Via New Scientist: Threatwatch: Is the MERS virus spreading its wings? Excerpt:
The virus is turning up in many of the people being tested because they are contacts of known cases, but many of these people do not themselves develop the severe pneumonia that has killed 93 of the 243 known cases of MERS. That means it is probably infecting a lot more people than we know about.
That may be of little importance from an epidemiological perspective if people with mild or asymptomatic infections cannot spread the disease any further. There's no evidence that they can – but many MERS cases had no contact with known cases before they fell ill, suggesting there may be such silent spread.
Much will be resolved when epidemiologists work out whether the virus really does come from camels. Many – though not all – cases not clearly linked to other sick humans had contact with camels before falling ill. Recent research suggests camels may be the normal home of the virus, rather than merely passing it on from another animal.
The case of the Filipino healthcare worker is just one of the large proportion of MERS cases among healthcare professionals. In Jeddah, 38 cases have been diagnosed in a clustered outbreak that began in late March, many of them healthcare workers. Four doctors at the King Fahad Hospital have tendered their resignations in protest, and authorities are offering danger pay to medical staff who treat people with MERS.
This is uneasily reminiscent of the virus's Chinese cousin, SARS, which spread worldwide in 2003, and struck healthcare workers in particular. This threat is amplified in the Arabian peninsula, where many healthcare workers are foreign guest-workers – who, like the Filipino nurse, return to their home countries carrying the virus with them. This week, Saudi health authorities stated that 36 of the country's first 194 cases were foreigners.
The Malaysian case raises another risk. The 54-year-old man had just performed umrah, the minor Muslim pilgrimage to Mecca outside the holy month of Ramadan: he flew from Jeddah, the site of the current outbreak, and died 13 April in Johor state, near Singapore.
Malaysian authorities are trying to trace other passengers on Turkish Airlines TK93 from Jeddah to Istanbul and TK60, from Istanbul to Kuala Lumpur on March 29. Some of the 64 people reportedly quarantined in the man's home town are said to have symptoms.
Occasional sick travellers – also confirmed in the UK, France, Germany, Italy and Tunisia – have not so far spawned secondary outbreaks. What is worrying about the Malaysian case is that he was a pilgrim. From the beginning, public health officials have worried that most MERS has been in Saudi Arabia, which welcomes 3 million pilgrims annually for the hajj, and comparable numbers for umrah during the rest of the year.
The Saudis have been very careful: for the last hajj they recommended that elderly or unwell would-be pilgrims stay home instead, and announced afterwards that no cases of MERS were found in any pilgrims.
Now, that is no longer true – and in fact it may not have been true before, either, as many pilgrims return to countries considerably less medically advanced than Malaysia. Pilgrims who return with the virus might fall ill or spread it silently without being tested. As with many things about MERS, whether that is happening remains a mystery for now – an increasingly worrying one.