Livestock, pathogens, vectors, and their environment: a causal inference-based approach to estimating the pathway-specific effect of livestock on human African trypanosomiasis risk

Livestock are important reservoirs for many diseases, and investigation of such zoonoses has long been the focus of One Health research. However, the effects of livestock on human and environmental health extend well beyond direct disease transmission. In this retrospective ecological cohort study we use pre-existing data and methods derived from causal inference and spatial epidemiology to estimate three hypothesized mechanisms by which livestock can come to bear on human African trypanosomiasis (HAT) risk: the reservoir effect, by which infected cattle and pigs are a source of infection to humans; the zooprophylactic effect, by which preference for livestock hosts exhibited by the tsetse fly vector of HAT means that their presence protects humans from infection; and the environmental change effect, by which livestock keeping activities modify the environment in such a way that habitat suitability for tsetse flies, and in turn human infection risk, is reduced. We conducted this study in four high burden countries: at the point level in Uganda, Malawi, and Democratic Republic of Congo (DRC), and at the county-level in South Sudan. Our results indicate cattle and pigs play an important reservoir role for the rhodesiense form (rHAT) in Uganda, however zooprophylaxis outweighs this effect for rHAT in Malawi. For the gambiense form (gHAT) we found evidence that pigs may be a competent reservoir, however dominance of the reservoir versus zooprophylactic pathway for cattle varied across countries. We did not find compelling evidence of an environmental change effect.

Oxidative Phosphorylation Is Required for Powering Motility and Development of the Sleeping Sickness Parasite Trypanosoma brucei in the Tsetse Fly Vector

African trypanosomes cause disease in humans and their livestock and are transmitted by tsetse flies. The insect ingests these parasites with its blood meal, but to be transmitted to another mammal, the trypanosome must undergo complex development within the tsetse fly and migrate from the insect's gut to its salivary glands.

‘Where are the dead flies!’: perceptions of local communities towards the deployment of Tiny Targets to control tsetse in the Democratic Republic of the Congo

The National Programme for the control of human African trypanosomiasis in Democratic Republic of Congo includes a large-scale vector control operation using Tiny Targets. These are small panels of insecticide-impregnated cloth that are deployed in riverine habitat where tsetse flies concentrate. The effectiveness of Tiny Targets depends partly on acceptance by local communities. In 2018, we conducted research to explore the perception and acceptability of Tiny Targets in two different village clusters where Tiny Targets had been deployed by the local community or external teams. We conducted fourteen focus group discussions and seven semistructured interviews in three villages from each cluster in the Yasa Bonga health zone. Our findings showed that acceptability was better in the cluster where communities were involved in the deployment of Tiny Targets. Also in this cluster, awareness about Tiny Targets was satisfactory and the project was implemented within local customs, which promoted a positive perception of Tiny Targets and their benefits. In the cluster where external teams deployed Tiny Targets, a lack of information and communication, stereotypes applied by communities towards the deployment teams and the impression of inadequate respect for local customs led to anxiety and a misleading interpretation of the purpose of Tiny Targets and negatively influenced acceptability. This study highlights the importance of involving communities for programme acceptance. Our research underlined how awareness campaigns and communication are essential, but also how working within the scope of community social norms and customs are equally important. Prospects for the successful use of Tiny Targets are greater when communities are involved because the use can be adapted to social norms.

Assessment of α-Cypermethrin Pour-On Application and Diminazene Aceturate for Treating Trypanosome-Related Diseases Caused by Tsetse Flies on Cattle in Mô, Togo

The effects of tsetse-transmitted trypanosomosis control in high tsetse flies (Glossina spp.) challenge and trypanocidal drug resistance settings remain poorly understood in Togo owing to poor data coverage on the current disease impact. From March 2014 to November 2017, a database of zoo-sanitary surveys integrating the evolution of disease incidence and intervention coverage made it possible to quantify the apparent effects attributable to the control effort, focused on all sedentary cattle breeds in the 1,000 km² area of Mô in Togo. The strategy involved an initial phase with cross-sectional entomological and parasitological. Then, three times a year, 20% of the bovine animals of the study area received α-cypermethrin pour-on, and infected cattle with poor health (798 cattle in 2014 and 358 in 2017) were individually given diminazene aceturate at 7 mg/kg of body weight. The tsetse density in the area decreased significantly, from 1.78 ± 0.37 in March 2014 before the α-cypermethrin application to 0.48 ± 0.07 in February 2017. The α-cypermethrin pour-on application and diminazene aceturate treatment of cattle led to the largest reduction in disease incidence, from 28.1% in 2014 to 7.8% in 2017, an improvement in hematocrit from 24.27 ± 4.9% to 27.5 ± 4.6%, and a reduction in calf mortality from 15.9 ± 11% to 5.9%. Improved access to these interventions for different types of livestock and maintaining their effectiveness, despite high tsetse (Diptera: Glossinidae) challenges, should be the primary focus of control strategies in many areas of Togo.

Molecular epidemiology of Animal African Trypanosomosis in southwest Burkina Faso

Background: Animal African Trypanosomosis (AAT) is a parasitic disease of livestock that has a major socio-economic impact in the affected areas. It is caused by several species of uniflagellate extracellular protists of the genus Trypanosoma mainly transmitted by tsetse flies: T. congolense, T. vivax and T. brucei brucei . In Burkina Faso, AAT hampers the proper economic development of the southwestern part of the country, which is yet the best watered area particularly conducive to agriculture and animal production. It was therefore important to investigate the extend of the infection in order to better control the disease. The objective of the present study was to assess the prevalence of trypanosome infections and collect data on the presence of tsetse flies. Methods: Buffy coat, Trypanosoma species-specific PCR, Indirect ELISA Trypanosoma sp and trypanolysis techniques were used on 1898 samples collected. An entomological survey was also carried out. Results: The parasitological prevalence of AAT was 1.1%, and all observed parasites were T. vivax . In contrast, the molecular prevalence was 23%, of which T. vivax was predominant (89%) followed by T. congolense (12%) and T. brucei s.l. (7.3%) with a sizable proportion as mixed infections (9.1%). T. brucei gambiense, responsible of sleeping sickness in humans, was not detected. The serological prevalence reached 49%. Once again T. vivax predominated (86.2%), but followed by T. brucei (9.6%) and T. congolense (4.2%), while 34.6% of positive samples tested positive for at least two trypanosome species. Seven samples, from six cattle and one pig, were found positive by trypanolysis. The density per trap of Glossina tachinoides and G. palpalis gambiensis was about three flies. Conclusions/Significance: Overall, our study showed a high prevalence of trypanosome infection in the area, pointing out an ongoing inadequacy of control measures.

The Development of Wheeled Transportation in Osun Division of Southwestern Nigeria, 1900-1960

Wheeled transportation constituted a single factor that facilitated the incorporation of various African communities into the Europeans’ mercantile economy. In fact, it was an innovation in Africa where people had relied on some navigable waterways in the coastal areas, park animals in the tsetse flies free areas like Northern Nigeria and trekking along foot paths where human head porterage predominated. However, with the advent of the wheeled transportation technology, economic horizon became broader as people were provided with more profitable endeavors to engage themselves with. This essay attempts to analyze the development of wheeled transportation as a factor that was fundamental to the new developments in colonial Osun Division of Southwestern Nigeria. This is in a view to examine the diplomacies that surrounded road and rail construction in the division, Western Regional Government initiatives and the implications of the transportation technology on the divisional economy. The study depends on oral data gathered through interviews and archival materials as well as literatures that were considered relevant to the subject matter. Considering the shift of attention to the production of cash crops which were more profitable compared to the food crops, availability of new jobs as a result of the movement of the trading firms into the division and massive emigration of able bodied men and women in search of 78 Abiodun Ajayi more profitable jobs. There is therefore no doubt that wheeled transportation technology occasioned a transformation that was unprecedented in the colonial economy of Osun Division.

Novel protein candidates for serodiagnosis of African animal trypanosomosis: Evaluation of the diagnostic potential of lysophospholipase and glycerol kinase from Trypanosoma brucei

African trypanosomosis, a parasitic disease caused by protozoan parasites transmitted by tsetse flies, affects both humans and animals in sub-Saharan Africa. While the human form (HAT) is now limited to foci, the animal form (AAT) is widespread and affects the majority of sub-Saharan African countries, and constitutes a real obstacle to the development of animal breeding. The control of AAT is hampered by a lack of standardized and easy-to used diagnosis tools. This study aimed to evaluate the diagnostic potential of TbLysoPLA and TbGK proteins from Trypanosoma brucei brucei for AAT serodiagnosis in indirect ELISA using experimental and field sera, individually, in combination, and associated with the BiP C-terminal domain (C25) from T. congolense. These novel proteins were characterized in silico, and their sequence analysis showed strong identities with their orthologs in other trypanosomes (more than 60% for TbLysoPLA and more than 82% for TbGK). TbLysoPLA displays a low homology with cattle (<35%) and Piroplasma (<15%). However, TbGK shares more than 58% with cattle and between 45–55% with Piroplasma. We could identify seven predicted epitopes on TbLysoPLA sequence and 14 potential epitopes on TbGK. Both proteins were recombinantly expressed in Escherichia coli. Their diagnostic potential was evaluated by ELISA with sera from cattle experimentally infected with T. congolense and with T.b. brucei, sera from cattle naturally infected with T. congolense, T. vivax and T.b. brucei. Both proteins used separately had poor diagnostic performance. However, used together with the BiP protein, they showed 60% of sensitivity and between 87–96% of specificity, comparable to reference ELISA tests. In conclusion, we showed that the performance of the protein combinations is much better than the proteins tested individually for the diagnosis of AAT.

Prevalence of Trypanosoma and Sodalis in Wild Populations of Tsetse Flies: Impact on Sit Programmes for Tsetse Eradication

Tsetse flies, the vectors of African Trypanosoma, have a highly regulated and defined microbial fauna composed of three bacterial symbionts that may have a role to play in the establishment of Trypanosoma infections in the flies and hence, may influence the vectorial competence of the released sterile males. Sodalis bacteria seem to interact with Trypanosoma infection in tsetse flies. Field-caught tsetse flies of ten different taxa and from 15 countries were screened using PCR to detect the presence of Sodalis and Trypanosoma species and their interaction. The results indicate that the prevalence of Sodalis and Trypanosoma varied with country and tsetse species. Trypanosome prevalence was higher in east, central and southern African countries than in west African countries. Tsetse fly infection rates with Trypanosoma vivax and Trypanozoon spp were higher in west African countries, whereas tsetse infection with Trypanosoma congolense and T. simiae, T. simiae (tsavo) and T. godfreyi infection prevalence were higher in east, central and south African countries. Sodalis prevalence was high in Glossina morsitans morsitans and G. pallidipes but absent in Glossina tachinoides. Double and triple infections with Trypanosoma taxa and coinfection of Sodalis and Trypanosoma were rarely observed but it occurs in some taxa and locations. A significant Chi square value (< 0.05) seems to suggest that Sodalis and Trypanosoma infection correlate in Glossina palpalis gambiensis, Glossina pallidipes and Glossina medicorum. Trypanosoma infection significantly increased the density of Sodalis in wild G. m. morsitans and G. pallidipes flies however no significant impact of Sodalis infection on trypanosome density.

Interactions Between Glossina Pallidipes Salivary Gland Hypertrophy Virus and Tsetse Endosymbionts in Wild Tsetse Populations

BackgroundTherefore, tsetse control is considered an effective and sustainable tactic for the control of cyclically transmitted trypanosomosis in the absence of effective vaccines and inexpensive, effective drugs. The sterile insect technique (SIT) is currently used to eliminate tsetse fly populations in an area-wide integrated pest management (AW-IPM) context in Senegal. For SIT, tsetse mass-rearing is a major milestone that associated microbes can influence. Tsetse flies can be infected with micro-organisms, including the primary and obligate Wigglesworthia glossinidia, the commensal Sodalis glossinidius, and Wolbachia pipientis. In addition, tsetse populations often carry a pathogenic DNA virus, the Glossina pallidipes Salivary Gland Hypertrophy Virus (GpSGHV) that hinders tsetse fertility and fecundity. Interactions between symbionts and pathogens might affect the performance of the insect host. MethodsIn the present study, we assessed the possible interaction of GpSGHV and tsetse endosymbionts under field conditions to decipher the bidirectional interactions in different Glossina species. We determined the co-infection pattern of GpSGHV and Wolbachia in natural tsetse populations. We further analyzed the interaction of both Wolbachia and GpSGHV infection with Sodalis and Wigglesworthia density using qPCR. ResultsThe results indicated that the co-infection of GpSGHV and Wolbachia was most prevalent in Glossina austeni and Glossina morsitans morsitans, with an explicit significant negative correlation between GpSGHV and Wigglesworthia infection. GpSGHV infection levels of more than 104 were not observed when Wolbachia infection was present at high density (>108.5), suggesting a potential protective role of Wolbachia against GpSGHV. ConclusionThe result indicates that Wolbachia infection might protect tsetse fly against GpSGHV and the interactions between the tsetse host and its associated microbes are dynamic, likely species-specific and significant differences may exist between laboratory and field conditions.

Characterization and Tissue Tropism of Newly Identified Iflavirus and Negeviruses in Glossina morsitans morsitans Tsetse Flies

Tsetse flies cause major health and economic problems as they transmit trypanosomes causing sleeping sickness in humans (Human African Trypanosomosis, HAT) and nagana in animals (African Animal Trypanosomosis, AAT). A solution to control the spread of these flies and their associated diseases is the implementation of the Sterile Insect Technique (SIT). For successful application of SIT, it is important to establish and maintain healthy insect colonies and produce flies with competitive fitness. However, mass production of tsetse is threatened by covert virus infections, such as the Glossina pallidipes salivary gland hypertrophy virus (GpSGHV). This virus infection can switch from a covert asymptomatic to an overt symptomatic state and cause the collapse of an entire fly colony. Although the effects of GpSGHV infections can be mitigated, the presence of other covert viruses threaten tsetse mass production. Here we demonstrated the presence of two single-stranded RNA viruses isolated from Glossina morsitans morsitans originating from a colony at the Seibersdorf rearing facility. The genome organization and the phylogenetic analysis based on the RNA-dependent RNA polymerase (RdRp) revealed that the two viruses belong to the genera Iflavirus and Negevirus, respectively. The names proposed for the two viruses are Glossina morsitans morsitans iflavirus (GmmIV) and Glossina morsitans morsitans negevirus (GmmNegeV). The GmmIV genome is 9685 nucleotides long with a poly(A) tail and encodes a single polyprotein processed into structural and non-structural viral proteins. The GmmNegeV genome consists of 8140 nucleotides and contains two major overlapping open reading frames (ORF1 and ORF2). ORF1 encodes the largest protein which includes a methyltransferase domain, a ribosomal RNA methyltransferase domain, a helicase domain and a RdRp domain. In this study, a selective RT-qPCR assay to detect the presence of the negative RNA strand for both GmmIV and GmmNegeV viruses proved that both viruses replicate in G. m. morsitans. We analyzed the tissue tropism of these viruses in G. m. morsitans by RNA-FISH to decipher their mode of transmission. Our results demonstrate that both viruses can be found not only in the host’s brain and fat bodies but also in their reproductive organs, and in milk and salivary glands. These findings suggest a potential horizontal viral transmission during feeding and/or a vertically viral transmission from parent to offspring. Although the impact of GmmIV and GmmNegeV in tsetse rearing facilities is still unknown, none of the currently infected tsetse species show any signs of disease from these viruses.