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READER’S DIGEST OVERVIEW:RESPIRATORY DISEASE INRESPIRATORY DISEASE IN
BIGHORN SHEEP
Peregrine Wolff, DVMN d D f WildlifNevada Department of Wildlife
HISTORYDuring the Lewis & Clark expedition(1804 – 1806)There may have been 2 million bighorn sheep on the North Americanlandscape
Reports of epizootics in bighorn sheep occurred after the advent of domestic livestock grazing in bighorn sheep range –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 fromsheep it often results in an all age die‐off from pneumonia lamb recruitment in subsequent years is poorlamb recruitment in subsequent years is poor
Recent die‐offs
Winter 2009‐10
9 di ff9 die‐offs 5 western states
MontanaNevadaUtahWashingtonWyoming
+/‐ 900 mortalities/ 900 mortalities
Epizootics continue to be a barrier to recovery of the species
Complicating FactorsOften 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 PlayersFamily Pasteurellaceae
Pasteurella or Bibersteinia
Pasteurellalt idBibersteinia
trehalosimultocida
Mannheimiahaemolyticay
We forget that these bacteria lead dynamic lives in aWe 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
It s the leukotoxins
•Affinity for leukocytes ‐ ++ in ruminants•Lead to death of the cells/tissue damage
Compared to Domestic Sheep•BHS neutrophils are more sensitive to effects ofleukotoxins
h d d b d•BHS have a decreased antibody response •BHS antibodies don’t protect as well against leukotoxins
What do we know about M hemolytica and B trehalosi?M. hemolytica and B. trehalosi?
Varying levels of leukotoxin activityVarying levels of leukotoxin activity
M. hemolytica +Lkt (+) Death in 48 hrs.
B trehalosi cultured most M haemolytica cultured
vs.
B. trehalosi cultured most frequently
M. haemolytica cultured most frequently
Most M. haemolytica & Most B. trehalosi & M. B. trehalosi
=l l k t i ti it
haemolytica=
hi h l k t i ti itlow leukotoxin activity high leukotoxin activity
B. Trehalosi and P. multocida are more frequently isolated from lungs of BHS thatfrequently isolated from lungs of BHS that had died from pneumonia than M. haemolyticaM. haemolytica
B. trehalosi ‐ Grows faster, higher density in vitro
>6 hours in culture –M. haemolytica cannot be identified with conventional culture methodswith conventional culture methods
Field sampling may allow B. trehalosi tocontinue to overgrow in vivo
I th 2010 di ff l ti PCR iti fIn 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)g )
In order to increase our understanding of epidemiology of the bacteria we are noepidemiology of the bacteria we are no
longer able to rely on phenotypic strain classification of Pasteurella spp. st a c ass cat o o asteu e a spp
10 meters for 30 days
Transmission of Mannheimia hemolytica from domestic sheep to bighorn sheep: Unequivocal Demonstration with Green Fluorescentbighorn 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 1 BHS began died or were euthanized
in 4‐9 days
gcoughing 7 days before comingling
1 animal died 2 days after cominglingcomingling
The Other PlayerMycoplasma ovipneumoniaeM l i i iMycoplasma arginini
M. ovipneumoniaecauses cilliary dysfunction Allowing invasion of secondary pathogens
N t i fM i i bNumerous strains of M. ovipneumoniae can be recovered from the same outbreak
M. ovipneumoniae Respiratory dz consistent withM ovipneumoniaewith M. ovipneumoniae
M. ovipneumoniae + death from pneumoniap pM. haemolytica
Mycoplasma ovipneumoniaey p p
Serological evaluation of healthy BHS herds (no evidence of pneumonia) yielded no seropositive animals
60% of apparently healthy animals from herds that had 60% o appa e t y ea t y a a s o e ds t at adexperienced die‐offs were seropositive
M. ovipneumoniaemay allow less virulent serotypes of M. haemolytica to cause fatal pneumonia in BHS
OTHER PLAYERS?Disease Agents:
Respiratory viruses – PI3, IBR, BRSV, BVDPasteurella sps. from cattleInternal Parasites
Environmental factors:Environmental factors:Trace mineral deficienciesAnimal densitiesAnimal densitiesHabitat 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