by Peter Openshaw, PhD

Coronaviruses cause about 15% of common colds, which are normally mild. So why are public health authorities so alarmed about the latest coronavirus disease, Middle East Respiratory Syndrome (MERS)?

With the first reports of person to person transmission, MERS-CoV is uncomfortably reminiscent of the Severe Acute Respiratory Syndrome (SARS)-CoV, which emerged in South East Asia 12 years ago. SARS-CoV had an alarming ability to transmit in healthcare facilities, in hotels and in residential blocks. In one case, at least 70 hospital staff were infected by a single case; in another, a patient in Hanoi infected 63 staff members, of whom 3 died.  These super-spreading events were terrifying, but the introduction of stringent hygiene ultimately led to the elimination of SARS. The final tally was 8096 cases and 774 deaths (9.6% mortality).

MERS-CoV bears remarkable phylogenetic similarity to a bat coronaviruses (as did SARS), but may be transmitted by contact with camels (rather than civet cats). Infections were first reported in Saudi Arabia in 2012. Similar to SARS, MERS causes not only pneumonia but also sometimes severe systemic complications including renal failure and gastrointestinal disease. Moreover, MERS cases tend to progress to respiratory failure more rapidly dis SARS cases. This may be related to the older age group that it tends to affect and to the presence of (comorbid) illnesses.

MERS-CoV has so far has shown little ability to spread from person to person, but there has been a sharp increase in the reported number of MERS cases in recent months. As of May 28, 2014, the WHO reports 636 confirmed cases and 193 deaths (30% mortality). Of these cases, 306 have been reported in the past two months, mostly from Saudi Arabia. Cases are now appearing of primary or secondary infections in several countries, including Iran and the USA.

This is an outbreak that needs to be watched carefully, especially in relation to the upcoming Hajj. We lack effective antiviral drugs or vaccines, and poorly understand the pathogenesis of severe disease. The best that can be done at present is to study transmission, and to institute infection control measures in the hope that MERS can be beaten in the same way as SARS.