntarily quarantine themselves, and Seoul Police Chief Kang Shin-myun indicated that quarantines could become mandatory, CNN reported.

"We will deal strongly with anyone who escalates unnecessary sense of public uneasiness," he said in a press release.

All told, six civilians and 164 military personnel, all Korean, remain in quarantine on the Osan Air Base, CNN said.

MERS is believed to have originated with Saudi Arabian camels and, so far, 40 percent of more than 1,200 people diagnosed with the disease worldwide have died, Forbes reports. To date, more people have contracted MERS in South Korea than in any nation outside Saudi Arabia.

Forbes reported that there are fears that "the disease might spread among both Korean and U.S. forces at the base, regional headquarters of the U.S. Seventh Air Force," and officials of the Korean Centers for Disease Control and Prevention told the Korean news agency Yonhap that a number of soldiers are suspected of having contracted the disease.

So far, 30 of the Korean cases are linked to a single hospital, Military Times reports.

Dr. Jody Lanard, a specialist in disease outbreaks, told Military Times that the disease has been known to spread to people in hospital rooms unconnected to infected patients.

"For MERS, the contact doesn't always have to be close or direct. It can even mean visiting down the hall from a MERS patient's hospital room or coming into contact with a health worker who has treated a MERS patient and not washed their hands.

"That's why it is so important to cast a very wide net when tracing and quarantining MERS contacts," the Military Times said.

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