The severity of the SARS epidemic, which infected more than 8,000 people over a decade ago, killing around 10% of them, has heightened fears over the emergence of its deadly close cousin: Middle East Respiratory Syndrome (MERS), a zoonotic viral disease caused by a novel coronavirus (nCoV).
The virus has infected hundreds of humans, claiming the lives of around 30% of patients, and the total global count of MERS-CoV cases has recently surged alarmingly. April 2014 saw the number of new infections doubling, and they are still mounting.
Human travel carried MERS-CoV from Saudi Arabia – the virus’s place of origin and its epicenter – across oceans to several other countries, and with no vaccines or antivirals, reminiscent of the SARS tragedy, there is a growing fear of a new viral pandemic.
Mode of transmission mystery
Initial sampling of the virus suggested that MERS-CoV, like SARS, originated in bats, but a closer examination revealed that MERS-CoV was identical to a whole-genome sequence of a virus found in dromedary camels in Saudi Arabia.
However, there are many questions about its spread, including how the virus is transmitted from camels to humans. We still don’t know whether camels are the only animal reservoirs of this virus. Further research in coming weeks should bring more answers.
Approximately 75% of MERS-CoV cases didn’t have a history of camel contact, which strongly suggests a human-to-human transmission pathway for this virus. The sudden hike in the number of new infections throughout April also begs an explanation. Is the virus mutating to gain more adaptation to humans? It’s a scary possibility.
But analyzing the sequences of a limited number of whole genomes from the new cases of MERS in Saudi Arabia in April, Christian Drosten, a virologist at the University of Bonn in Germany, found no evidence of mutations particularly in the receptor-binding domain of the spike protein that binds to receptors on human cells – known as dipeptidyl peptidase 4 (DPP4).
This would be good news if only we had sequenced a larger fraction of the circulating virus pool. In addition, RNA viruses do mutate frequently and may undergo further adaptation changes in the future.
The Saudi Arabia connection
So far, all MERS cases have been related somehow to the Middle East, with a majority of cases being reported in Saudi Arabia. As it stands, more than 60% of the recent MERS cases began as clusters of hospital-acquired infections among healthcare workers in King Fahd hospital in Jeddah.
Generally speaking, immediately upon suspecting MERS, patients should be placed in negatively pressured isolation rooms, where the air potentially carrying the virus is forced through special filters before it gets circulated out through a ceiling vent system. But this didn’t happen with Saudi Arabia’s first cases.
The WHO visited Jeddah in early May to conduct on-site investigations and concluded that the Jeddah surge could have been the result of a seasonal increase in primary cases, associated with an increase in camel births or pollination of bat roosts-bearing palm trees. This would have sparked the hospital outbreaks that were then exacerbated by suboptimal infection control measures.
In an interview with the local Saudi online newspaper, Al-Watan, Abdullah Al-Asiri, director of infection control at the Saudi Ministry of Health, revealed that two MERS patients stayed in the ER of the hospital for about six days before MERS was confirmed and patients quarantined.