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  • Author or Editor: Bruce Hoar x
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Objective—To determine whether sequelae of infection differed among single versus double infection with Anaplasma phagocytophilum or Anaplasma marginale, with and without tick salivary extract, in cattle.

Animals—Eighteen 13-month old steers.

Procedures—Treatment groups of 3 cattle each included A marginale inoculated ID followed on day 35 by A phagocytophilum without tick saliva, A phagocytophilum followed on day 10 by A marginale without tick saliva, A marginale followed on day 35 by A phagocytophilum with tick saliva, A phagocytophilum followed on day 10 by A marginale with tick saliva, tissue culture control injection, and tick saliva control injection. Infection was monitored via clinical observations, CBC, serologic testing, and PCR analysis of blood and tissues.

Results—Infected cattle had significantly reduced weight gain. Anemia occurred 25 to 32 days after A marginale infection, which was attenuated by tick saliva. Parasitism was greater if cattle had not previously been inoculated with A phagocytophilum. Nine of the 12 treated cattle had positive results of PCR analysis for A phagocytophilum from at least 1 blood sample. Five tissue samples had positive results of PCR analysis for A phagocytophilum; PCR results for A marginale were positive in spleen, lung, lymph node, heart, and ear skin of infected cattle.

Conclusions and Clinical Relevance—Results indicated an important biological interaction between A marginale and A phagocytophilum infection as well as with tick saliva in disease kinetics and severity in cattle, which may be important for interpretation of diagnostic tests and management of disease in areas where both pathogens occur.

Full access
in American Journal of Veterinary Research


Objective—To evaluate seasonal patterns and risk factors for Escherichia coli O157:H7 in feces in a beef cattle herd and determine strain diversity and transition in E coli over time by use of multiple-locus variable-number tandem-repeat analysis (MLVA) and pulsed-field gel electrophoresis (PFGE).

Sample Population—456 samples of freshly passed feces collected over a 1-year period from cattle in a range-based cow-calf operation located in the foothills of the Sierra Nevada Mountains in California.

Procedures— E coli O157:H7 was recovered from feces by use of immunomagnetic separation and 2 selective media. Virulence factors were detected via reverse transcriptase-PCR assay. Escherichia coli O157:H7 isolates were subtyped with MLVA and PFGE. Prevalence estimates were calculated and significant risk factors determined. A dendrogram was constructed on the basis of results of MLVA typing.

Results—Overall prevalence estimate for E coli O157:H7 was 10.5%, with the prevalence lowest during the winter. Mean temperature during the 30 days before collection of samples was significantly associated with prevalence of E coli O157:H7 in feces. Nineteen MLVA and 12 PFGE types were identified.

Conclusions and Clinical Relevance—A seasonal pattern was detected for prevalence of E coli O157:H7 in feces collected from beef cattle in California. Subtyping via MLVA and PFGE revealed a diversity of E coli O157:H7 strains in a cow-calf operation and noteworthy turnover of predominant types. Given the importance of accurately determining sources of contamination in investigations of disease outbreaks in humans, MLVA combined with PFGE should be powerful tools for epidemiologists. (Am J Vet Res 2010;71:1339–1347)

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in American Journal of Veterinary Research


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.

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

Procedures—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 and Clinical Relevance—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.

Full access
in American Journal of Veterinary Research