U.K. Prime Minister Boris Johnson has tested positive for COVID-19 and will self-isolate for seven days.

Johnson declared the diagnosis on Twitter on Friday morning, with symptoms of a cough and a temperature on Thursday afternoon.

Suffering mild symptoms, the prime minister is the first leader of a major Western country made public to have contracted the novel coronavirus.

"I've developed mild symptoms of the coronavirus," he said in a video posted on Twitter.

Johnson is as of now the world's highest-profile political leader to reveal a contraction of the disease.

"I am now self-isolating, but I will continue to lead the government's response via video-conference as we fight this virus," he wrote on Twitter.

The news sparked concerns for his pregnant partner Carrie Symonds.

According to U.K. health officials, pregnant women should be in the high-risk group for the coronavirus pandemic and have been requested to remain at home.

He said he will continue to spearhead the government's response to the virus via video conference.

"But be in no doubt that I can continue, thanks to the wizardry of modern technology, to communicate with all my top team, to lead the national fight back against coronavirus," Johnson persisted.

He underwent testing for the coronavirus on Thursday on the recommendation of the U.K.'s chief medical officer after experiencing "mild symptoms," according to a statement by a spokesperson for No. 10 Downing Street.

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The increase of Spain coronavirus cases

The declaration on Friday came as Spain registered 769 new fatalities in the past 24 hours, bringing the tally of deaths in the country due to the coronavirus to 4,858.

According to Johns Hopkins University, the United States has now recorded more coronavirus cases than any other nation with more than 86,000 infections.

The spokesman said Johnson, 55, exhibited symptoms on Thursday one day after he participated in the prime minister's weekly question time in the chamber of the House of Commons.

Health Secretary Matt Hancock has also tested positive for the coronavirus. He also announced his infection on Friday via Twitter and tried to put to rest concerns that Westminster's response to the coronavirus might be compromised.

Johnson received his diagnosis at midnight which was hours after he appeared outside the door of No. 10 Downing Street, clapping in support of National Health Service workers, with the chancellor, Rishi Sunak, in tow.

Hancock, who has a role at NHS, said he would self-quarantine until next Thursday.

What happens if the Prime Minister falls very ill?

As of now, Johnson will remain in his post. In the event that the prime minister falls seriously infected, the U.K. Foreign Secretary Dominic Raab will act as his "designated survivor."

Raab, who tested negative for the coronavirus twice, would be slated as the de facto prime minister as Johnson received treatment.

The Queen had last engaged with Johnson on March 11 and "remains in good health," according to Buckingham Palace.

After resisting more rigid measures for more than a week, the prime minister imposed a lockdown on Britain to try to flatten the virus' spread.

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