LONDON — British Prime Minister Boris Johnson says he is as “fit as a butcher’s dog” after being instructed to self-isolate for 14 days because he recently came in contact with someone who has since contracted coronavirus.

In a video message posted Monday on Twitter from his London apartment at Downing Street, Johnson said it didn’t matter that he has already endured COVID-19 and is “bursting with antibodies.”

The quarantine requirement comes at the start of a crucial week for Johnson’s Conservative government that includes discussions over a post-Brexit trade deal with the European Union. Negotiators are meeting in Brussels this week with time on a deal fast running out.

Johnson, who contracted the virus in April and spent three days in intensive care as his symptoms worsened, met with a small group of lawmakers for about a half-hour on Thursday, including one, Lee Anderson, who subsequently developed symptoms and tested positive.

Health Secretary Matt Hancock said it was right that the prime minister goes into self-isolation even though he’s already had coronavirus as people “can catch it twice.”