Health authorities in Qatar announced the second confirmed case in a week of the MERS coronavirus, with a 29-year-old man infected and in intensive care.
The Qatari patient suffers from asthma and has been in contact with another patient infected with MERS.
He is "in a critical condition and is under intensive care," the Supreme Health Council said in a statement late Monday.
On 20 August, the authorities announced the first infection in the Gulf state of a 59-year-old Qatari.
Another Qatari national with the infection died in a London hospital on 28 June.
The virus has killed 47 people worldwide since September, 41 of them in Saudi Arabia which neighbours Qatar.
MERS is considered a cousin of the SARS virus that erupted in Asia in 2003 and infected 8,273 people, nine per cent of whom died.
Like SARS, it is thought to have jumped from animals to humans, and shares the former's flu-like symptoms -- but differs by causing kidney failure.
Researchers have pointed to the Arabian camel, or dromedary, as a possible host of the virus.
Scientists studying the new virus have found older patients, men, and people with underlying medical conditions at particular risk.