Evidence of the absence of human African trypanosomiasis in two northern districts of Uganda: Analyses of cattle, pigs and tsetse flies for the presence of Trypanosoma brucei gambiense

AbstractBackgroundLarge-scale control of sleeping sickness has led to a decline in the number of cases of Gambian human African trypanosomiasis (g-HAT) to <2000/year. However, achieving complete and lasting interruption of transmission may be difficult because animals may act as reservoir hosts for T. b. gambiense. Our study aims to update our understanding of T. b. gambiense in local vectors and domestic animals of N.W. Uganda.MethodsWe collected blood from 2896 cattle and 400 pigs and In addition, 6664 tsetse underwent microscopical examination for the presence of trypanosomes. Trypanosoma species were identified in tsetse from a subsample of 2184 using PCR. Primers specific for T. brucei s.l. and for T. brucei sub-species were used to screen cattle, pig and tsetse samples.ResultsIn total, 39/2,088 (1.9%; 95% CI=1.9-2.5) cattle, 25/400 (6.3%; 95% CI=4.1-9.1) pigs and 40/2,184 (1.8%; 95% CI=1.3-2.5) tsetse, were positive for T. brucei s.l.. Of these samples 24 cattle (61.5%), 15 pig (60%) and 25 tsetse (62.5%) samples had sufficient DNA to be screened using the T. brucei sub-species PCR. Further analysis found no cattle or pigs positive for T. b. gambiense, however, 17/40 of the tsetse samples produced a band suggestive of T. b. gambiense. When three of these 17 PCR products were sequenced the sequences were markedly different to T. b. gambiense, indicating that these flies were not infected with T. b. gambiense.ConclusionThe absence of T. b. gambiense in cattle, pigs and tsetse accords with the low prevalence of g-HAT in the human population. We found no evidence that livestock are acting as reservoir hosts. However, this study highlights the limitations of current methods of detecting and identifying T. b. gambiense which relies on a single copy-gene to discriminate between the different sub-species of T. brucei s.l.Author SummaryThe decline of annual cases of West-African sleeping sickness in Uganda raises the prospect that elimination of the disease is achievable for the country. However, with the decrease in incidence and the likely subsequent change in priorities there is a need to confirm that the disease is truly eliminated. One unanswered question is the role that domestic animals play in maintaining transmission of the disease. The potential of cryptic-animal reservoirs is a serious threat to successful and sustained elimination of the disease. It is with the intent of resolving this question that we have carried out this study whereby we examined 2088 cattle, 400 pigs and 2184 tsetse for Trypanosoma brucei gambiense, the parasite responsible for the disease. Our study found T. brucei s.l. in local cattle, pigs and tsetse flies, with their respective prevalences as follows, 1.9%, 6.3% and 1.8%. Further analysis to establish identity of these positives to the sub-species level found that no cattle, pigs or tsetse were carrying the pathogen responsible for Gambian sleeping sickness. Our work highlights the difficulty of establishing the absence of a disease, especially in an extremely low endemic setting, and the limitations of some of the most commonly used methods.

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Trypanosomal variant surface glycoprotein expression in human African trypanosomiasis patients

10.1101/2021.09.09.459620 ◽

2021 ◽

Author(s):

Jaime So ◽

Sarah Sudlow ◽

Abeer Sayeed ◽

Tanner Grudda ◽

Stijn Deborggraeve ◽

...

Keyword(s):

Trypanosoma Brucei ◽

Human African Trypanosomiasis ◽

Antigenic Variation ◽

Surface Glycoprotein ◽

Variant Surface Glycoprotein ◽

Tsetse Flies ◽

African Trypanosomiasis ◽

Trypanosoma Brucei Gambiense ◽

Terminal Domain ◽

Human Infections

AbstractTrypanosoma brucei gambiense, an extracellular protozoan parasite, is the primary causative agent of human African Trypanosomiasis. T. b. gambiense is endemic to West and Central Africa where it is transmitted by the bite of infected tsetse flies. In the bloodstream of an infected host, the parasite evades antibody recognition by altering the Variant Surface Glycoprotein (VSG) that forms a dense coat on its cell surface through a process known as antigenic variation. Each VSG has a variable N-terminal domain that is exposed to the host and a less variable C-terminal domain that is at least partially hidden from host antibodies. Our lab developed VSG-seq, a targeted RNA-seq method, to study VSG expression in T. brucei. Studies using VSG-seq to characterize antigenic variation in a mouse model have revealed marked diversity in VSG expression within parasite populations, but this finding has not yet been validated in a natural human infection. Here, we used VSG-seq to analyze VSGs expressed in the blood of twelve patients infected with T. b. gambiense. The number of VSGs identified per patient ranged from one to fourteen and, notably, two VSGs were shared by more than one patient. Analysis of expressed VSG N-terminal domain types revealed that 82% of expressed VSGs encoded a type B N-terminus, a bias not seen in datasets from other T. brucei subspecies. C-terminal types in T. b. gambiense infection were also restricted. These results demonstrate a bias either in the underlying VSG repertoire of T. b. gambiense or in the selection of VSGs from the repertoire during infection. This work demonstrates the feasibility of using VSG-seq to study antigenic variation in human infections and highlights the importance of understanding VSG repertoires in the field.Author SummaryHuman African Trypanosomiasis is a neglected tropical disease largely caused by the extracellular parasite known as Trypanosoma brucei gambiense. To avoid elimination by the host, these parasites repeatedly replace their dense surface coat of Variant Surface Glycoprotein (VSG). Despite the important role of VSGs in prolonging infection, VSG expression during natural human infections is poorly understood. A better understanding of natural VSG expression dynamics can clarify the mechanisms which T. brucei uses to alter its VSG coat and improve how trypanosomiasis is diagnosed in humans. We analyzed the expressed VSGs detected in the blood of patients with trypanosomiasis. Our findings indicate that a diverse range of VSGs are expressed in both natural and experimental infections.

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Human African trypanosomiasis

Oxford Textbook of Medicine ◽

10.1093/med/9780199204854.003.070810_update_001 ◽

2010 ◽

pp. 1119-1127

Author(s):

August Stich

Keyword(s):

West Africa ◽

East Africa ◽

Trypanosoma Brucei ◽

Human African Trypanosomiasis ◽

Protozoan Parasite ◽

Sleeping Sickness ◽

Tsetse Flies ◽

African Trypanosomiasis ◽

Tropical Africa

Human African trypanosomiasis (HAT, sleeping sickness) is caused by two subspecies of the protozoan parasite Trypanosoma brucei: T. b. rhodesiense is prevalent in East Africa among many wild and domestic mammals; T. b. gambiense causes an anthroponosis in Central and West Africa. The disease is restricted to tropical Africa where it is transmitted by the bite of infected tsetse flies (...

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Human African trypanosomiasis

Oxford Textbook of Medicine ◽

10.1093/med/9780198746690.003.0169 ◽

2020 ◽

pp. 1451-1459

Author(s):

Reto Brun ◽

Johannes Blum

Keyword(s):

Trypanosoma Brucei ◽

Human African Trypanosomiasis ◽

Specific Treatment ◽

Protozoan Parasite ◽

Control Measures ◽

Tsetse Flies ◽

African Trypanosomiasis ◽

Control Programmes ◽

The 1960S ◽

Stage 1

Human African trypanosomiasis (sleeping sickness) is caused by subspecies of the protozoan parasite Trypanosoma brucei. The disease is restricted to tropical Africa where it is transmitted by the bite of infected tsetse flies (Glossina spp.). Control programmes in the 1960s were very effective, but subsequent relaxation of control measures led to recurrence of epidemic proportions in the 1980s and 1990s. Control is now being regained. Untreated human African trypanosomiasis is almost invariably fatal. Specific treatment depends on the trypanosome subspecies and the stage of the disease. Drugs used for stage 1 include pentamidine and suramin, and for stage 2 include melarsoprol, eflornithine, and nifurtimox, but regimens are not standardized, and treatment is difficult and dangerous; all of the drugs used have many side effects, some potentially lethal.

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