Prevalence of Anaplasma phagocytophilum infection and effect on lamb growth

Summary

Background: A major challenge in sheep farming during the grazing season along the coast of south-western
Norway is tick-borne fever (TBF) caused by the bacteria Anaplasma phagocytophilum that is transmitted by the tick
Ixodes ricinus.
Methods: A study was carried out in 2007 and 2008 to examine the prevalence of A. phagocytophilum infection
and effect on weaning weight in lambs. The study included 1208 lambs from farms in Sunndal Ram Circle in Møre
and Romsdal County in Mid-Norway, where ticks are frequently observed. All lambs were blood sampled and
serum was analyzed by an indirect fluorescent antibody assay (IFA) to determine an antibody status (positive or
negative) to A. phagocytophilum infection. Weight and weight gain and possible effect of infection were analyzed
using ANOVA and the MIXED procedure in SAS.
Results: The overall prevalence of infection with A. phagocytophilum was 55%. A lower weaning weight of 3%
(1.34 kg, p < 0.01) was estimated in lambs seropositive to an A. phagocytophilum infection compared to
seronegative lambs at an average age of 137 days.
Conclusions: The results show that A. phagocytophilum infection has an effect on lamb weight gain. The study
also support previous findings that A. phagocytophilum infection is widespread in areas where ticks are prevalent,
even in flocks treated prophylactic with acaricides.