Medical Matters: Sars-like virus Mers would have to adapt genetically to threaten us

Mon, Jul 7, 2014, 18:00

Apologies for the acronym-laden opening sentence, but could Mers become the next Sars?

Middle East respiratory syndrome (Mers), which causes coughing, fever and sometimes fatal pneumonia, is a coronavirus from the same family as severe acute respiratory syndrome (Sars), which killed about 800 people worldwide after first appearing in China in 2002.

The Mers virus, also known as MERS-CoV, first emerged in September 2012, and has since infected almost 700 people around the world.

Most cases have occurred in Saudi Arabia and other Middle Eastern countries while there have been sporadic cases in Europe and Asia. And US health officials recently confirmed the country’s second case of Mers; in a healthcare worker living in Saudi Arabia, who had travelled to Orlando, Florida, to visit relatives.

Major threat

Not for the first time, air travel has facilitated the spread of a new infectious disease. Sars was a good example of this, with Canada in particular affected by the arrival of the virus direct from China.

Mers also has a high death rate and limited human-to-human transmission, leading to fears that it could be a novel Sars in the making.

Experts say the Mers virus would have to adapt further genetically to pose a major threat to humans.

When Sars spread to humans from civets, which are cat-like animals, it underwent two genetic mutations that allowed it to target a receptor in humans, making it much more infectious and leading to rapid spread.

So far there is no evidence of this happening with the new virus.

However, there has been a recent acceleration in the number of Mers cases. More than half of cases reported to date emerged in April alone and the World Health Organisation says some 75 per cent of cases appear to be due to human-to- human infection.

The virus poses a particular threat to healthcare workers. Although the overall chance of contracting the virus is small, doctors around the world have been advised to have a high index of suspicion in people with breathing difficulties that are not explained by any other illness and who have recently travelled to the Middle East.

Risk of spread

A recent study in the Lancet Infectious Diseases modelled how the virus could spread during air travel, and found a small but real risk of spread from those infected during flight.

The risk ranged from one new infection in a five-hour flight in first class, to 15 infections from a “superspreader” – a highly contagious carrier – travelling for 13 hours in the economy class section of a plane.

And an article in Eurosurveillance noted how central the Middle East has become for global travel. Dubai, Abu Dhabi and Qatar have become huge hubs for their national airlines and now closely link Asian and Pacific countries with the rest of the world.

“The region has witnessed a dramatic increase of traffic growth in the last decade (153 per cent of relative increase in Saudi Arabia in the period from 2002 to 2011, 240 per cent in Jordan, 408 per cent in Qatar, 512 per cent in the United Arab Emirates, against a global relative increase of 168 per cent),” the authors write.

“Analysis of the air-traffic data suggests that other countries than the ones already affected are at high risk of MERS-CoV importation through infected passengers, in particular in the southern regions of Asia.”

Other Mers mysteries remain. While it seems likely that camels are the source of infection, you would expect that people interacting intensely with camels might represent a high proportion of cases, but that is not the case.

Nonetheless, Irish tourists looking forward to a break in the Middle East should probably avoid close contact with camels, with regular hand washing de rigueur before and after any trekking activity involving animals.

The answer to my opening question is that Mers could, in the future, resemble Sars. But we are probably at least two genetic mutations away from that, so fingers crossed.

mhouston@irishtimes.com muirishouston.com

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