Dar-Kosis (medical) an incurable, wasting disease akin to the Earth disease of leprosy; also known as the Sacred Affliction. So named because it is regarded as being holy by the Priest-Kings

Suddenly to my horror, I saw the quarry of the larl, It was a human being, moving with surprising alacrity over the rough ground. To my astonishment, I saw it wore the yellow cerements of the sufferer of Dar Kosisvirulent, incurable, wasting disease of Gor. 
Book 10, Tarnsman: pg 149

He was now bent and crooked, like a broken blasted shrub in his yellow shroud like robe. The hood concealed his face. ...Pointing to its shadowed concealed face it whispered "The Holy Disease." That was the literal translation of Dar Kosis - the Holy Disease or equivalent the Sacred Affliction. The disease is named that because it is regarded as being holy to the Priest-Kings, and those who suffer from it are regarded as consecrated to the Priest-Kings. Accordingly it is regarded as heresy to shed their blood. On the other hand, the Afflicted, as they are called, have little to fear from their fellow men. Their disease is so highly contagious, so invariably devastating in its effects, and so feared on the planet that even the boldest of outlaws gives them a wide berth. Accordingly, the afflicted enjoy a large amount of freedom of movement on Gor. They are of course, warned to stay away from the habitations of men, and if they approach too closely, they are sometimes stoned. Oddly enough, casuistically, stoning the Afflicted is not regarded as a violation of the Priest Kings supposed injunction against shedding their blood. As an act of charity, Initiates have arranged at various places Dar Kosiswhere the Afflicted may voluntarily imprison themselves to be fed with food hurled downward from the backs of passing tarns. Once in a Dar Kosis pit the Afflicted are not allowed to depart. I was glad that it was night and that the hood of the man was drawn, for I had no desire to look on what pieces of flesh might still cling to his skull. 
Book 10, Tarnsman: pg 150
"No." said Flaminius, smiling. "No," he took another swallow, "I thought to find," he said, "an immunization against Dar Kosis." 
"Dar Kosis is incurable," I said. 
"At one time," he said, "centuries ago men of my Caste claimed age was incurable. Others did not accept this and continued to work. The result was the Stabilization Serums." 
Dar Kosis or the Holy Disease or Sacred Affliction is a virulent wasting disease of Gor. Those afflicted with it commonly spoken of simply as the afflicted ones may not enter into normal society. They wander the country side in shroud-like yellow rags beating a wooden clapping device to warn men from their path; some of them volunteer to be placed in Dar Kosis pits several of which are in the vicinity of Ar, where they are fed and given drink, and are of course isolated; the disease is extremely contagious. those who contract the disease are regarded by law as dead. 
Book 5, Assassin: pg 265

"I had" he said, "shortly before the fire developed a strain of urts resistant to the Dar-Kosis organism; a serum cultured from their blood was injected in other animals, which subsequently we were unable to infect." 
Book 5, Assassin: pg 267

"Dar-Kosis," I said, "is regarded as an instrument of Priest Kings, used to smite those who displease them." 
"Another myth of Initiates" said Flaminius unpleasantly. 
"But how do you know that?" I queried. 
"I do not care," said Flaminius, "if it is true or not. I am a Physician." 
Book 5, Assassin: pg 266