Plague Ship by Andre Norton, Science Fiction, Space Opera, Adventure

Told from the viewpoint of Dane Thorson, an apprentice-Cargo Master, a "lanky, very young man in an ill-fitting Trader's tunic," Plague Ship takes the crew of the Solar Queen to Sargol, where the enigmatic feline natives seem very reluctant to trade away their fabulous scented gemstones. When Dane Thorson discovers an herb that the Salariki are willing to swap for their gems, he brings the ship into a peril he could never have imagined -- a strange plague that comes from venomous stowaways from Sargol. . . .