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Title: Ultrastructural observations on host-parasite relationships of Theileria annulata and Theileria parva in vitro
Author: Jura, Walter G. Z. O.
ISNI:       0000 0001 3593 6229
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1983
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Host-parasite interactions of Theileria annulata and T. parva in vitro have been investigated in this thesis. An in situ ultrastructural study of sporogenic development of T. annulata in whole salivary glands from infected, 3-day fed H. anatolicum anatolicum ticks is described. It depicts sporogony as involving continuous growth and differentiation of a single sporont syncytium and appears to suggest that the original ramifying parasite mass eventually gives rise to smaller units, with one or more nuclei, from which sporozoites bud off by schizogony. T. annulata sporozoites measure an average of 0.9 μ m long, 0.8 μ m broad and possess a limiting unit membrane; an ovoid, non-chromocentric and anucleolate nucleus; double-membraned, acristate mitochondria; varying numbers of rhoptries, which together with the polar ring, form the apical complex; and numerous, loosely scattered ribosomal particles. Penetration of lymphocytes by T. annulata sporozoites, as observed by light and electron microscopy in an in vitro culture system, is achieved as early as five minutes of incubation. The sporozoites invade target bovine lymphoid cells base first, the orientation which is dependent on the presence of receptors on the target cell plasmalemma and complementary recognition sites on the basal aspect of the parasite. The receptors have been shown to be susceptible to lysis by trypsin, and are most likely glycoproteins. The invasion of lymphoid cells and the interiorisation of T. annulata sporozoites is actively achieved by the parasite and is an energy-dependent process which is markedly influenced by temperature. The sporozoites are endowed with intact functional metabolic energy pathways, and thus independently generate the ATP required for their invasive activities culminating in intracellular localisation. T. annulata sporozoites interiorise by a deepening invagination of the host lymphocyte plasmalemma which remains intact throughout the entry process and only fragments when the parasite is intracellular. T. annulata sporozoites form pellicular projections. It is believed that such localised pellicular distortions, following a firm parasite- lymphocyte membrane attachment, during active entry by a sporozoite could result in the invagination of host lymphocyte plasma membrane. The interiorised sporozoites, while they dedifferentiate into trophozoites, feed and transform into schizonts, are concomitantly subjected to host lysosomal activity. Viable developing trophozoites do not fuse with lysosomal vesicles, thereby circumventing enzymatic digestion. Failure of lysosomal fusion is attributed to structural alterations accompanying the transformation of interiorised T. annulata sporozoites into trophozoites. Developing intracellular T. annulata and T. parva parasites provoke blastoid transformation of host lymphoid cells by insinuating gene fractions of their DNA. The nuclear envelope-derived annulate lamellae are believed to be a transcription product representing a species of mRNA and function in reciprocal communication of cyclical events in the host nucleus to Theileria schizonts so that through their degradation and assimilation, schizonts are able to monitor host cell chromosomal changes. The influence of Theileria on host replicative machinery is illustrated in a lymphosarcomatous cell line (BL-20) superinfected by T. annulata where the parasite appears to take over control of the host cell replicative mechanism. Light microscope autoradiography using tritiated thymidine demonstrated that Theileria schizonts synthesise their DNA during the G2 phase of host cell interphase stage and replicate their nuclei during the prometaphase stage of host cell cycle. The transformed cells, although susceptible to superinfection by a homologous Theileria species, cannot support the establishment of such interiorised sporozoites as schizonts. The interference is believed to be achieved by the incumbent schizont by blocking host cell gene sites.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Microbiology