Research Article: Prevalence of Anaplasma phagocytophilum infection and effect on lamb growth

Date Published: May 13, 2011

Publisher: BioMed Central

Author(s): Lise Grøva, Ingrid Olesen, Håvard Steinshamn, Snorre Stuen.


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.

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.

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. 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.

Partial Text

Tick-borne fever (TBF) is one of the main challenges in Norwegian sheep farming during the grazing season [1]. TBF is caused by the bacteria Anaplasma phagocytophilum, transmitted by the tick Ixodes ricinus, and may cause direct (lamb deaths) and indirect loss (reduced growth) in sheep farming. The normal distribution area of I. ricinus ticks in Norway is the coastal areas of Norway as far north as Brønnøysund in Nordland county (N 65°30′), Norway [2-4]. A. phagocytophilum infected lambs are commonly found in areas with ticks [2,5]. Climate change (i.e. warmer winter climate), changes in land use (i.e. bush encroachment) and an increase in the deer population are factors expected to increase the populations of ticks. An extension of the northern margin of the population distribution of I.ricinus and to higher altitudes has been observed [6,7], and has given rise to concerns that challenges with TBF will increase in Norway in the coming years.

In summary, the present study supports previous findings that A. phagocytophilum infection is widespread. It also shows that an A. phagocytophilum infection affects live weight. However, A. phagocytophilum infections do not always cause substantial direct or indirect losses.

The authors declare that they have no competing interests.

All authors contributed in designing the study and supervising the writing of the manuscript. LG was responsible for data collection, the statistical analysis and writing the draft manuscript. IO contributed particularly with input on statistical analysis. SS contributed particularly with input into the discussion of the results. All authors approved the final manuscript.




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