Ixodes ricinus, the sheep tick: ecology and disease

Webster, Katherine Anne (1987) Ixodes ricinus, the sheep tick: ecology and disease. PhD thesis, University of Glasgow.

Abstract

Relevant literature was reviewed and the ecology of the sheep tick, Ixodes ricinus and associated disease problems studied in south west Scotland. The development and maintenance of a colony of I.ricinus in the laboratory to provide tick-borne fever (T.B.F.) infected and T.B.F. free ticks for electron microscopic and tick pyaemia transmission studies was described. Additionally development times for each instar were measured during routine colony maintenance. The activity and development of I.ricinus was measured over three years at two sites on Ayrshire sheep farms by blanket drags of pasture areas and tick counts on sheep. Engorged stages were placed in nylon mesh tubes under the vegetation mat, in order to monitor development to subsequent stages. In all instances development to the next instar occurred during the late summer or autumn. Activity patterns varied from year to year with a prolonged period of summer activity in 1984, a bimodal distribution in 1985 and a single spring peak in 1986. Meteorological data was recorded in an attempt, only partially successful, to apply the model devised by Gardiner and Gettinby (1983) to data from these studies. A postal questionnaire was circulated to 300 farmers in Ayrshire and Argyll concerned with seasonal and local distribution of ticks, disease problems and control measures. The replies indicated a high tick incidence in Argyll and marked disease problems in certain regions of Ayrshire where ticks were present. Several of the farms were investigated in more detail by farm visits and examination of blood samples. Experimental tick-borne fever (T.B.F.) infections induced in young lambs were monitored by measurement of rectal temperatures, haematology, assessment of parasitaemias and neutrophil function tests. The classical febrile response accompanied by acute parasitaemia, lymphocytopaenia and followed by neutropaenia was recorded. Additionally an impairment of neutrophil function was demonstrated prior to the neutropaenia using an in vitro assay of neutrophil function. A counter immunoelectrophoresis (CIE) test was developed to detect antibodies produced after T.B.F. infection. Sera from experimental infections in lambs and goats were used to determine the interval after primary infection before antibody could be detected, this was shown to be 9-11 days post intravenous inoculation of the organism and the period of persistence 6-10 weeks in lambs. Four hundred and thirteen ovine field sera obtained from sheep of all ages from predominantly tick infested regions of Scotland and the north of England were tested with a positive rate of 18.2%. When CIE serology was coupled with conventional examination of blood smears the detection rate for ovine T.B.F. was doubled. Additionally, antibodies were detected in a number of sera from cattle, goats and deer using CIE. An electron microscopic technique was developed to demonstrate C.phagocytophila in I.ricinus. This technique was subsequently applied to ticks collected from one sheep farm in an attempt to estimate the level of infection. C.phagocytophila infection was absent from larvae, while 44% of nymphae were infected and 32 % of adults. This result supports the previous finding that transovarial transmission does not occur. Recent publications have indicated that an important aspect of T.B.F. infection in lambs is the associated immunosuppression which allows invasion of secondary pathogens, notably Staphylococcus aureus the causal agent of tick pyaemia. Several experiments were therefore conducted in lambs and mice to examine this aspect. In mice B-lymphocytes were depressed using cyclophosphamide (CY) [ to mimic one aspect of T.B.F. infection] and the mice subsequently challenged with Staphylococcus aureus administered by various routes. Death rates , lesion formation and bacteriological isolations were greater in mice pre-treated with CY. The experiment was repeated in young lambs using T.B.F. rather than CY as a potential suppressive agent. Five days after T.B.F. infection, S.aureus contaminated ticks were allowed to attach and engorge upon the lambs. At necropsy, abscesses from which S.aureus was recovered, were present in the lungs and livers of lambs given T.B.F. and exposed to contaminated ticks, but not in controls which were only exposed to contaminated ticks. This is believed to be the first experimental production of tick pyaemia in lambs using the sheep tick I.ricinus as a mechanical vector of S.aureus.Control of I.ricinus is traditionally by whole body immersion in acaricidal preparations; however more recently synthetic pyrethroid pour-on formulations have been available. Field trials to assess the efficacy of two synthetic pyrethroid pour-on products are described. Tick counts were performed on treated and control lambs and hoggs, disease levels assessed and other effects of the treatment monitored. Results indicate a degree of tick control was achieved , but disease problems still occurred.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Entomology, parasitology.
• Colleges/Schools: College of Medical Veterinary and Life Sciences
• Supervisor's Name: Mitchell, Dr. G.B.B.
• Date of Award: 1987
• Depositing User: Enlighten Team
• Unique ID: glathesis:1987-73947
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 14 Jun 2019 08:56
• Last Modified: 09 Jun 2021 15:52
• URI: https://theses.gla.ac.uk/id/eprint/73947