A comparative study of clinical manifestations, haematological and serological responses after experimental infection with Anaplasma phagocytophilum in two Norwegian sheep breeds

摘要

Background: It has been questioned if the old native Norwegian sheep breed, Old Norse Sheep (also calledudNorwegian Feral Sheep), normally distributed on coastal areas where ticks are abundant, is more protected againstudtick-borne infections than other Norwegian breeds due to a continuously high selection pressure on pasture. Theudaim of the present study was to test this hypothesis in an experimental infection study.udMethods: Five-months-old lambs of two Norwegian sheep breeds, Norwegian White (NW) sheep and Old Norseud(ON) sheep, were experimentally infected with a 16S rRNA genetic variant of Anaplasma phagocytophilum (similarudto GenBank accession number M73220). The experiment was repeated for two subsequent years, 2008 and 2009,udwith the use of 16 lambs of each breed annually. Ten lambs of each breed were inoculated intravenously eachudyear with 0.4 ml A. phagocytophilum-infected blood containing approximately 0.5 × 106 infected neutrophils/ml. Six lambs of each breed were used as uninfected controls. Half of the primary inoculated lambs in each breed wereudre-challenged with the same infectious dose at nine (2008) and twelve (2009) weeks after the first challenge. Theudclinical, haematological and serological responses to A. phagocytophilum infection were compared in the twoudsheep breeds.udResults: The present study indicates a difference in fever response and infection rate between breeds ofudNorwegian sheep after experimental infection with A. phagocytophilum.udConclusion: Although clinical response seems to be less in ON-lambs compared to NW-lambs, further studiesudincluding more animals are needed to evaluate if the ON-breed is more protected against tick-borne infectionsudthan other Norwegian breeds.