Johnson becomes first world leader to say he has coronavirus

Johnson will self-isolate in Downing Street for seven days after a test on Thursday found he had the virus, his spokesman James Slack told reporters on Friday. Meals will be left at Johnson's door while he continues to work by video-conference, Slack said.

"I've developed mild symptoms of the coronavirus, that's to say a temperature and a persistent cough," Johnson said in a video posted on Twitter. "Be in no doubt I can continue, thanks to the wizardry of modern technology, to communicate with all my top team, to lead the national fightback against coronavirus."

The disclosure adds to the uncertainty over the British government's response to the coronavirus, which had already been criticized for being too slow. The pound erased its gains against the dollar after Johnson's announcement, while European stocks extended their losses.

"You could be the greatest technical analyst or economics professor on the planet but there are no text books that tell you how to trade Boris Johnson contracting the coronavirus," James Sullivan, chief executive officer of Divento Financials Ltd., said by phone.

Johnson was assessed by National Health Service staff on the advice of the chief medical officer Chris Whitty. The prime minister is the latest high profile individual to contract the virus after Prince Charles, the heir to the U.K. throne, also tested positive.

"I wish the prime minister a speedy recovery and hope his family are safe and healthy," Labour Leader Jeremy Corbyn said on Twitter.

The prime minister's condition means Chancellor of the Exchequer Rishi Sunak has had to move out of his office in No. 11 Downing Street, which is now being used by Johnson. While the premier works from No. 10, his official flat is above No. 11, next door. The doors connecting the two buildings have been closed off.

Foreign Secretary and First Secretary of State Dominic Raab would stand in for Johnson if the prime minister is unable to carry out his duties.

Johnson ended his Twitter video by thanking the public services for their efforts and reiterated his optimism that the country will overcome the virus challenge.

"The more effectively we all comply with those measures, the faster our country will come through this epidemic and the faster we'll bounce back," Johnson said. "We're going to beat it and we're going to beat it together. Stay at home, protect the NHS and save lives."