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Title: Trypanosomiasis : molecular diagnosis of Trypanosoma evansi infection and endotoxaemia during Trypanosoma brucei rhodesiense infection
Author: Aboubaker, Eltayb Abdelwahab Mohamed
ISNI:       0000 0004 6353 2311
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 2017
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Two aspects of trypanosomiasis have been investigated in this study. First, molecular methods were applied to the diagnosis of T.evansi in camels in South Libya. The aim of the study was to determine if FTA card blood sampling and PCR amplification could detect parasites and this be used as tool for diagnosis and epidemiology. Targeted samples of 70 camels were identified on the basis of symptoms of infection and blood was collected on FTA cards. PCR primers and conditions for the amplification of T.evansi DNA were developed on the basis of the literature and a positive control clone grown in the laboratory. The assay found 84.3% of camel samples positive using TBR primers (177bp amplicon) and ITS nested primers (611-1513bp amplicons). This result demonstrated that Surra is endemic in this area, and that T.evansi was the species that was involved. The ITS and TBR loci in the parasites identified in Libya were almost identical to those previously reported in the genbank database, though with some polymorphisms. Dullness and emaciation were the clinical signs of camels infected by trypanosomes, and these two symptoms were significantly related to the 1200bp ITS nested PCR amplicon. These two symptoms can be thus used as a sign an initial diagnosis of T.evansi infection in camels. The second aspect of trypanosomiasis studied was the occurrence of endotoxaemia in infection. The first part of this research investigated endotoxin levels in clinical human African trypasnosomiasis using the Limulus Amoebocyte lysate assay. Endotoxin levels were significantly increased over control individuals in the plasma of T.b.rhodesiense patients. This endotoxaemia was unrelated to infection duration, parasitaemia or clinical stage but resolved after clearance of parasites by drug treatment. In the cerebrospinal fluid there was no significant difference in endotoxin level between early and late stage cases and no relationship to parasite loads. It is argued on the basis of the data that endotoxaemia in trypanosomiasis most likely results from increases in permeability of the gut to endotoxins from gram negative enter bacteria. This conclusion was further supported from a study using cell culture adapted T.brucei and secreted products which gave no evidence of any endotoxin activity. Also samples of an acute experimental mouse infection with T.brucei gave no endotoxin activity, suggesting that this phenomenon requires a more chronic infection in mice. No relationships were found between plasma or CSF endotoxin levels to neurological signs of infection. However the presence of a gross inflammatory clinical symptom, splenomegaly, was associated with endotoxaemia and the concentrations of 3 plasma cytokines associated with the immune response in trypanosome infection were associated with correlated to plasma endotoxin levels. In order to determine the nature of the endotoxin activity, a biosensor cell assay for LPS was used, based on human embryonic kidney cells transfected with TLR4/MD3 and a NF-κB induced alkaline phosphatase reporter gene. This assay revealed low or undetectable levels of LPS in clinical samples from T.b.rhodesiense patients, in mouse samples from T.b.brucei infections and in vitro cultured trypanosomes. This suggests that either the endotoxin activity detected using the LAL assay is an unconventional endotoxin signalling via a TLR4 independent pathway or that the human plasma was in some way toxic to the reporter cell and this requires further investigation. In conclusion, this study has provided the first clear evidence of an association of endotoxaemia and inflammatory responses in clinical African trypansomiasis and helps resolve the question of whether endotoxaemia is a parasite or host-microbiota related phenomenon.
Supervisor: Not available Sponsor: Libyan Embassy ; London
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Trypanosoma ; Trypanosoma brucei ; Trypanosomiasis ; Endotoxemia