Efficacy of fabric panels impregnated with metarhizium anisopliae against adult glossina fuscipes fuscipes in Manga and Magare islands, lake Victoria, Kenya
Riithi, Naomi Nyambura
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Tsetse flies (Glossina sp.) transmit parasites of the genus Trypanosoma that cause Human African Trypanosomiasis (sleeping sickness) in man and Animal African trypanosomiasis in livestock and wildlife. African Trypanosomiasis is a devastating tropical disease that is endemic to 38 countries in sub-Saharan Africa. Integrated management of tsetse flies using pyrethroid insecticides has been the mainstay of trypanosomiasis control. Vector control and disease treatment have led to drastic declines in the incidence of sleeping sickness, hence, the World Health Organization set a goal to eliminate the disease by 2030. Despite this progress, African trypanosomiasis still impacts substantial health and economic burden in less fortunate communities in Sub-Saharan Africa. There is, therefore, a need for supplementary vector control strategies which are cost-effective and easy to maintain to fight this disease. The entomopathogen Metarhizium anisopliae has been effective in reducing tsetse flies longevity and overall vectorial capacity, while being cost-effective and easy to deploy. This study evaluated the efficacy of fabric panels impregnated with M. anisopliae against adults of Glossina fuscipes fuscipes in Manga and Magare islands of Lake Victoria in Kenya. Baseline studies were conducted to determine the existence of natural M. anisopliae using molecular analysis tools. For eight days, between 9.00 - 12.00 h, tsetse flies were sampled with four biconical traps and four targets with adhesives set 1m from the lakeshore at intervals of 200 m. Tsetse flies trapped were screened for naturally occurring M. anisopliae DNA. To compare the capacity of polyester, cotton and fleece fabrics to retain fungal conidia, panels were made by sewing 25 cm × 25 cm of each on pthalogen blue cotton fabric. Three replicates of each panel were treated with 0.1 g/cm2 of conidia and suspended 10 cm from the ground for fifteen days. Every 24 hours, conidia were sampled on three random points of each fabric and quantified. Electrocuting nets were used to estimate the attraction and landing rate of tsetse flies on panels with conidia doses of 0.25 – 1.00 g. The effectiveness of the fabric panels to disseminate lethal dosages of M. anisopliae to tsetse flies were evaluated by setting five panels treated with conidia dosage of 0.25 g in Manga Island. Five untreated panels in Magare island served as control. Tsetse flies were collected using biconical traps on each island and maintained on rabbit blood in the tsetse fly insectary. Dead flies were placed on petri dishes with dump paper towels and observed for mycosis after 5 days. Counts of tsetse flies and conidia were analysed in R packages using the zero-inflated generalised linear models and mortality rates estimated with Kaplan-Meier models. A total of 2,415 Glossina fuscipes fuscipes were trapped with 3.7 times (95 % Confidence Interval (CI) 2.8 - 4.9 flies, p>0.01) more tsetse flies were trapped in Manga Island than Magare island. There was zero detection of naturally occurring M. anisopliae DNA in the trapped tsetse flies. Fleece fabrics retained seven times (95 % CI: 5.6 - 8.8 times, p<0.01) more conidia than polyester and 1.2 times (95 % CI: 1.0 – 1.5 times, p=0.04) more than cotton fabrics. Incorporation of 1 g of conidia to panels reduced the landing rate of tsetse flies by 60 % (95 % CI: 30 – 70 %, p<0.01). Significantly fewer tsetse flies attempted to land on panels with conidia doses of 0.5 g and 1.0 g (p<0.05). Female tsetse flies were more affected by the colour change on the treated fabric panels. The prevalence of M. anisopliae on tsetse flies increased steadily to 24 % and 16.7 % in Manga and Magare islands respectively over three weeks. This study demonstrates that fabric panels made from fleece fabric and treated with 0.25 g of M. anisopliae conidia can effectively contaminate G. f. fuscipes in the field with the entomopathogen. With further optimization, the prototype can be developed into an effective large scale vector control tool.
- MST-Zoological Sciences