Experimental infection of dairy calves with Ehrlichia chaffeensis.
Human monocytic ehrlichiosis (HME) is a zoonotic emerging tick-borne disease with clinical signs that range from mild symptoms to multiple organ failure and death. Ehrlichia chaffeensis, the aetiologic agent of HME, is reported to infect a divergent range of mammals. Although cattle are common hosts of the primary vector of this pathogen, the susceptibility of this host to E. chaffeensis has not been reported to date. This study was undertaken to determine if cattle could provide a useful infection model of E. chaffeensis. Dairy calves were injected with DH82 cells infected with the Arkansas, St Vincent or 91HE17 strain of E. chaffeensis, and monitored for signs of clinical ehrlichiosis and for infection of peripheral blood and ticks by PCR assay. Splenectomized and spleen-intact calves were injected with cryopreserved stabilates of E. chaffeensis-infected DH82 cells for the first experiment. Mild clinical signs were occasionally observed among these calves, and only two blood samples were PCR-positive, while several ticks fed on each calf tested PCR-positive. The second experiment involved injection of normal calves with active cultures of the same E. chaffeensis strains. Interestingly, three of six calves inoculated with active cultures became recumbent and died or had to be euthanized. All of the surviving calves in this experiment tested PCR-positive on multiple dates, but fewer ticks fed on these calves were PCR-positive. These results suggest that a bovine disease model could facilitate the understanding of factors that affect the severity of HME.
Delos Santos
Jose R C
JRC
Department of Veterinary Preventive Medicine, Ohio State University, Columbus, OH, USA.
Boughan
Kirsten
K
Department of Veterinary Preventive Medicine, Ohio State University, Columbus, OH, USA.
Bremer
William G
WG
Department of Veterinary Preventive Medicine, Ohio State University, Columbus, OH, USA.
Rizzo
Brian
B
Department of Veterinary Preventive Medicine, Ohio State University, Columbus, OH, USA.
Schaefer
John J
JJ
Department of Entomology, Ohio State University, Columbus, OH, USA.
Rikihisa
Yasuko
Y
Department of Veterinary Biosciences, Ohio State University, Columbus, OH, USA.
Needham
Glen R
GR
Department of Entomology, Ohio State University, Columbus, OH, USA.
Capitini
L A
LA
University Laboratory Animal Resources, Ohio State University, Columbus, OH, USA.
Anderson
David E
DE
Department of Veterinary Clinical Sciences, Ohio State University, Columbus, OH, USA.
Oglesbee
Michael
M
Department of Veterinary Biosciences, Ohio State University, Columbus, OH, USA.
Ewing
S A
SA
Department of Veterinary Pathobiology, Oklahoma State University, Stillwater, OK, USA.
Stich
Roger W
RW
Department of Veterinary Pathobiology, University of Missouri, Columbia, MO, USA.
D000818:Animals; D002417:Cattle; D004198:Disease Susceptibility / Q000662:veterinary*; D018469:Ehrlichia chaffeensis / Q000472:pathogenicity*; D016873:Ehrlichiosis / Q000382:microbiology / Q000473:pathology / Q000662:veterinary*; D006801:Humans; D023421:Models, Animal; D016133:Polymerase Chain Reaction / Q000662:veterinary