Abstract
Granulocytic Ehrlichia infection in sheep is common in Norway in areas with Ixodes ricinus. In this study, 2 sheep flocks that had been grazing on I. ricinus infested pastures the previous season, were blood sampled after being housed indoors for nearly 6 months during wintertime. Thirty animals from each flock were examined for granulocytic Ehrlichia infection in the peripheral blood by blood inoculation studies, stained blood smear evaluation, polymerase chain reaction (PCR) analysis and serology (IFAantibodies). The animals were sampled twice within a three-week period, the first time before and the second time after lambing. Two sheep in one flock were found Ehrlichia positive by both blood smear evaluation and PCR before lambing, and 3 sheep were found positive after lambing; 2 by blood smear examination and 3 by PCR. In the other flock, no sheep was found infected before lambing, but 2 ewes were found positive after lambing by both blood smear evaluation and PCR. In the first flock, 87% of the animals were found seropositive before lambing, and the mean antibody titre (log 10 ± SD) to E. equi was 2.45 ± 0.401. In the second flock, 40% were found seropositive before lambing, and the mean antibody titre was 1.93 ± 0.260. Seroprevalence and mean antibody titre in these 2 flocks were significantly different (p < 0.001). The present study indicates that sheep may be a reservoir host for granulocytic Ehrlichia infection from one grazing season to the next under natural conditions in Norway.
Highlights
Granulocytic Ehrlichia infection in sheep is endemic in coastal areas of Norway, where the tick Ixodes ricinus is abundant (Øverås 1972, Stuen 1997)
** both animals were in the same pool of blood that gave positive result by inoculation signs of E. phagocytophila infection, nor any seroconversion within one month after inoculation, and Ehrlichia could not be found by either blood smear evaluation or polymerase chain reaction (PCR) technique
In flock A, 2 animals were found positive by blood smear evaluation both before and after lambing, but only one of these was found positive on both samplings
Summary
Granulocytic Ehrlichia infection in sheep (tickborne fever) is endemic in coastal areas of Norway, where the tick Ixodes ricinus is abundant (Øverås 1972, Stuen 1997). Earlier investigations have shown that Ehrlichia phagocytophila is transmitted transtadially in I. ricinus, and that the rickettsiae may survive for several months in these ticks (MacLeod & Gordon 1933, MacLeod 1936). Earlier observations indicate that nearly 100% of the sheep grazing on Ixodes infested pasture may be infected with granulocytic Ehrlichia (Ogden et al 1998), and that the infection could persist for several months after experimental infection (Foggie 1951, Stuen et al 1998). The purpose of this study was to investigate if sheep grazing on I. ricinus infested pasture were still infected with E. phagocytophila after having been housed indoors during wintertime in Norway
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