Abstract
Tsetse-transmitted trypanosomiases are among the most neglected tropical diseases in sub-Sahara Africa. Although all tsetse species are susceptible to trypanosome infections, their differential attraction/feeding preferences for different wildlife, domestic animals, and/or humans constitute critical determinants of trypanosomes species they predominantly transmit. Artificial bait technologies, based on long-range tsetse olfactory responses to natural cues emitted by preferred hosts and blends of synthetic versions that mimic these cues, have successfully been applied in attractant-odor-based (“pull” tactic) reduction of field populations of some tsetse species. Olfactory attribute associated with active avoidance of tsetse-refractory non-hosts has similarly been exploited in design of repellent-odor-based (“push” tactic) protection of livestock. These tactics have opened possibility of spatially strategic deployment of the two sets of odor baits in “push-pull” tactics. Possibility of developing blends with enhanced attraction and repellence compared with those associated with savannah tsetse fly hosts and non-hosts, respectively, have been explored, where structure activity and blends of different components generated two novel blends. The studies evaluated structure activity and blends of different components. One based on attractive constituents associated with buffalo (Syncerus caffer) comprised of ε-nonalactone, nonanoic acid, 2-nonanone (in 1:3:2 proportion) delivered together with acetone, which showed significantly better attractancy on savannah tsetse fly than the standard blend comprised of 3-propylphenol, octenol, p-cresol, and acetone (POCA). The other blend comprised of δ-nonalactone, heptanoic acid, 4-methylguaiacol and geranylacetone (in 6:4:2:1 proportion) was significantly more repellent than previously characterized blend based on tsetse fly refractory waterbuck (Kobus defassa) constituents (δ-octalactone, pentanoic acid, guaiacol and geranylacetone). So far, no effective attractants or repellents of riverine tsetse fly species have been characterized. Optimized attractant and repellent blends for savannah tsetse flies lay down useful groundwork for future development of the “push-pull” deployment tactic for area-wide control of tsetse flies. Better understanding of the physiological, cellular, and molecular basis of response in the tsetse fly to odors can potentially augment the current tsetse fly-control interventions.
Highlights
Different groups of tsetse fly species are distributed in almost all of sub-Sahara Africa and transmit Human African Trypanosomiasis (HAT) and Animal African Trypanosomiasis (AAT) causative trypanosomes (Simarro et al, 2010; Cecchi et al, 2015), infesting ten million-square kilometers in 36 countries
Duration of apparent reluctance to accept and expand the role of insecticides was later experienced since insecticides appeared to provide only a temporary solution to a permanent problem, manifested by tsetse fly re-infestation of cleared areas due to temporal degradation of insecticide toxicity, among other factors (Allsopp, 1984)
The live animal bait technologies for tsetse fly control were demonstrated in southern Africa in the mid-1980s, but seemed of limited use where the intention was to remove tsetse flies from the vast invasion source or where cattle were absent or could not be introduced (Colvin and Gibson, 1992; Vreysen et al, 2013)
Summary
Different groups of tsetse fly species are distributed in almost all of sub-Sahara Africa and transmit Human African Trypanosomiasis (HAT) and Animal African Trypanosomiasis (AAT) causative trypanosomes (Simarro et al, 2010; Cecchi et al, 2015), infesting ten million-square kilometers in 36 countries. The Morsitans group consists of five species of which Glossina morsitans morsitans, Glossina pallidipes, Glossina swynnertoni and Glossina longipalpis (Colvin and Gibson, 1992) are restricted to the savannah, while Glossina austeni occupy coastal forests. Mammalian vaccines against HAT are still in their early stages of discovery due to the complex mechanism of antigenic variations associated with the trypanosome parasite (Onyilagha and Uzonna, 2019; Autheman et al, 2021)
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