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.
Curbing the spread of MERS?
Educating pilgrims to Mecca about the disease seems to be the only current viable option.
About two million people from more than 180 countries will visit Saudi Arabia in the next few months for Hajj – arguably the world’s largest mass gathering. In the absence of any travel restrictions imposed by the WHO, the Saudi authorities are faced with the challenge of ensuring that their guests return home healthy.
In response to the recent increase in MERS cases and the approaching Umrah and Hajj seasons, the WHO held an emergency meeting on 14 May and concluded that the MERS situation is serious, but not yet a Public Health Emergency of International Concern (PHEIC). The assessment was based on the lack of a direct evidence for sustained human-to-human transmissibility.
So, we are now left with the question of what should we do to curb the current MERS outbreak?
A commercial vaccine or antiviral therapeutic drug is not foreseeable in the near future. This is mainly because of the massive cost of a lengthy research and development endeavor and the complicated process of getting those products approved by the regulatory authorities.
Therefore, controlling MERS will require backing by big pharmaceutical companies, who will only invest these funds if they expect economic viability for such expensive products. Of course, studies will also be impeded by the current lack of a suitable animal model for MERS.
Twelve years down the line from the initial SARS outbreak, we still don’t have commercial human vaccines.
It might make more sense to develop vaccines for camels because animal vaccines usually cost less and require a shorter development/approval cycle. However, we still don’t know if camels are the only animal reservoirs.
Educating pilgrims to Mecca about the disease seems to be the only current viable option. Exercising caution, good personal hygiene and wearing masks are all constructive measures. Effective communication of the risks associated especially for those with pre-existing medical conditions, who usually suffer the worst complications of MERS, will definitely help reduce fatalities.
The WHO did not recommend airport screening of returning pilgrims after the Hajj trip as prior experience with the SARS and influenza H1N1 pandemics proved this procedure to be ineffective in reducing disease spread.
The incubation period of MERS can last 15 days. Infected people, who show no symptoms while incubating the virus, can pass unnoticed through thermal detectors. Distributing leaflets to passengers that describe MERS symptoms and actions to take if MERS is suspected seem a wiser option.
Breaking the transmission cycle is crucial for extinguishing the MERS outbreak. The WHO has recommended enforcing strict infection control measures at hospitals.
Transmission from camels is likely to continue, and until the mode of infection becomes clear, the WHO has urged people to stay away from camels and avoid their milk and other food products. Camels are of cultural and economic importance for Saudis; therefore culling them is not a realistic option and may not be effective at all. Increasing public health awareness and laboratory testing capacity will enhance our early MERS detection capabilities.
There is no doubt that we desperately need to conduct more surveillance and analyse more viral genomes in order to stay one step ahead of any changes that would render MERS-CoV more adapted to humans.
Although our armory in the battle against MERS is limited, we can still win some land through continuous vigilance, global collaborative efforts and transparent and swift sharing of information.
Islam Hussein is a researcher and virologist at MIT, Massachusetts. He is currently involved in several projects focused on identifying, tracking and investigating any genetic changes that might lead to the generation of potentially pandemic influenza strains.
Zaki AM. et al. Isolation of a novel coronavirus from a man with pneumonia in Saudi Arabia. The New England Journal of Medicine367: 1814-1820 (2012).
Memish ZA. et al. Middle East respiratory syndrome coronavirus in bats, Saudi Arabia. Emerging Infectious Diseases19: 1819-1823 (2013).
Briese T. et al. Middle East Respiratory Syndrome Coronavirus Quasispecies That Include Homologues of Human Isolates Revealed through Whole-Genome Analysis and Virus Cultured from Dromedary Camels in Saudi Arabia. mBio5: 1-5 (2014).