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

Abstract

BackgroundIt has been questioned if the old native Norwegian sheep breed, Old Norse Sheep (also called Norwegian Feral Sheep), normally distributed on coastal areas where ticks are abundant, is more protected against tick-borne infections than other Norwegian breeds due to a continuously high selection pressure on pasture. The aim of the present study was to test this hypothesis in an experimental infection study.MethodsFive-months-old lambs of two Norwegian sheep breeds, Norwegian White (NW) sheep and Old Norse (ON) sheep, were experimentally infected with a 16S rRNA genetic variant of Anaplasma phagocytophilum (similar to GenBank accession number M73220). The experiment was repeated for two subsequent years, 2008 and 2009, with the use of 16 lambs of each breed annually. Ten lambs of each breed were inoculated intravenously each year 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 were re-challenged with the same infectious dose at nine (2008) and twelve (2009) weeks after the first challenge. The clinical, haematological and serological responses to A. phagocytophilum infection were compared in the two sheep breeds.ResultsThe present study indicates a difference in fever response and infection rate between breeds of Norwegian sheep after experimental infection with A. phagocytophilum.ConclusionAlthough clinical response seems to be less in ON-lambs compared to NW-lambs, further studies including more animals are needed to evaluate if the ON-breed is more protected against tick-borne infections than other Norwegian breeds.

Bovine anaplasmosis in Turkey: First laboratory confirmed clinical cases caused by Anaplasma phagocytophilum

“…However, morulae were not observed in the two clinical cases that were RLB positive for A. phagocytophilum. This finding is supported by a previous report of Anaplasma DNA detected as early as five days before inclusions were observed by blood smear microscopy (Stuen et al, 2011). We found parasitemia of 0.2-1.6% in animals, consistent with the view that the percent of infected leukocytes varies markedly .…”

“…We found parasitemia of 0.2-1.6% in animals, consistent with the view that the percent of infected leukocytes varies markedly . In addition, a recent study found the infection rate to be significantly different on days 3, 6, 7, and 8 in experimentally infected sheep (Stuen et al, 2011). Therefore, molecular diagnostic tools represent a more sensitive method, and the time frame for detection of A. phagocytophilum is longer when using molecular methods than with thin blood smears Nieder et al, 2012).…”

“…In each blood smear, 20 fields (minimum of 5000 red blood cells) were screened for the presence of A. marginale and A. centrale in the erythrocytes. A minimum of 500 neutrophils were also screened in each smear, and the number of cells containing Anaplasma basophilic morulae was recorded and the parasitemia was calculated as the percent of infected neutrophils (Stuen et al, 2011). Counts were made without knowledge of the molecular results.…”

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

“…Investigators of another study 26 in which a large sample of inoculum of A phagocytophilum was subdivided into small aliquots for the in-oculation of individual sheep (a procedure similar to that used in the study reported here) found that a few aliquots lacked a sufficient infective dose because of minor stochastic differences. All sheep in the present study received approximately the same dose of A phagocytophilum, but only a small proportion seroconverted or developed bacteremia.…”

A comparison of nonlinear mixed models and response to selection of tick-infestation on lambs

“…Individual variation in response to A . phagocytophilum infection in sheep is evident and shown by Granquist et al [27] and Stuen et al [28]. Furthermore, genetic variation in lamb survival on tick exposed pastures has also been reported [29].…”