SPOKANE — A lawsuit that seeks to prevent disease outbreaks in bighorn sheep herds living in the Okanogan-Wenatchee National Forest has been filed in federal court in Eastern Washington.

The lawsuit contends the Forest Service is placing bighorn sheep at high risk of disease outbreaks by authorizing domestic sheep grazing in the forest near bighorn herds.

Monday’s lawsuit was brought by WildEarth Guardians and Western Watersheds Project. It said officials for the Okanogan-Wenatchee National Forest have known about the high risk that domestic sheep grazing poses to bighorn sheep for at least a decade.

Domestic sheep carry a pathogen that causes pneumonia in bighorns and reduces lamb survival rates for years. Once disease is in a bighorn herd, it can cause low lamb survival for a decade, and members of that herd can easily transmit the disease to nearby bighorn herds. There is no cure or vaccine.

In October, the Washington Department of Fish and Wildlife killed 12 bighorns from the Quilomene herd after a domestic ewe commingled with the herd. Less than two weeks later, WDFW found the disease within the Cleman Mountain herd.

Bighorn sheep were wiped out during the era of Western settlement. The animals have slowly recovered to about 5% of their historic population levels.