The world is watching South Korea as the latest outbreak of Middle East respiratory syndrome (MERS) unfolds. But how exactly the virus jumps to humans in the first place is still unknown, and clues to that puzzle lie thousands of kilometres away.
The cluster of hospital-associated cases in South Korea — the largest MERS outbreak outside the Middle East — has so far killed 7 people and infected 95, according to the World Health Organization (WHO). Hundreds of schools have been shut. Although the causal coronavirus, MERS-CoV, is considered a potential pandemic threat, specialists told Nature that they expect authorities to quickly bring this outbreak under control.
Since it was first detected in Saudi Arabia in 2012, MERS-CoV has infected around 1,200 people worldwide, roughly 450 of whom have died, according to the WHO. The virus is thought to originate in bats and to jump to humans through an intermediate animal, such as camels. It does not easily spread between people, partly because it infects deep areas of the lungs, and is not coughed out. Most of the human infections, however, were the result of human-to-human spread, which can occur in hospitals when certain medical procedures combine with poor infection control to disseminate the virus. The latest clusters began when a South Korean man returned to Seoul from the Middle East, and visited four health-care facilities before he was diagnosed.
There is always a chance that as the virus spreads, it could acquire mutations that allow it to spread more easily between humans. But on 6 June, the South Korean health ministry announced that it had sequenced the virus in the current outbreak and that it was almost identical to past sequences from the Middle East. On the same day, the Chinese Center for Disease Control and Prevention posted a separate sequence to the publicly available GenBank database, from a man infected in the South Korean outbreak who then travelled to China, where he felt ill. Christian Drosten, director of the Institute of Virology at the University of Bonn Medical Centre in Germany has analysed this sequence and says that it is shows only minor mutations compared with Middle Eastern strains, none in areas of the genome thought to influence infectiousness.