NACHES, Wash. (AP) — State and federal biologists plan to euthanize wild bighorn sheep in the Naches area to curb the spread of a deadly pneumonia outbreak.

Richard Harris of the Washington Department of Fish and Wildlife says biologists will spend the next several weeks removing sheep from the Tieton herd, about 10 miles west of Naches.

The herd is currently estimated at between 35 to 50 animals. Harris says almost all of the animals will likely need to be euthanized, because most of them are believed to be infected with the disease that causes pneumonia.

The disease is often fatal in wild bighorns and can affect the survival rate of lambs later born to animals that survive the disease.

There is no treatment or preventative vaccine.