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
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
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
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
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
Although MERS cases have been detected in Europe, all patients were
residents or had connections to Jordan, Qatar, Saudi Arabia, or the United Arab
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'.