Jack Leach is leaving England's tour of South Africa after battling a series of health issues, including a recent bout of sepsis.

Leach has not been available for selection since arriving on tour and will return home before the last two Tests of the series to complete his recovery.

The left-arm spinner was hospitalised during the previous series in New Zealand and the England and Wales Cricket Board have revealed for the first time that he was suffering from sepsis, an immune response known as 'blood poisoning' that can be life-threatening in its most extreme forms.

Leach, who also suffers from Crohn's Disease, was cleared to make the trip to South Africa but then found himself hit by bouts of flu and gastroenteritis which swept the camp last month.

The England and Wales Cricket Board said in a statement that the 28-year-old "has struggled to fully recover from sepsis he picked up during the tour of New Zealand" and "has not been able to reach the expected levels of fitness to be considered for selection".

Head coach Chris Silverwood wished the player well and hopes to have him back in the fold for a spin-friendly series in Sri Lanka in March.

"It has been an unfortunate time for Jack with illness and since the Test series in New Zealand six weeks ago, he hasn't been able to get 100 per cent fit," he said.

"He is a great lad to have around the squad and his infectious personality and popularity will be missed.

"However, his focus has to be getting himself better and receiving the optimum levels of recovery and treatment, which is best served back in England without any distractions.

"I have no doubt that he will return to full fitness in the medium-term and hopefully he will recover in time for our tour of Sri Lanka in March."

Leach's Somerset team-mate Dom Bess played in the second Test win at Cape Town having originally arrived as cover and is in line to retain his place at Port Elizabeth on Thursday.

Leach is the third player to depart a tour that has been disrupted by frequent medical bulletins, joining Rory Burns (ankle) and James Anderson (rib).

A total of 11 squad members and six backroom staff fell ill before or during the first Test in Centurion.