Hypersensitivity skin testing of lambs infested with the biting louse (Bovicola ovis) (abstract)

Authors: Phegan MD, Bany JS, Pfeffer A, Osborn PJ
Publication: New Zealand Veterinary Journal, Volume 42, Issue 2, pp 76, Apr 1994
Publisher: Taylor and Francis

Animal type: Livestock, Production animal, Ruminant, Sheep
Subject Terms: Inflammation, Integument/skin/wool/hair/fur/feather, Disease/defect, Diagnostic procedures, Immune system/immunology, Parasites - external
Article class: Abstract

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Abstract: Cockle, a defect of lamb`s pelts, has recently been shown to be associated with infestation of lambs with the louse Bovicola ovis. The mechanisms by which infestation with the louse leads to cockle are not known, but immunological hypersensitivity has been suggested. The objectives of our work are to determine if lambs respond immunologically to lice and, if so, whether hypersensitivity occurs. Preliminary results are presented here.
Passive cutaneous anaphylaxis (PCA) testing was carried out by injecting 0.2 ml of serum from individual lambs intradermally into a louse-naive lamb (reared louse-free from birth), and injecting intravenously Evan`s blue dye and a soluble extract from crushed lice 72 hours later. Skin reactions were then measured 1 hour later. Positive reactions were detected with sera from 2/7 lambs with louse infestation and cockle, 1/5 lambs with louse infestation without cockle and 0/6 louse-naive lambs.
Active hypersensitivity skin testing was done monthly from May to October 1993 using lambs from three groups: infested with lice from birth: infested from 3 months of age (from December 1993): or louse-naive. Testing involved intradermal injection of 0.2 ml of soluble louse extract (100 µg/ml protein) and measuring reactions at 1, 5, 24, 48, 72 and 96 hours later. Typically, louse-naive lambs showed mild reactions to the louse extract that persisted up to 48 hours after injection. The lambs infested with lice showed significantly greater reactions compared to the louse-naive lambs from 5 hours after injection and the reactions persisted relatively undiminished to 96 hours. Histologically, the skin reactions of the louse-infected lambs were characterised by eosinophil and mononuclear leucocyte infiltration of the dermis and epidermal hyperplasia.
The PCA and active skin testing results are the first reported evidence for immunological responses of lambs to Bovicola ovis. The PCA test demonstrated reaginic antibody in the sera of some lambs with lice and/or cockle. This supports the possibility of immediate hypersensitivity in response to louse infestation. Further, active skin testing demonstrated a delayed hypersensitivity-like response. More work is required to determine the role of either type of hypersensitivity in the development of cockle.

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