Bresium: The Jungle Amazons

From publisher blurb:

To the west and south of the Confederacy lies the tropical land of Bresium, governed by a gynarchy. The people who tamed Bresium were normal men and women bringing their families to find hope and peace in a new land. Disaster, however, befell the settlers in the form of a wasting disease unique to the jungles of Bresium. After an exposure of several weeks, all the males died off. Not willing to return to their lands of origin, the women remained to establish a new nation, one ruled by women.