Some Aspects of Chemoprophylaxis Against Trypanosoma congolense

[摘要] This thesis is concerned with investigating two aspects of the use of isometamidium chloride (Samorin, May and Baker, Dagenham) as a chemoprophylactic drug. Firstly, twentyfour Boran cattle were injected with 1 mg/kg isometamidium chloride to investigate the duration of drug-induced prophylaxis against infection by metacyclic forms of Trypanosome congolense, and to determine if specific antibody responses to the organisms were mounted by animals under chemoprophylactic cover. Complete protection against either single challenge by five tsetse infected with Trypanosoma congolense, or repeated challenge at monthly intervals by five tsetse, lasted for 148 days or approximately five months. Even at six months post treatment, two-thirds of the cattle were still resistant to challenge with either trypanosome-infected tsetse, or titrated doses of in vitro derived metacyclic forms of T. congolense (5x10e2 to 5 x 10e5 organisms), innoculated intradermally. No animal which resisted infection developed either detectable skin reactions at the site of the metacyclic innoculation or produced trypanosome-specific antibodies. It was concluded that drug levels in the skin were effective at preventing trypanosome multiplication, thus preventing the development of parasitaemia or priming of the hosts' immune system. Secondly, the local tissue toxicity of isometamidium chloride and its dextran complex were investigated. Four Boran cattle/ cattle were injected at different sites with 2% and 4% isometamidium chloride or 2% isometamidium-dextran complex. Sequential slaughter at 7, 28 and 56 days post injection was carried out and the innoculation sites examined for changes in gross pathology and histology. Both 2% and 4% isometamidium chloride given at a dose of 1mg/kg/injection site resulted in severe tissue damage which progressed from a necrotic, oedematous, haemorrhagic lesion at day 7 to extensive fibrosis by day 56. Isometamidium-dextran complex produced a limited well encapsulated lesion and was safe to inject subcutaneously.

[发布机构] University:University of Glasgow

[关键词] Veterinary science