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Quote from: DOUBLELUNG on January 15, 2009, 07:39:26 PMThe epizootic pneumonia outbreaks in bighorn sheep are caused by Pasteurella haemolytica, which evolved with Old World sheep, and which is endemic in them (both wild and domestic species) and causes no major disease issues for them. New World sheep lack exposure and immunity to P. haemolytica, and once exposed can remain dormant in individuals until they are stressed; then the disease breaks out, is highly infectious, and will kill 50-90+% of a bighorn herd. So far, no bighorns have developed immunity, though after 140 years of exposure some are more resistant than others (that just means the outbreaks and die-offs are less frequent). Outbreaks kill all sex and age classes.A second cause is lungworm, also an Old World sheep disease, which also causes pneumonia. In herds with lungworm, lambs will be born and adults aren't usually affected - but all or most lambs will die before winter. Herds eventually blink out as the adults die and aren't replaced. So far, the only effective measure is spatial separation. Even then, when subadult rams wander and disperse, they often come into contact domestic sheep or goats, and then present the danger they will bringthe infection to a bighorn herd. Thus, most of not all wild sheep states' wildlife agencies have policies that bighorns that contact domestic sheep should be killed ASAP (or, in the case of WA, killed if they cannot be captured and quarantined). There's no state law against having domestic sheep in an occupied bighorn range, unfortunately. Forest Service and BLM both have policies that are supposed to prevent commingling, but then politics creep into the mix.
