Abstract
A histological and histochemical study of the
relationship between the protozoan Theileria parva and
the salivary gland cells of its natural vector, the
tick Rhipicephalus appendiculatus has been made. The
literature relating to this subject is reviewed. As a
basis for examining the possibility of host cell participation in the development of the parasite, the changes
that occur in non -infected glands with the process of
feeding were first examined and results compared with
those obtained with T. parva- infected glands. The
possible function of the different acinar cells is presented. Three types of acini were described in the
female and four in the male. The morphological features
of the cell types described here correspond to those
presented by Till (1961) with the exception of those of
Type IV in males which showed secretory granules in
unfed ticks.
The most likely function of non - granular cells
forming Acinus I in both sexes of R. appendiculatus is
in the ionic balance of the tick haemolymph. In Types
II and III acini, cells (a), (c) and (d) are considered
to secrete cement precursors and a proteolytic enzyme
while (b) cells have a general role in the process of
feeding. In feeding females, Type (e) cells are
thought to be responsible for water secretion. In
feeding males, Types (f) and (g) cells are possibly
related to reproduction.
The association between T. parva and the salivary
gland cells of the vector seems to be parasitic rather
than symbiotic. Morphological changes observed in the
host cell nucleus were associated with loss of nucleic
acid material and a reduction in acid phosphatase
activity. In the host cell cytoplasm, infection was
characterised by an increase of reaction for oxidoreductases and PAS positive material and a disappearance of acid phosphatase and of the tyrosine -rich
secretory granules.
Possible metabolic pathways followed by T. parva
in the process of maturation are indicated and an
ultrastructural study of forms of the parasite in the
salivary glands of unfed and feeding ticks presented.
