The Somerset duo of offspinner Dom Bess and medium-pacer Craig Overton have been called up to England's Test squad ahead of the first Test against South Africa - starting on Boxing Day in Centurion - after a bug swept through the touring party, leaving a number of players unwell. The two are expected to reach Johannesburg on Saturday morning.

As reported earlier, England's tour match against South Africa A, which starts on Friday, was downgraded from first-class status because of the ongoing effects of illness in the line-up.

Among those to have fallen ill were Jofra Archer, Stuart Broad and Jack Leach, none of whom travelled to the game. The ECB said in a statement that the match will be a "three-day friendly match with only 11 players batting or fielding at any point in time".

The call-ups highlight England's level of concern ahead of the first Test after such a disrupted build-up. Leach travelled to New Zealand last month as the Test team's first-choice spinner, but was left out in Hamilton and then hospitalised by a bout of gastroenteritis. Although legspinner Matt Parkinson is with the squad in South Africa, he has yet to play a Test and only appeared in four Championship games for Lancashire in 2019.

Bess made his Test debut at Lord's last year when Leach, his Somerset team-mate, suffered a broken finger. Although he has had to play the understudy role at Taunton, he provides more of an all-round option, having impressed with the bat during his two Tests against Pakistan.

The call for Bess also confirms England's cautious approach to plans for a Moeen Ali comeback. After being dropped during the summer, Moeen has taken an indefinite break from Test cricket and Ashley Giles, England director of men's cricket, said earlier this week that the allrounder "needs to make sure he's ready" before he is selected again.

Overton, meanwhile, featured as recently as the fourth Ashes Test at Old Trafford in September. He will provide England with another seam-bowling option, amid concerns over the fitness of Broad and Archer and the fact James Anderson is only just back from a calf injury that ruled him out of the majority of the Ashes.