Middle East Respiratory Syndrome (MERS), a potentially lethal respiratory virus first identified last year in Saudi Arabia, may be transmitted by jumping repeatedly from animals to humans, DNA sequencing suggests. Human-to-human transmission appears more complex than was previously thought.
Published in The Lancet, the study sequenced the genomes of 21 viruses isolated from infected patients in Saudi Arabia. By comparing the genomes, scientists were able to partially reconstruct the evolution of the virus and unearth clues as to its transmission.
Paul Kellam, professor of viral pathogenesis at the UK's Sanger Institute and University College London and a lead author of the study, told Reuters: 'Our findings suggest that different lineages of the virus have originated from the virus jumping across to humans from an animal source a number of times'.
MERS was first identified in early 2012 after a 60-year-old man in Saudi Arabia contracted an unknown fatal respiratory disease. Since then, over 100 people have been infected globally, and at least 52 have died.
Clinically, MERS resembles severe acute respiratory syndrome (SARS); infected patients develop a cough and fever accompanied by pneumonia and kidney failure. The SARS outbreak in 2002 and 2003 was responsible for 8,000 infections worldwide, killing almost 10 percent of patients.
Both infections are caused by coronaviruses, enveloped RNA viruses that infect the gastrointestinal and respiratory tracts of mammals and birds. Currently, six coronoviruses, including MERS, are known to be infectious to humans. Most infections with coronaviruses are mild and will be experienced as a common cold by most people. However, in the case of SARS and now MERS, the infections can be of much greater severity.
The sequencing study indicates that MERS passed from animals to humans multiple times in different geographic locations, with a common ancestor host acting as the original animal source. There is concern that the animals acting as 'reservoirs' for the virus may carry the infection without showing signs of illness.
According to the World Health Organisation, the virus has not yet been isolated from any animal. In the case of SARS, civets - small mammals that sold in Chinese food markets - were the first identified reservoir.
The genetic analysis presented in the MERS paper suggests that the closest relative of the virus might be found in bats. Some infected patients describe a history of interaction with visibly ill camels and goats, and these animals may also be a source of transmission. Studies to identify the animal reservoirs are currently ongoing.
Although MERS cases have been detected in Europe, all patients were residents or had connections to Jordan, Qatar, Saudi Arabia, or the United Arab Emirates.
Professor Ali Zumla, from University College London, a senior co-author of the study, said that the current risk of global spread appeared 'minimal'.
'Two mass gatherings events attracting over 8 million pilgrims have occurred in Mecca, Saudi Arabia, since the discovery of the MERS virus 12 months ago […] and yet no MERS-CoV cases have been reported from these events to date', he said.
Nonetheless, Professor Zumla added, 'watchful surveillance and vigilance is required'.