Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)




Previous studies have demostrated that host acquired resistance resulted in reduced numbers of engorged ticks, restricted engorgement, reduced numbers and viability of ova, longer duration of feeding, and in some instances, the death of the tick. It is currently not understood how ticks are adversely affected by feeding on hosts expressing acquired tick resistance.

Examination of the midgut and diverticulae of adult female Amblyomma americanum allowed to engorge on guinea pigs acquiring and expressing tick resistance revealed changes in the gut epithelium as well as in the cellular composition of the blood meal. Engorging females were removed from hosts at various intervals during the course of four experimental infestations. Tissue specimens were obtained from defined areas of the tick gut, placed into Karnovsky's fixative, and embedded in epon-araldite resin. Sections were viewed with either a light microscope or transmission electron microscope.

The midgut and deverticulae were lined by a pseudostratified epithelium consisting of six cell types which rested on a basal lamina. Outside the basal lamina was a network of visceral muscle cells. As feeding progressed, the gut epithelium underwent significant changes that could be correlated with uptake and digestion of the blood meal. The processes of pinocytosis and phagocytosis were evident along the lumenal borders of the digestive cells. Numerous cellular organelles and cytoplasmic inclusions associated with intracellular digestion were present in the cytoplasm.

Gut tissues from adults fed on guinea pigs expressing tick resistance showed morphological changes that were indicative of cellular damage. Basophils, eosinophils, and granules derived from these cells were present in the gut lumenal contents and were ingested by the epithelial cells of the digestive tract. Death in situ of the ticks could be correlated with epithelial cell damage, and the presence of eosinophils, basophils, or their respective granules.

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