title: Detection by the polymerase chain reaction of Anaplasma phagocytophilum in tissues of persistently infected sheep.
abstract: To investigate the reservoir tissues of the tick-borne bacterium Anaplasma phagocytophilum in persistently infected sheep, six 6-month-old lambs were infected with a field isolate of the bacterium and maintained under tick-free conditions. At one and two weeks post-infection, A. phagocytophilum was detected in the peripheral blood of all lambs by examining May-Grünwald Giemsa-stained blood smears for classical intra-neutrophil inclusions, and by an A. phagocytophilum-specific nested PCR. After euthanasia at 3 months post-inoculation, peripheral blood and numerous tissue samples were collected from each lamb. DNA extracted from these samples was then subjected to PCR. All blood samples were PCR-negative but three lambs had PCR-positive tissues including intestinal wall and lymph nodes, thymus, bone marrow, kidney and bladder wall. The widespread nature of PCR-positive tissues suggested that circulatory cells may form the reservoir cells for A. phagocytophilum infection in carrier sheep, rather than lymphoid tissues as in rodents. PCR-positive tissue and blood samples were strikingly fewer in the experimentally infected sheep than reported earlier in tick-exposed carrier sheep under field conditions. It seems possible that tick infestation amplifies A. phagocytophilum infections in carrier sheep to a degree that enables tick transmission to occur.
authors.affiliation: Department of Production Animal Clinical Sciences, Norwegian School of Veterinary Science, Sandnes, Norway.
authors.forename: S
authors.initials: S
authors.lastname: Stuen
authors.forename: A N J
authors.initials: AN
authors.lastname: Casey
authors.forename: Z
authors.initials: Z
authors.lastname: Woldehiwet
authors.forename: N P
authors.initials: NP
authors.lastname: French
authors.forename: N H
authors.initials: NH
authors.lastname: Ogden
mesh_terms: D041081:Anaplasma phagocytophilum / Q000235:genetics / Q000302:isolation & purification*; D000818:Animals; D004195:Disease Models, Animal; D004197:Disease Reservoirs; D016873:Ehrlichiosis / Q000175:diagnosis* / Q000382:microbiology / Q000662:veterinary*; D025202:Molecular Diagnostic Techniques; D016133:Polymerase Chain Reaction / Q000379:methods*; D012756:Sheep; D012757:Sheep Diseases / Q000175:diagnosis / Q000382:microbiology*