READER S DIGEST OVERVIEW: RESPIRATORY DISEASE IN BIGHORN SHEEP Peregrine Wolff, DVM Nevada Department of Wildlife
During the Lewis & Clark expedition (1804 1806) There may have been 2 million bighorn sheep on the North American landscape HISTORY
Reports of epizootics in bighorn sheep occurred after the advent of domestic livestock grazing in bighorn sheep range suggesting introduction of a novel pathogen in the 1800 s
When bighorn sheep co mingle with domestic sheep it often results in an all age die off from pneumonia lamb recruitment in subsequent years is poor
Recent die offs Winter 2009 10 9 die offs 5 western states Montana Nevada Utah Washington Wyoming +/ 900 mortalities Epizootics continue to be a barrier to recovery of the species
Complicating Factors Often there was no single pathogenic species or biovarient isolated from all or even most of the lungs Bighorn sheep domestic sheep encounters do not always result in a die off Bighorn sheep can experience death with no known prior contact with domestic sheep Pathogenic bacteria species are cultured from healthy BHS
What the Science tells us
The Primary Players Family Pasteurellaceae Pasteurella or Bibersteinia trehalosi Pasteurella multocida Mannheimia haemolytica We forget that these bacteria lead dynamic lives in a We forget that these bacteria lead dynamic lives in a rapidly changing world
Why are these organisms so deadly? It s the leukotoxins Soluble toxins enhance pathogenicity Affinity for leukocytes ++ in ruminants Lead to death of the cells/tissue damage Compared to Domestic Sheep BHS neutrophils are more sensitive to effects of leukotoxins BHS have a decreased dantibody response BHS antibodies don t protect as well against leukotoxins
What do we know about M. hemolytica and B. trehalosi? Varying levels of leukotoxin activity M. hemolytica +Lkt (+) Death in 48 hrs.
vs. B. trehalosi cultured most frequently M. haemolytica cultured most frequently Most M. haemolytica & Most B. trehalosi & M. B. trehalosi haemolytica = = low leukotoxin activity it high h leukotoxin activity it
B. Trehalosi and P. multocida are more frequently isolated from lungs of BHS that had died from pneumonia than M. haemolytica B. trehalosi Grows faster, higher density in vitro >6 hours in culture M. haemolytica cannot be identified with conventional culture methods Field sampling may allow B. trehalosi to continue to overgrow in vivo I th 2010 di ff l ti PCR iti f In the 2010 die off, lung tissue was PCR positive for M. haemolytica even though it was culture negative
Genotyping studies of M. haemolytica are identifying phylogenetic relationships Pasteurella spp. may exchange genetic material (including coding for virulence factors) In order to increase our understanding of epidemiology of the bacteria we are no longer able to rely on phenotypic strain classification cat of Pasteurella e a spp.
10 meters for 30 days Transmission of Mannheimia hemolytica from domestic sheep to bighorn sheep: Unequivocal Demonstration with Green Fluorescent Protein Tagged Organisms. Lawrence P.K, et al.
Fence line contact for 60 days 3 of 4 BHS had tagged bacteria within 30 days
Comingled and all BHS died or were euthanized in 4 9 days 1 BHS began coughing 7 days before comingling 1 animal died 2 days after comingling
The Other Player Mycoplasma ovipneumoniae Mycoplasma arginini i i M. ovipneumoniae causes cilliary dysfunction Allowing invasion of secondary pathogens N t i f M i i b Numerous strains of M. ovipneumoniae can be recovered from the same outbreak
M. ovipneumoniae Respiratory dz consistent with M. ovipneumoniae M. ovipneumoniae + death from pneumonia M. haemolytica
Mycoplasma ovipneumoniae Serological evaluation of healthy BHS herds (no evidence of pneumonia) yielded no seropositive animals 60% of apparently healthy animals asfrom herds edsthat had experienced die offs were seropositive M. ovipneumoniae may allow less virulent serotypes of M. haemolytica to cause fatal pneumonia in BHS
OTHER PLAYERS? Disease Agents: Respiratory viruses PI3, IBR, BRSV, BVD Pasteurella sps. from cattle Internal Parasites Environmental factors: Trace mineral deficiencies Animal densities Habitat Loss/ Degradation
Listen to what the sheep have been trying to tell us Bighorn sheep and domestic sheep don t play well together How can we intelligently mange for both species on and ever shrinking landscape
Our goal as wildlife vets is to understand and, where feasible, control specific risk factors that may cause or precipitate disease in humans, domestic species or wildlife, and to provide information concerning such factors and risks to our agency animal managers