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Natural Ehrlichia phagocytophila transmission coefficients from sheep ‘carriers’ to Ixodes ricinus ticks vary with the numbers of feeding ticks

Published online by Cambridge University Press:  30 July 2002

N. H. OGDEN ,
A. N. J. CASEY ,
N. P. FRENCH ,
K. J. BOWN ,
J. D. W. ADAMS  and
Z. WOLDEHIWET
N. H. OGDEN
Affiliation:
Department of Veterinary Preclinical Science, University of Liverpool, Faculty of Veterinary Science, Brownlow Hill and Crown Street, Liverpool L69 7ZJ, UK
A. N. J. CASEY
Affiliation:
Department of Veterinary Preclinical Science, University of Liverpool, Faculty of Veterinary Science, Brownlow Hill and Crown Street, Liverpool L69 7ZJ, UK
N. P. FRENCH
Affiliation:
Department of Veterinary Clinical Science and Animal Husbandry, University of Liverpool, Faculty of Veterinary Science, Leahurst, Neston, South Wirral CH64 7TE, UK
K. J. BOWN
Affiliation:
Department of Veterinary Preclinical Science, University of Liverpool, Faculty of Veterinary Science, Brownlow Hill and Crown Street, Liverpool L69 7ZJ, UK
J. D. W. ADAMS
Affiliation:
Department of Veterinary Clinical Science and Animal Husbandry, University of Liverpool, Faculty of Veterinary Science, Leahurst, Neston, South Wirral CH64 7TE, UK
Z. WOLDEHIWET
Affiliation:
Department of Veterinary Pathology, University of Liverpool, Faculty of Veterinary Science, Leahurst, Neston, South Wirral CH64 7TE, UK
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Abstract

In a longitudinal study in a UK upland site, 38% of adult sheep were detected as infected with the tick-borne bacterium Ehrlichia phagocytophila by PCR of blood samples. Infection prevalence declined significantly with sheep age but varied significantly and non-linearly with the number of adult Ixodes ricinus ticks feeding per sheep. These findings suggested that under conditions of natural repeated tick-borne challenge sheep remain partially susceptible to re-infections, but the likelihood of re-infection depended on the numbers of feeding ticks. Transmission efficiency from sheep to immature ticks also varied significantly and non-linearly with the number of adult ticks feeding per sheep: transmission efficiency was almost zero in sheep with low adult tick infestations rising to 30% at certain levels of adult tick infestation. Infection intensity in infected engorged immature ticks also varied with the number of adult ticks feeding per sheep, but neither prevalence nor intensity of infection in engorged ticks were related to sheep blood PCR result. These findings suggest that variation in the numbers of ticks feeding per sheep may influence E. phagocytophila transmission by direct effects on transmission at the tick–host interface.

Keywords

Ehrlichia phagocytophilaIxodes ricinussheeptransmission
Type
Research Article
Information
Parasitology , Volume 124 , Issue 2 , February 2002 , pp. 127 - 136
Copyright
2002 Cambridge University Press

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