Evaluation of Anaplasma phagocytophilum infection in experimentally inoculated sheep and determination of Anaplasma spp seroprevalence in 8 free-ranging sheep flocks in California and Oregon.
OBJECTIVE
To evaluate disease progression in sheep experimentally inoculated with Anaplasma phagocytophilum and determine the Anaplasma spp seroprevalence in sheep in free-ranging flocks in the Sierra Nevada foothills and Oregon Coast Range.


METHODS
10 mature ewes seronegative for Anaplasma spp and 251 sheep from 8 flocks.


METHODS
10 ewes received 1 of 3 treatments: A phagocytophilum Webster strain (n = 4), A phagocytophilum MRK strain (4), or human promyelocytic leukemia cells (control treatment [2]). Sheep were monitored for signs of clinical disease, and blood samples were obtained for serologic and PCR assay evaluation intermittently for 48 days. From a subsample of sheep from each of 8 free-ranging flocks, blood samples were obtained to determine Anaplasma spp seroprevalence.


RESULTS
Sheep inoculated with A phagocytophilum developed subclinical or mild disease, whereas sheep inoculated with the control treatment did not develop any signs of disease. Only 2 ewes seroconverted; both had received the MRK strain. Anaplasma-specific DNA was detected in blood samples from 1 sheep in the Webster strain-inoculated group and 3 sheep in the MRK strain-inoculated group. Sheep seropositive for Anaplasma spp were detected in 5 of 8 flocks, and flocks in the Sierra Nevada foothills had higher within-flock seroprevalence (22%) than did flocks in the Oregon Coast Range (6.4%).


CONCLUSIONS
Infection with A phagocytophilum in mature sheep generally resulted in subclinical disease. Higher Anaplasma spp seroprevalence in sheep in the Sierra Nevada foothills corresponded to the geographic distribution of anaplasmosis reported for dogs, horses, and humans.
Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California-Davis, Davis, CA 95616, USA.
Jennifer K
JK
Gorman
Bruce R
BR
Hoar
Nathan C
NC
Nieto
Janet E
JE
Foley
D041081:Anaplasma phagocytophilum / Q000235:genetics / Q000302:isolation & purification*; D000818:Animals; D000907:Antibodies, Bacterial / Q000097:blood; D002140:California / Q000453:epidemiology; D016009:Chi-Square Distribution; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D016873:Ehrlichiosis / Q000453:epidemiology / Q000382:microbiology / Q000662:veterinary*; D005260:Female; D008297:Male; D009922:Oregon / Q000453:epidemiology; D016133:Polymerase Chain Reaction / Q000662:veterinary; D011897:Random Allocation; D016036:Seroepidemiologic Studies; D012756:Sheep; D012757:Sheep Diseases / Q000453:epidemiology / Q000382:microbiology*
D000907:Antibodies, Bacterial; D004269:DNA, Bacterial