Mutugi, Marion Wanjiku

2018-03-29T12:19:11Z

2018-03-29T12:19:11Z

1993

The work described ill this thesis examined 44 stocks of T. evansi, 41 of which were isolated from camels in various areas of Kenya. These tiypanosomes had a mean length of 25.5 + 2.8 (Tin a mean prepatent period of 4.7 + 3.4 days and fulfilled the classical criteria of this species in regard to these two parameters. Initially, the sensitivity of these tiypanosome stocks was determined to four trypanocidal drugs active against T. evansi. The 44 stocks exhibited resistance to Berenil (57%), Samorin (7%), suramin (22%) and Trypacide (18%). It was noted that although Bcrcnil is not recommended for use in camels due to its toxicity, more than half of the stocks were resistant to this drug, flic malic enzyme |ialtcms of these stocks were determined to investigate jiossible correlation with resistance to the trypanocidcs used. Most of the stocks (66%) possessed malic isoenzyme pattern II (66%), although patterns X (23%), IV (7%) and VII (5%) were also observed. Malic enzyme patterns IV and X had not been identified previously in this tiypanosome species. No linkage was found between any of these patterns and resistance to the four drugs.

Further work concentrated on three trypanosome stocks which were highly resistant, of intermediate resistance or sensitive to the action of suramin. Investigations on the effect of tiypanosome inoculum and timing of suramin administration in obtaining cures in T. evansi infected mice were carried out The time of administration after infection was shown to be an important factor that influenced the outcome of suramin treatment. Mice which were treated immediately after infection had higher cure rates than those treated at the onset of parasitaemia. This was observed particularly in a tiypanosome stock normally resistant to suramin at a dose rate of 160 mg/kg; if treatment was administered immediately after infection, most of the infected mice were cured. Except in the highly resistant stock, the role of trypanosome inoculum was not as important as timing of treatment in determining cures. The influence of both high tiypanosome inocula and late administration of drug on failure of treatment was probably due to the opportunity provided for trypanosomes to invade the central nervous system. It is thus important to closely monitor animals that are exposed to trypanosomiasis in order to treat promptly those that are infected and thus increase the treatment success rate.

This study also investigated the interaction of suramin-sensitive and resistant trypanosomes in mixed infections. Drug-sensitive parasites were shown to interfere with the establislunent of infection with the drug-resistant trypanosomes. Interference was not observed when both stocks were inoculated simultaneously. When a sensitive stock was inoculated first and allowed to establish infection in mice, subsequent inoculation of (he resistant stock and treatment with suramin resulted in up to 60% cures suggesting that the resistant trypanosomes had not been able to establish infection in all instances. To a lesser extent, interference was observed in rats whereby treatment with suramin resulted in suppression of parasitaemia. If mice were inoculated with the resistant stock first, a tcni|xirary suppression of parasitaenria resulted. No interference was observed in the establislunent of infection in rats.

Suramin sensitivities were determined in clones derived from four trypanosome stocks. All four stocks were shown to comprise clones with a wide spectrum of suramin sensitivities. Two of the cloned trypanosome stocks which were sensitive to 0.01 mg/kg of suramin were used in experiments to induce resistance by the administration of sub-curative doses in infected mice. The resistant clones were compared with their sensitive parents and shown to have slower growth rates in rats. This slower growth rate was especially marked in one stock of tryjianosomes which had the higher level of resistance. Both the interference phenomenon and the slower growth rale of resistant trypanosomcs may lie imjiortant as a means by which resistant trypanosomes are selected out in mixed infections under field conditions, thereby limiting the potential spread of suramin resistance.

Suramin resistance at the molecular level was investigated by comparing the DNA of suraminresistant stocks of 7". evansi with (hat of the parent slocks from which they were derived. Endonucleasedigested trypanosome DNA was separated by electrophoresis and hybridised with a ribosomal probe and a pglycoprolein probe. Hybridisation results showed that there were differences in DNA banding patterns which could be associated with suramin resistance. This preliminary study suggests that suramin resistance may be correlated to sjiecific DNA banding patterns. These DNA differences may have a potential as markers for suramin resistance in T. evansi.

http://hdl.handle.net/1842/29291

The University of Edinburgh

Annexe Thesis Digitisation Project 2018 Block 17

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Studies on suramin resistance in Kenyan stocks of Trypanosoma evansi (Steel, 1885 Balbiani, 1888)

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PhD Doctor of Philosophy