Health agencies are racing to determine the origins of a Mers outbreak in Saudi Arabia, after three people with no direct contact to camels contracted the coronavirus.

The pathogen, known as Middle East respiratory syndrome, is a close relative of Sars-Cov-2 but has a far higher fatality rate – 35 per cent of confirmed cases have died, according to the World Health Organization (WHO).

The virus comes from dromedary camels, and most previous outbreaks have been traced back to people working in close contact with the mammals or their raw milk.

Yet authorities have not been able to link the current outbreak – which was detected when a 56-year-old school teacher in the capital Riyadh went to hospital in early April – to the animals, raising concerns that milder cases could be spreading undetected.