Table 3: Infectious agent determinants proposed to limit free-ranging bighorn sheep populations.

Agent categoryInfectious agentGeographic distribution of determinantLocations where determinant reportedDie-off attributed to determinant1Selected references

ParasitePsoroptes spp.Range-wideArizonaYes[143]
CaliforniaYes[28]
ColoradoYes[27, 157]
MontanaYes[130]
NevadaYes[130]
New MexicoYes[139, 158161]
OregonYes[109, 140]
TexasYes[110]
WashingtonYes[140]
WyomingYes[118, 130, 131, 141, 162]
Lungworm (Protostrongylus)Range-wide in mesic habitatsAlberta, CanadaYes[163]
CaliforniaNo[164]
ColoradoNo[27]
ColoradoYes[146, 165]
MontanaYes[113, 166]
MontanaNo[148, 167]
NevadaNo[168]
OregonNo[149]
UtahNo[169]
WyomingUnclear2[118, 122, 170]
Lungworm (Muellerius capillaris)LocalizedMontanaNo[128]
South DakotaNo[171]

BacteriaPasteurellaceaeRange-wideAlbertaYes[151]
ArizonaNo[172]
CaliforniaNo[164]
ColoradoNo[27]
ColoradoYes[19]
Hells Canyon (Washington, Idaho)Yes[18, 152, 173]
IdahoNo[174]
MontanaYes[17]
MontanaNo[128]
NevadaNo (endemic)[175]
OregonYes[176, 177]
WyomingYes[43]
Arcanobacterium (Corynebacterium)Presumed range-wideColoradoYes[157]
pyogenesMontanaYes[113, 166]
MycoplasmaUncertainArizonaYes[178]
Hells CanyonYes[18, 179]
Chlamydophila (Chlamydia) Psittaci UncertainWyomingYes[180]

VirusPI33, RSV4Presumed range-wideBritish Columbia, CanadaNo[181]
PI3, BRSV4Presumed range-wideHell’s CanyonYes[18]
PI33, BRSV4, BVD5, IBR6Presumed range-wideMontanaYes (some populations)[17]
PI33, RSV4, BVD5, IBR6, OPP7, BT8, EHD9Presumed range-wideCaliforniaNo[164, 182, 183]
PI33, BVD5, BT8, parvo virusPresumed range-wideColorado and WyomingNo[184]
RSV4Presumed range-wideArizona, California, Idaho, Montana, Nevada, New Mexico, Oregon, Utah, WashingtonNo[185]
ColoradoNo[186]
BRSV4, BT8, EHD9, CE10Presumed range-wideArizonaNo (EHD and BT isolated from 2 mortalities)[60, 187]
BT8Presumed range-wideTrans-Pecos, TexasNo[188]
CE10Presumed range-wideAlberta, British Columbia, CanadaNo (high morbidity, but low mortality)[189, 190]

1Mortality considered to be in excess of baseline levels;
2Mortality in excess of baseline versus endemic disease status was not clear;
3PI3: parainfluenza-3 virus;
4BRSV and RSV: bovine respiratory syncytial virus;
5BVD: bovine viral diarrhea virus;
6IBR: infectious bovine rhinotracheitis virus;
7OPP: ovine progressive pneumonia virus;
8BT: bluetongue virus;
9EHD: epizootic hemorrhagic disease virus;
10CE: contagious ecthyma virus.