What is it?

  • MERS, short for Middle East Respiratory Syndrome, is a newcomer on the international health scene: It was first discovered in a patient from Saudi Arabia in 2012. It is caused by a bat virus that appears to infect many dromedary camels in the Arabian peninsula and occasionally jumps to humans.
  • MERS caused jitters among public health experts because it is related to SARS, which emerged in Asia in 2003 and quickly caused a worldwide outbreak, along with major panic, before it was stopped in its tracks. (Both MERS and SARS are caused by coronaviruses, a group that also includes some common cold viruses.) Many worried that MERS might develop into a pandemic, as SARS almost did. So far, that hasn’t happened, but scientists are watching closely.

A camel in Qatar, one of the countries that has had MERS cases. Credit: Martin Enserink

What are the symptoms?

Symptoms can range from mild to very severe and include fever, cough, shortness of breath, and pneumonia. Some patients also have diarrhea and other gastrointestinal symptoms. Of the almost 1900 patients reported by early 2017, more than 35% had died. (The real fatality rate is likely lower because some patients with mild symptoms did not go to a doctor and weren’t diagnosed as MERS patients.) People who are older and those with weakened immune systems or other conditions are at higher risk of severe disease and death.

How does it spread?

  • Some people appear to contract MERS from contact with an infected camel. How this happens exactly isn’t clear. But we know that camels in the Middle East and Africa can carry the virus; many have antibodies against MERS, which means they were infected at some point.
  • The virus also spreads between people. This type of transmission occurs through very close contact with a patient, usually in hospitals where infection control isn’t perfect. Human-to-human transmission has led to ‘clusters’ of MERS cases. But the virus doesn’t spread very easily outside hospitals, which is one reason why MERS hasn’t caused a big epidemic so far.
  • The virus circulates primarily in the Arabian Peninsula; around 80% of cases have been in Saudi Arabia. Patients traveling from this region have ‘imported’ the virus to some 20 countries elsewhere, where it has started new outbreaks. The biggest one was in 2015 in South Korea, where 186 people got sick, most of them in hospitals, and 36 died.

MERS cases in Saudi Arabia, Korea, and other countries between 2012 and 2016. Credit: WHO

How is it treated?

Doctors have tried a number of candidate drugs to treat MERS, but so far none have proven beneficial; treatment consists of ‘supportive care’ to fight symptoms and help the patient’s body defeat the virus.

How can it be prevented?

  • There are no MERS vaccines yet for either camels or humans.
  • Because we don’t know exactly how the virus jumps from camels to humans, it’s also not clear how best to prevent this type of transmission. WHO guidelines include regular handwashing before and after touching camels, staying away from sick animals, and avoiding the consumption of raw or undercooked camel milk and meat.
  • To prevent human-to-human transmission, family members should avoid contact with patients, and hospitals should apply strict infection control measures, including the use of protective masks, gowns, and gloves, and proper ventilation. People who haven been in contact with a MERS patient can be quarantined until it’s clear they are not infected themselves.
  • One problem is that it’s often not initially clear that a patient has MERS, because the symptoms overlap with those of many other diseases. During the time it takes to establish a MERS diagnosis, a patient can unwittingly infect new people.

What’s the outlook?

  • The fact that MERS is not easily transmissible between people has somewhat eased the worries that it will trigger a pandemic. But nobody can rule out mutations to the virus that would allow it to spread faster and more easily. And MERS is still a health risk for people who come into contact with camels and the people around them.
  • The easiest way to prevent humans from getting sick might be to develop a MERS vaccine for camels. Several such vaccines are in development. The question is whether such a vaccine would get widely adopted; camel breeders, farmers, and owners have little incentive to buy it because camels don’t seem to get very sick from MERS, if at all.
  • MERS’s original habitat is bats, as it is for SARS. Both diseases are reminders that other viruses are lurking in bats, awaiting their chance to jump the species barriers and sicken humans.


A WHO fact sheet about MERS.

A report about the development of camel vaccines, based on a meeting in Saudi Arabia.

The MERS outbreak in Korea.