The Rifleman (1958) : 1x15

Ward Haskins guns down Joe Flecker, who has evidence that could be used to blackmail him. Haskins thinks the information was given to Lucas, since he brought Flecker to the doctor before he died. Stirred up by Haskins behavior, Lucas goes through Flecker's things, finding a wanted poster for Haskins in the sole of Flecker's boot. He also finds Doc Burrage drinking. Doc is discouraged because three children have died of an anthrax epidemic that he has the new serum for, but nobody is willing to allow him to administer it in time. Haskins rides out to the ranch and is bitten by Flecker's horse, which is now believed to have anthrax. Mark overhears about how anthrax always causes death and is worried because he had bitten by Flecker's horse, also.