Episode 80 of "Andromeda"
s04e14 The Others

The crew rescues two people from a spaceship, the leaders of opposing sides in a long civil war on a nearby planet. The two warring sides have built an immense wall separating the northern and southern halves of the planet, and the Northerners are suffering from a plague that is blamed on the Southerners. After Dylan contracts the plague, the crew try to assist in settling the dispute and find a cure for the plague, but nothing goes as planned.