Resistance of sheep to laboratory infestations of the tick, Ixodes ricinus.

The development of tick resistance was studied in three one-year-old female Galway cross ewes which received up to three staggered infestations of 100 adult pairs of Ixodes ricinus. Sheep acquired resistance after the first infestation and the ticks showed suppressed feeding and oviposition success. The histology of tick-bite lesions revealed a cellular infiltrate consisting predominantly of neutrophils and this was followed by the infiltration and degranulation of basophils. Mononuclear cells accompanied basophil infiltration and then dominated the cellular infiltrate. Eosinophils infiltrated tick-bite lesions in considerable numbers especially in the tertiary infestation, in which degranulation of mast cells and basophils was also most rapid.