Flocks from each county in Norway were included in this study, such that flocks in Ixodes areas along the coast and areas with a high number of winterfed sheep were preferred. However, representative flocks in each area were chosen and sampled by the local veterinarians.
Serum samples from sheep flocks were obtained in October/November. Samples from 10 sheep were randomly collected in each herd, around half of the samples were from lambs (6 to 7-months-old). A questionaire was filled out by the veterinarian during the visit of each flock, including questions about ectoparasitic treatment, Ixodes infested pastures, earlier treatment against TBF, and occurrence of tick-associated infections. Four sheep flocks were chosen from each of the 18 counties in Norway, except from the county of Sør-Trøndelag, where 8 flocks were selected. The reason for this was that the northernmost observation of tick-borne fever so far has been in the county of Sør-Trøndelag [27 ].
An indirect immunofluorescence antibody assay (IFA) was used to determine the antibody titre to Ehrlichia equi [1 (link)]. Two-fold dilutions of sera were added to slides precoated with E. equi antigen (Protatek International and Organon Teknika). Bound antibodies were visualized by fluorescein-isothiocyanate (FITC)-conjugated rabbit-anti-sheep immunoglobulin (Cappel, Organon Teknika). Sera were screened for antibodies at dilution 1:40. If positive, the serum was further diluted and retested. A titre of 1.6 (log10 reciprocal of 1:40) or more was regarded as positive.
The statistical analysis was done according to [14 ]. The overall seroprevalence and mean antibody titre were estimated and stratified by ectoparasitic treatment and age. Statistical calculations were done by using Statistix®, version 4.0 (Analytical software). Statistical analyses on seroprevalence were performed using a chi-square test and the antibody titres were compared using a Students t-test for independent samples. Significance was set at p < 0.05.
Serum samples from sheep flocks were obtained in October/November. Samples from 10 sheep were randomly collected in each herd, around half of the samples were from lambs (6 to 7-months-old). A questionaire was filled out by the veterinarian during the visit of each flock, including questions about ectoparasitic treatment, Ixodes infested pastures, earlier treatment against TBF, and occurrence of tick-associated infections. Four sheep flocks were chosen from each of the 18 counties in Norway, except from the county of Sør-Trøndelag, where 8 flocks were selected. The reason for this was that the northernmost observation of tick-borne fever so far has been in the county of Sør-Trøndelag [27 ].
An indirect immunofluorescence antibody assay (IFA) was used to determine the antibody titre to Ehrlichia equi [1 (link)]. Two-fold dilutions of sera were added to slides precoated with E. equi antigen (Protatek International and Organon Teknika). Bound antibodies were visualized by fluorescein-isothiocyanate (FITC)-conjugated rabbit-anti-sheep immunoglobulin (Cappel, Organon Teknika). Sera were screened for antibodies at dilution 1:40. If positive, the serum was further diluted and retested. A titre of 1.6 (log10 reciprocal of 1:40) or more was regarded as positive.
The statistical analysis was done according to [14 ]. The overall seroprevalence and mean antibody titre were estimated and stratified by ectoparasitic treatment and age. Statistical calculations were done by using Statistix®, version 4.0 (Analytical software). Statistical analyses on seroprevalence were performed using a chi-square test and the antibody titres were compared using a Students t-test for independent samples. Significance was set at p < 0.05.
