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University of Edinburgh (1993)

Population diversity in Theileria annulata in Tunisia

Ben Miled, Leila

Titre : Population diversity in Theileria annulata in Tunisia

Auteur Ben Miled, Leila

Université de soutenance : University of Edinburgh

Grade : PhD Doctor of Philosophy 1993

Résumé
Tropical theileriosis, caused by the haemoprotozoan parasite Theileria annulata, is one of the major — ;ats to cattle health in Tunisia. The aim ofthe study described in this thesis was to assess the extent ofdiversity —T. annulata parasite populations from within a single country in order to provide a better understanding ofthe Semiology ofthe disease and biology ofthe parasite. The work also provided useful background information raccine development studies in Tunisia. Different T. annulata stocks, isolated from differentbioclimatic zones in Tunisia were characterised using ^noclonal antibodies (MAbs), isoenzyme and DNA analyses and compared with each otherand with a number of =ognised laboratory stocks from othertheileriosis endemic areas ofthe world. The study comprises seven chapters. In the first, an introduction to the literaturedescribing the parasite T. lulata and the disease it causes are presented and the epidemiology of tropical theileriosis is discussed with —ticular regard to the situation in Tunisia. Finally an overview on diversity in protozoan parasites, including lileria, is given to emphasise the rationale behind the present study. The next chapter details how the biological material, including 51 field isolates, was generated for the -se parasite life-cycle stages, sporozoites, piroplasms and schizonts. In the third chapter the production ofantischizont MAbs and their use as immunological makers to reveal ■Terences between stocks of T. annulata is described. The fourth chapter demonstrates the use ofa biochemical marker, glucose phosphate isomerase isoenzyme study diversity in T. annulata isolated in Tunisia. In the fifth chapter, DNA probes generated from a genomic library of T. annulata piroplasms were tlysed to select appropriate markers for characterisation of genomic variants ofthe parasite. One ofthese, the ■T17 probe, was used to define five variants which were obtained as cloned infected lymphoblastoid cell lines, ■striction mapping of these variants showed that deletion, point mutation and translocation might be common :nts in the T. annulata genome. It was also found that part of this probe comprises a cysteine protease gene ich possesses some homology with a T. parva cysteine protease gene. The sixth chapter analyses the diversity in the stocks isolated from Tunisia using the markers selected and scribed in the previous chapters. The diversity existing between isolates was analysed at several levels ; within -lates from one country, one bioclimatic zone, one site of isolation, one farm or, finally one animal and the ults show that tremendous polymorphism exists. Experiments performed to assess the reliability ofthe methods :d are also presented. In the final chapter, investigations into the infectivity, virulence and immunity stimulated by individual ■ned infected cell lines compared to a mixture ofthe same clones are described. The implications ofthe results -this study are discussed in relation to the selection ofappropriate vaccines for use in the field. In addition, DNA -m parental cell lines and the clones derived from them, obtained by tick transmission from the calves used in the ectivity study were analysed by southern blotting using DNA probes. The results showed that parasite clones of vel, non-parental genotype were obtained in the progeny and recombination between the parental characters was monstrated. By localising the different DNA probes on the chromosome of T. annulata it was possible to show it recombination was due either to independent assortment between non-homologous chromosomes or crossing er between homologous chromosomes. These results give evidence for sexual reproduction in 7 ! annulata. is, together with the findings that deletion, point mutation and translocation might occur in the T. annulata nome give a new approach to studying genetics in Theileria and help to explain the marked polymorphism found this study. •>T/88

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