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The Sterile Insect Technique (SIT)
The SIT exploits the particular mating biology of tsetse, whereby female flies rarely mate more than once. Male flies are therefore mass reared in the laboratory, sterilized by irradiation, and released to mate with wild females. Females mated with sterile males are unable to produce offspring. Unlike all other tsetse control techniques, SIT has no effect on non-target organisms. Also unlike other techniques, SIT becomes more efficient at lower fly densities, and is ideally suited to the final phase of local tsetse eradication (F.A.S. Kuzoe and C.J. Schofield, 2004). Sterile Insect Technique (SIT) involves mass rearing of target insects in a laboratory and sterilizing the males by exposing them to low doses of radiation. These sterile male flies are then released by air over infested areas, where they mate with wild females. If the sterile males vastly outnumber the fertile wild males, the wild fly population quickly dies out. The proportion of infertile males to fertile wild males must be at least 10:1. The most notable success of SIT against tsetse was in eradicating G. austeni Newstead on Unguja Island; Zanzibar with 50:1 infertile to fertile male proportion (Hargrove, 2003). The SIT is an area-wide method used to “mop up” residual tsetse populations when conventional techniques succeed in reducing populations to extremely low levels (Vreysen, et al., 2013). Currently in Ghana, the SIT is considered a future option when tsetse populations have been reduced to significantly low levels.
A Continental Approach to Tsetse Control/Eradication
African Heads of State and Government, having been under pressure from their communities to do something about the tsetse fly, and realizing that individual country solutions would not work, came to the conclusion that the tsetse problem was trans-boundary in nature and had to be tackled on a continent-wide basis (AU Commission Action Plan 2001). In an effort to have greater impact on tsetse control efforts and for better utilization of resources, African Heads of State and governments in Lome 2000 passed a declaration that essentially called for a concerted effort between countries in the fight against tsetse flies. The signing of the protocol saw the establishment of the Pan-African Tsetse and Trypanosomiasis Eradication Campaign (PATTEC). Under the PATTEC initiative, Ghana, Burkina Faso and Mali in the West African sub-region initiated a project to create tsetse free areas across their common borders. A similar common border initiative was established between Kenya, Uganda and Ethiopia in the East African sub-region.
Distribution of Glossina species in the study area
A total of 3561 tsetse flies were caught (Table 1). Flies caught on the first day of the survey (482 flies) were lost before their sex and species could be determined. The tsetse survey revealed the presence of two Glossina species i.e. G. tachinoides and G. palpalis gambiensis. G. tachinoides was caught adjacent to the three main rivers of the Upper West Region, and thus appears to be distributed throughout the study area (Fig. 1). The highest values of apparent abundance were found in the South-western tip of the Upper West.
Region, along the Black Volta River (IAA > 100). By contrast, G. palpalis gambiensis was absent from most of the study area, and flies of this species were only found at its extreme South, along the Kulpawn and Black Volta River basins (Fig. 1). The mean IAA of tsetse was 8.7, 1.9 and 1.2 for samples taken along the Black Volta, Kulpawn and Sissili Rivers, respectively.
P revalence of bovine trypanosomosis based on serological and parasitological examin ation
The parasitological and sero logical prevalence of bovine trypanosomosis in eac h of the grids of the Upper West R egion are presented in Table 2 and Fig. 2. Trypanosomal infections were detected in cattle from 18 of the 36 selected grids. The average parasitological pre valence was 2.5% (95% CI: 1.1–5.8). Only infections with T. vivax (27) and T. brucei (7) were detected parasitologically. The parasitological prevalence of trypanosomal infections was highest in the Sanga breed. Anti-trypanosomal antibodies were detected in cattle sampled in 29 of the 36 grids (Fig. 2). In all grids, the serological prevalence of trypanosomal infections was substantially higher compared to the parasitological prevalence. The average prevalence of anti-trypanosomal antibodies was 19% (95% CI: 14–25). The prevalence of anti-trypanosomal antibodies was highest in adult animals of the Zebu breed (Fig. 3). The average PCV of the WASH, the Sanga and Zebu cattle was 30%, 31% and 32%, respectively (Table 2). The PCV did not differ significantly between parasitologically positive and negative animals (p = 0.4 in stepwise backward selection of estimators). Little variations were observed between PCV values in seropositive and seronegative animals of the WASH and Zebu breeds (Fig. 3). In Sanga breed cattle, on the other hand, the average P CV of seropositive animals was lower (p = 0.01 in females and 0.1 in males; Fig. 3).
Locus selection
Traps closer than 300 m (sub-groups, as defined for the HierFstat analysis in the Material and Methods section) were used as population units in order to optimize both subsample sizes and subsample numbers. The locus by locus analysis (Supplementary material 1-2) indicated that locus pGp17 displayed an FIS of almost 1 that was significantly different from the mean. Locus pGp29 displayed an unusually small FIS and FST that appeared significantly different from the mean over all loci and could be reflecting some kind of selection signature. Both loci were therefore removed from the data for further analyses that was carried out with the remaining seven loci (XB104, XpGp13, XpGp20, C102, GpCAG133, pGp24 and pGp28).
Hierarchical population structure
The significance of the different hierarchical levels was tested with HierFstat. This analysis indicated a non-significant effect of sub-groups within sites (FSG-S <0, P-value=1). When this level was ignored, we obtained a non-significant effect of locations within river basins (FL-RB <0, P-value=0.166). The non significant effect of a hierarchical effect simply means no supplementary information is brought by this level. It does not mean that no genetic differentiation occurs between individuals belonging to different units of this hierarchy (see supplementary material of (Rougeron et al., 2009) for a detailed explanation). The remaining levels appeared to significantly affect genetic diversity distribution: traps within subgroups (FTr-SG=0.038, P-value=0.043), sites within river basins (FS-RB=0.047, P-value=0.001) and river basins within the total (FRB-T=0.056, P-value=0.037). The level “Trap” displayed the weakest effect, though significant, which is not typical for G. tachinoides that usually differentiates genetically at higher scales ( Koné et al., 2011 and Koné et al., 2010). In further analysis we tested and measured local parameters (linkage disequilibrium and FIS) within traps and within sites.
Local population structure
Within traps, one pair of loci significantly displayed a linkage disequilibrium (P-value=0.007) and within subgroups and within sites, one pair of loci also showed significant linkage (P-value<0.03). This is not significantly above the 5% expected under the null hypothesis (unilateral exact binomial test, P-value=0.6594 for 21 tests with 7 loci) and became not significant after Bonferroni correction. We can therefore assume no or very weak statistical association between the seven microsatellite loci.
Across loci there was a significant and highly variable heterozygote deficit within traps as illustrated in Fig. 2. Only two loci displayed heterozygote excess (FIS=-0.066 for XpGp13 and FIS=-0.08 for GpCAG133) as expected in a dioecious species. Null alleles were probably responsible for the observed pattern. MicroChecker analyses confirmed that all heterozygote deficits can largely be explained by null alleles (smallest P-value>0.13, Table 2).
Table of contents :
General Introduction
Chapter 1 Bovine Trypanosomosis (Disease) & Vector control : A General review
1.1. Introduction
1.2. Epidemiology and Risk factors of Trypanosomosis
1.2.1. Patterns of trypanosomosis on the field
1.2.2. Vector-Parasite-Host Relationship
1.2.3. Risk factors of Trypanosomosis
1.2.4. Trypanosomosis as a Trans-boundary Animal Disease
1.3. Tsetse and Trypanosomosis Control
1.3.1. Considerations for Tsetse Control Programmes
1.3.1.1. Socio-economic Baseline Survey
1.3.1.2. Entomological and disease Baseline Survey
1.3.1.3. Tsetse population structuring (Population Genetic profiling)
1.3.2. Control of parasitic Trypanosomes
1.3.3. Entomological (Vector) Control Strategy
1.3.3.1. Environmental management as a vector control strategy
1.3.3.2. Pesticide campaign in Vector Control
1.3.3.2.1. Live bait technique
1.3.3.2.2. Ground spraying
1.3.3.2.3. Aerial Spraying: The Sequential Aerosol Technique (SAT)
1.3.3.2.4. Traps and Targets
1.3.3.3 The Sterile Insect Technique (SIT)
1.4. A Continental Approach to Tsetse Control/Eradication….
1.5. References
Chapter 2 : Cross-sectional survey
Bovine trypanosomosis in the Upper West Region of Ghana: Entomological, parasitological and serological cross-sectional surveys
Abstract
2.1. Introduction
2.2. Materials and methods
2.2.1. Study area
2.2.2. Entomological surveys
2.2.3. Parasitological and serological survey of bovine trypanosomosis
2.2.3.1. Sampling framework
2.2.3.2. Sampling and processing
2.2.3.3. Serological diagnosis
2.2.4. Statistical analysis
2.3. Results
2.3.1. Distribution of Glossina species in the study area
2.3.2. Prevalence of bovine trypanosomosis based on serological and parasitological examination
2.4. Discussion
2.5. Conclusion
2.6. References
Chapter 3: Tsetse population genetics
Genetic Comparison of Glossina tachinoides Populations in Three River Basins of the Upper West Region of Ghana and Implications for Tsetse Control
Abstract
3.1. Introduction
3.2. Materials and Methods
3.2.1. Study area and location of the genotyped flies
3.2.2. Entomological sampling
3.2.3. Genotyping
3.2.4 Statistical analyses
3.3. Results
3.3.1 Locus selection
3.3.2. Hierarchical population structure
3.3.3. Local population structure
3.3.4. Sex biased dispersal
3.3.5. Isolation by distance and demographic inferences
3.4. Discussion
3.5. References
Chapter 4: Integrated Tsetse Control
Sequential Aerosol Technique: A Major Component in an Integrated Strategy of Intervention against Riverine Tsetse in Ghana
Abstract
4.1. Introduction
4.2. Materials and Methods
4.2.1. Study area and sequential aerosol technique
4.2.2. Other control techniques
4.2.3. Monitoring the impact of the control campaign
4.3. Results
4.3.1. SAT schedule
4.3.2. Efficacy of the SAT cycles
4.3.3. Efficacy of the integrated tsetse control campaign
4.4. Discussion
4.5. References
Chapter 5 : Sellection of monitoring sites
Considerations for the Selection of Monitoring Sites in a post SAT Tsetse Control Programme
Chapter 6 : Environmental impact assessment
Environmental impact assessment of Deltamethrin application
Chapter 7 General Discussion/Conclusion
7.1. Introduction
7.2. Vector and Trypanosomosis (Disease) surveys
7.3. Study of G. tachinoides population structuring in the UWR of Ghana..
7.4. Integrated application of SAT and other complementary control methods
7.5. Impacts of Deltamethrin Aerosol application for tsetse suppression on aquatic and terrestrial invertebrates in the Upper West Region of Ghana.
7.6. The integrated Control Strategy
7.7. Conclusion
7.8. Reference:
