The potential economic benefits of controlling trypanosomiasis using waterbuck repellent blend in sub-Saharan Africa.

Trypanosomiasis is a significant productivity-limiting livestock disease in sub-Saharan Africa, contributing to poverty and food insecurity. In this paper, we estimate the potential economic gains from adopting Waterbuck Repellent Blend (WRB). The WRB is a new technology that pushes trypanosomiasis-transmitting tsetse fly away from animals, improving animals' health and increasing meat and milk productivity. We estimate the benefits of WRB on the production of meat and milk using the economic surplus approach. We obtained data from an expert elicitation survey, secondary and experimental sources. Our findings show that the adoption of WRB in 5 to 50% of the animal population would generate an economic surplus of US$ 78-869 million per annum for African 18 countries. The estimated benefit-cost ratio (9:1) further justifies an investment in WRB. The technology's potential benefits are likely to be underestimated since our estimates did not include the indirect benefits of the technology adoption, such as the increase in the quantity and quality of animals' draught power services and human and environmental health effects. These benefits suggest that investing in WRB can contribute to nutrition security and sustainable development goals.

Computational Identification of Master Regulators Influencing Trypanotolerance in Cattle.

African Animal Trypanosomiasis (AAT) is transmitted by the tsetse fly which carries pathogenic trypanosomes in its saliva, thus causing debilitating infection to livestock health. As the disease advances, a multistage progression process is observed based on the progressive clinical signs displayed in the host's body. Investigation of genes expressed with regular monotonic patterns (known as Monotonically Expressed Genes (MEGs)) and of their master regulators can provide important clue for the understanding of the molecular mechanisms underlying the AAT disease. For this purpose, we analysed MEGs for three tissues (liver, spleen and lymph node) of two cattle breeds, namely trypanosusceptible Boran and trypanotolerant N'Dama. Our analysis revealed cattle breed-specific master regulators which are highly related to distinguish the genetic programs in both cattle breeds. Especially the master regulators MYC and DBP found in this study, seem to influence the immune responses strongly, thereby susceptibility and trypanotolerance of Boran and N'Dama respectively. Furthermore, our pathway analysis also bolsters the crucial roles of these master regulators. Taken together, our findings provide novel insights into breed-specific master regulators which orchestrate the regulatory cascades influencing the level of trypanotolerance in cattle breeds and thus could be promising drug targets for future therapeutic interventions.

The molecular and cellular basis of olfactory response to tsetse fly attractants.

Dipteran or "true" flies occupy nearly every terrestrial habitat, and have evolved to feed upon a wide variety of sources including fruit, pollen, decomposing animal matter, and even vertebrate blood. Here we analyze the molecular, genetic and cellular basis of odor response in the tsetse fly Glossina morsitans, which feeds on the blood of humans and their livestock, and is a vector of deadly trypanosomes. The G. morsitans antenna contains specialized subtypes of sensilla, some of which line a sensory pit not found in the fruit fly Drosophila. We characterize distinct patterns of G. morsitans Odor receptor (GmmOr) gene expression in the antenna. We devise a new version of the "empty neuron" heterologous expression system, and use it to functionally express several GmmOrs in a mutant olfactory receptor neuron (ORN) of Drosophila. GmmOr35 responds to 1-hexen-3-ol, an odorant found in human emanations, and also alpha-pinene, a compound produced by malarial parasites. Another receptor, GmmOr9, which is expressed in the sensory pit, responds to acetone, 2-butanone and 2-propanol. We confirm by electrophysiological recording that neurons of the sensory pit respond to these odorants. Acetone and 2-butanone are strong attractants long used in the field to trap tsetse. We find that 2-propanol is also an attractant for both G. morsitans and the related species G. fuscipes, a major vector of African sleeping sickness. The results identify 2-propanol as a candidate for an environmentally friendly and practical tsetse attractant. Taken together, this work characterizes the olfactory system of a highly distinct kind of fly, and it provides an approach to identifying new agents for controlling the fly and the devastating diseases that it carries.

The population genomics of multiple tsetse fly (Glossina fuscipes fuscipes) admixture zones in Uganda.

Understanding the mechanisms that enforce, maintain or reverse the process of speciation is an important challenge in evolutionary biology. This study investigates the patterns of divergence and discusses the processes that form and maintain divergent lineages of the tsetse fly Glossina fuscipes fuscipes in Uganda. We sampled 251 flies from 18 sites spanning known genetic lineages and the four admixture zones between them. We apply population genomics, hybrid zone and approximate Bayesian computation to the analysis of three types of genetic markers: 55,267 double-digest restriction site-associated DNA (ddRAD) SNPs to assess genome-wide admixture, 16 microsatellites to provide continuity with published data and accurate biogeographic modelling, and a 491-bp fragment of mitochondrial cytochrome oxidase I and II to infer maternal inheritance patterns. Admixture zones correspond with regions impacted by the reorganization of Uganda's river networks that occurred during the formation of the West African Rift system over the last several hundred thousand years. Because tsetse fly population distributions are defined by rivers, admixture zones likely represent both old and new regions of secondary contact. Our results indicate that older hybrid zones contain mostly parental types, while younger zones contain variable hybrid types resulting from multiple generations of interbreeding. These findings suggest that reproductive barriers are nearly complete in the older admixture zones, while nearly absent in the younger admixture zones. Findings are consistent with predictions of hybrid zone theory: Populations in zones of secondary contact transition rapidly from early to late stages of speciation or collapse all together.

Neutrophils enhance early Trypanosoma brucei infection onset.

In this study, Trypanosoma brucei was naturally transmitted to mice through the bites of infected Glossina morsitans tsetse flies. Neutrophils were recruited rapidly to the bite site, whereas monocytes were attracted more gradually. Expression of inflammatory cytokines (il1b, il6), il10 and neutrophil chemokines (cxcl1, cxcl5) was transiently up-regulated at the site of parasite inoculation. Then, a second influx of neutrophils occurred that coincided with the previously described parasite retention and expansion in the ear dermis. Congenital and experimental neutropenia models, combined with bioluminescent imaging, indicate that neutrophils do not significantly contribute to dermal parasite control and elicit higher systemic parasitemia levels during the infection onset. Engulfment of parasites by neutrophils in the skin was rarely observed and was restricted to parasites with reduced motility/viability, whereas live parasites escaped phagocytosis. To our knowledge, this study represents the first description of a trypanosome infection promoting role of early innate immunological reactions following an infective tsetse fly bite. Our data indicate that the trypanosome is not hindered in its early development and benefits from the host innate responses with the neutrophils being important regulators of the early infection, as already demonstrated for the sand fly transmitted Leishmania parasite.

Tsetse Flies (Glossina) as Vectors of Human African Trypanosomiasis: A Review.

Human African Trypanosomiasis (HAT) transmitted by the tsetse fly continues to be a public health issue, despite more than a century of research. There are two types of the disease, the chronic gambiense and the acute rhodesiense-HAT. Fly abundance and distribution have been affected by changes in land-use patterns and climate. However, disease transmission still continues. Here, we review some aspects of HAT ecoepidemiology in the context of altered infestation patterns and maintenance of the transmission cycle as well as emerging options in disease and vector control.

Identification of Glossina palpalis gambiensis specific salivary antigens: towards the development of a serologic biomarker of human exposure to tsetse flies in West Africa.

The saliva of blood sucking arthropods contains a number of pharmacologically active compounds that induce an antibody response in exposed human individuals. The objectives of the present study were (i) to assess the human IgG response directed against salivary antigens of Glossina palpalis gambiensis, the main vector of Trypanosoma brucei gambiense in West Africa, as a biomarker of human-tsetse contacts; and (ii) to identify specific salivary antigens. Immune reactivity of human plasma collected within active human African trypanosomiasis (HAT) foci (coastal Guinea), historical foci where tsetse flies are still present (South-West Burkina Faso) and a tsetse free area (Bobo-Dioulasso, Burkina Faso), was measured by ELISA against whole saliva extracts. In the active HAT foci and areas where tsetse flies were present in high densities, specific IgG responses were significantly higher (p < 0.0001) to those in Bobo-Dioulasso or in Loropeni, where tsetse flies were either absent or only present at low densities. Furthermore, 2D-electrophoresis combined with mass spectrometry enabled to reveal that several antigens were specifically recognized by plasma from exposed individuals. Among them, four salivary proteins were successfully identified (Ada, 5'Nuc, Ag5 and Tsgf1). These results represent a first attempt to identify Glossina salivary proteins or synthetic peptides to develop a standardized and specific biomarker of tsetse exposure in West Africa.

The antiviral drug valacyclovir successfully suppresses salivary gland hypertrophy virus (SGHV) in laboratory colonies of Glossina pallidipes.

Many species of tsetse flies are infected with a virus that causes salivary gland hypertrophy (SGH) symptoms associated with a reduced fecundity and fertility. A high prevalence of SGH has been correlated with the collapse of two laboratory colonies of Glossina pallidipes and colony maintenance problems in a mass rearing facility in Ethiopia. Mass-production of G. pallidipes is crucial for programs of tsetse control including the sterile insect technique (SIT), and therefore requires a management strategy for this virus. Based on the homology of DNA polymerase between salivary gland hypertrophy virus and herpes viruses at the amino acid level, two antiviral drugs, valacyclovir and acyclovir, classically used against herpes viruses were selected and tested for their toxicity on tsetse flies and their impact on virus replication. While long term per os administration of acyclovir resulted in a significant reduction of productivity of the colonies, no negative effect was observed in colonies fed with valacyclovir-treated blood. Furthermore, treatment of a tsetse colony with valacyclovir for 83 weeks resulted in a significant reduction of viral loads and consequently suppression of SGH symptoms. The combination of initial selection of SGHV-negative flies by non-destructive PCR, a clean feeding system, and valacyclovir treatment resulted in a colony that was free of SGH syndromes in 33 weeks. This is the first report of the use of a drug to control a viral infection in an insect and of the demonstration that valacyclovir can be used to suppress SGH in colonies of G. pallidipes.

The prevalence of African animal trypanosomoses and tsetse presence in Western Senegal.

In 2005, the Government of Senegal initiated a tsetse eradication campaign in the Niayes and La Petite Côte aiming at the removal of African Animal Trypanosomosis (AAT), which is one of the main constraints to the development of more effective cattle production systems. The target area has particular meteorological and ecological characteristics that provide great potential for animal production, but it is unfortunately still infested by the riverine tsetse species Glossina palpalis gambiensis Vanderplank (Diptera: Glossinidae). The tsetse project in Senegal has adopted an area-wide integrated pest management (AW-IPM) approach that targets the entire tsetse population within a delimited area. During the first phase of the programme, a feasibility study was conducted that included the collection of entomological, veterinary, population genetics, environmental and socioeconomic baseline data. This paper presents the parasitological and serological prevalence data of AAT in cattle residing inside and outside the tsetse-infested areas of the target zone prior to the control effort. At the herd level, a mean parasitological prevalence of 2.4% was observed, whereas a serological prevalence of 28.7%, 4.4%, and 0.3% was obtained for Trypanosoma vivax, T. congolense and T. brucei brucei, respectively. The observed infection risk was 3 times higher for T. congolense and T. vivax in the tsetse-infested than in the assumed tsetse-free areas. Moreover, AAT prevalence decreased significantly with distance from the nearest tsetse captured which indicated that cyclical transmission of the parasites by tsetse was predominant over mechanical transmission by numerous other biting flies present. The importance of these results for the development of a control strategy for the planned AW-IPM campaign is discussed.

Serratia glossinae sp. nov., isolated from the midgut of the tsetse fly Glossina palpalis gambiensis.

We report the isolation of a novel bacterium, strain C1(T), from the midgut of the tsetse fly Glossina palpalis gambiensis, one of the vector insects responsible for transmission of the trypanosomes that cause sleeping sickness in sub-Saharan African countries. Strain C1(T) is a motile, facultatively anaerobic, rod-like bacterium (0.8-1.0 microm in diameter; 2-6 microm long) that grows as single cells or in chains. Optimum growth occurred at 25-35 degrees C, at pH 6.7-8.4 and in medium containing 5-20 g NaCl l(-1). The bacterium hydrolysed urea and used L-lysine, L-ornithine, citrate, pyruvate, D-glucose, D-mannitol, inositol, D-sorbitol, melibiose, amygdalin, L-arabinose, arbutin, aesculin, D-fructose, D-galactose, glycerol, maltose, D-mannose, raffinose, trehalose and d-xylose; it produced acetoin, reduced nitrate to nitrite and was positive for beta-galactosidase and catalase. The DNA G+C content was 53.6 mol%. It was related phylogenetically to members of the genus Serratia, family Enterobacteriaceae, the type strain of Serratia fonticola being its closest relative (99 % similarity between 16S rRNA gene sequences). However, DNA-DNA relatedness between strain C1(T) and S. fonticola DSM 4576(T) was only 37.15 %. Therefore, on the basis of morphological, nutritional, physiological and fatty acid analysis and genetic criteria, strain C1(T) is proposed to be assigned to a novel Serratia species, Serratia glossinae sp. nov. (type strain C1(T) =DSM 22080(T) =CCUG 57457(T)).

Knowledge, attitudes and practices on tsetse and sleeping sickness among communities living in and around Serengeti National Park, Tanzania.

A study was undertaken to investigate knowledge, attitudes and practices about sleeping sickness (human African trypanosomiasis) among communities living in and around Serengeti National Park (SENAPA). Structured questionnaires were administered to a total of 1490 consenting participants. Of the respondents, 924 (62%) knew sleeping sickness, and 807 (87.3%) knew the right place to seek healthcare. Of 924 who knew sleeping sickness, 386 (42%) said the disease was present in the areas they live. Most respondents (85.4%) knew that sleeping sickness infections were acquired in the bush and forest. The most common (69.3%) sources of information about sleeping sickness were relatives and friends. Symptoms of sleeping sickness mentioned included abnormal sleep (45.2%), fever (35.3%), body malaise (14.5%), headache (7.6%) and lymph node enlargement (6.1%). Of 1490 people interviewed 90.4% knew tsetse flies and 89.8% had been bitten by tsetse flies. The majority (86.6%) of the respondents knew that sleeping sickness is transmitted through a tsetse bite. Activities that exposed people to tsetse bites included working in tsetse infested bushes/forests, grazing livestock in tsetse infested areas and hunting game animals. In conclusion, communities living in and around SENAPA were knowledgeable about tsetse and sleeping sickness. The communities can thus understand and support community based tsetse and sleeping sickness control programmes to ensure success.

Inactivation and reactivation of a variant-specific antigen gene in cyclically transmitted Trypanosoma brucei.

In Trypanosoma brucei, the activation of the variant-specific antigen gene AnTat 1.1 proceeds by the synthesis of an additional gene copy, the AnTat 1.1 ELC, which is transposed to a new location, the expression site, where it is transcribed. Using the AnTat 1.1 variant to infect flies, we investigated the fate of the AnTat 1.1 ELC during cyclic transmission of T. brucei. We show here that the AnTat 1.1 ELC is conserved in procyclic trypanosomes, obtained either from the midgut of infected Glossina or from cultures, and in metacyclic trypanosomes, although the AnTat 1.1 serotype is not detected among metacyclic antigen types. This same AnTat 1.1 ELC, which is thus silent as the parasite develops in the insect vector, can be reactivated without duplication during the first parasitemia wave following cyclical transmission. This re-expression of the conserved ELC accounts for the early appearance of the 'ingested' antigenic type after passage through the fly.