Prevalence of pathogenic trypanosomes in anaemic cattle from trypanosomosis challenged areas of Itezhi-tezhi district in central Zambia

BACKGROUND : The measure of anaemia status using packed cell volume (PCV) can be a reliable indicator of African trypanosomosis (AT) in the absence of other anaemia-causing conditions. However, studies that have estimated prevalence of anaemia in cattle from AT endemic areas have rarely reported the prevalence of the disease in the anaemic cattle. Therefore we investigated the prevalence of AT in anaemic cattle at sites that had recently reported the disease in Itezhi tezhi district of central Zambia. METHODS : During a survey, blood samples were collected from 564 randomly selected cattle for anaemia determination from seven crush pens (Mutenda, Kapulwe, Banachoongo, Itumbi, Iyanda, New Ngoma and Shinampamba). At a PCV- value cut off of 26 %, all samples positive for anaemia were subjected to both parasitological examination on thick and thin blood smears and polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) for detection of trypanosome DNA. Fisher’s exact test and a mixed effect logistic regression analyses were used to determine and measures associations, respectively. RESULTS : Of 564 cattle screened, 58 (10.3 %; 95 % CI: 7.8–12.8 %) had anaemia. PCR-RFLP results showed that 17 (29.3 %; 95 % CI; 17.2–41.4 %) anaemic cattle were positive for pathogenic trypanosomes compared to 1 (1.7 %; 95 % CI: 0.0–5.2 %) on parasitological examination using thick smears. The infections were caused by Trypanosoma congolense and Trypanosoma vivax. Fisher’s exact test showed a strong association between PCV and pathogenic trypanosome infection (P = 0.004). A mixed effect multivariate logistic regression showed that a one unit increase in PCV reduced the likelihood of detecting AT with PCR-RFLP by 24.7 % (95 % CI: 4.6–40.6 %; P = 0.019) in anaemic cattle, taking into account their age and sex, with random effects for crush pen. CONCLUSION : These results suggest that T. congolense and T. vivax could be important causes of anaemia in cattle reared in AT endemic areas of Itezhi tezhi in Central Zambia. This also suggests that even though pathogenic trypanosomal infection was strongly associated with PCV, it could only account for up to 41 % of the anaemia in cattle. Therefore further investigation to ascertain other factors responsible for anaemia in AT endemic areas of Itezhi tezhi in Central Zambia is needed.Norad's Programme for Master Studies (NOMA, ref No. 2010/12841) and the Norwegian Agency for Development Cooperation (Norad) through SIU.http://www.parasitesandvectors.comam201

A novel vehicle-mounted sticky trap ; an effective sampling tool for savannah tsetse flies Glossina morsitans morsitans Westwood and Glossina morsitans centralis Machado

BACKGROUND: Black screen fly round (BFR) is a mobile sampling method for Glossina morsitans. This technique relies on the ability of operator(s) to capture flies landing on the screen with hand nets. In this study, we aimed to evaluate a vehicle-mounted sticky panel trap (VST) that is independent of the operator’s ability to capture flies against BFR, for effective and rapid sampling of G. m. morsitans Westwood and G. m. centralis Machado. We also determined the influence of the VST colour (all-blue, all-black or 1:1 blue-black), orientation and presence of odour attractants on tsetse catch. METHODOLOGY/PRINCIPAL FINDINGS: Using randomised block design experiments conducted in Zambia, we compared and modelled the number of tsetse flies caught in the treatment arms using negative binomial regression. There were no significant differences in the catch indices of the three colour designs and for in-line or transversely oriented panels for both subspecies (P > 0.05). When baited with butanone and 1-octen-3-ol, VST caught 1.38 (1.11–1.72; P < 0.01) times more G. m. centralis flies than the un-baited trap. Attractants did not significantly increase the VST catch index for G. m. morsitans (P > 0.05). Overall, the VST caught 2.42 (1.91–3.10; P < 0.001) and 2.60 (1.50–3.21; P < 0.001) times more G. m. centralis and G. m. morsitans respectively, than the BFR. The VST and BFR took 10 and 35 min respectively to cover a 1 km transect. CONCLUSIONS/SIGNIFICANCE: The VST is several times more effective for sampling G. m. morsitans and G. m. centralis than the BFR and we recommend its use as an alternative sampling tool.https://journals.plos.org/plosntdspm2022Zoology and Entomolog

A novel vehicle-mounted sticky trap; an effective sampling tool for savannah tsetse flies Glossina morsitans morsitans Westwood and Glossina morsitans centralis Machado.

BACKGROUND: Black screen fly round (BFR) is a mobile sampling method for Glossina morsitans. This technique relies on the ability of operator(s) to capture flies landing on the screen with hand nets. In this study, we aimed to evaluate a vehicle-mounted sticky panel trap (VST) that is independent of the operator's ability to capture flies against BFR, for effective and rapid sampling of G. m. morsitans Westwood and G. m. centralis Machado. We also determined the influence of the VST colour (all-blue, all-black or 1:1 blue-black), orientation and presence of odour attractants on tsetse catch. METHODOLOGY/PRINCIPAL FINDINGS: Using randomised block design experiments conducted in Zambia, we compared and modelled the number of tsetse flies caught in the treatment arms using negative binomial regression. There were no significant differences in the catch indices of the three colour designs and for in-line or transversely oriented panels for both subspecies (P > 0.05). When baited with butanone and 1-octen-3-ol, VST caught 1.38 (1.11-1.72; P 0.05). Overall, the VST caught 2.42 (1.91-3.10; P < 0.001) and 2.60 (1.50-3.21; P < 0.001) times more G. m. centralis and G. m. morsitans respectively, than the BFR. The VST and BFR took 10 and 35 min respectively to cover a 1 km transect. CONCLUSION/SIGNIFICANCE: The VST is several times more effective for sampling G. m. morsitans and G. m. centralis than the BFR and we recommend its use as an alternative sampling tool

Efficacy of bednets with dual insecticide-treated netting (Interceptor® G2) on side and roof panels against Anopheles arabiensis in north-eastern Tanzania.

BACKGROUND: Optimising insecticide use and managing insecticide resistance are important to sustain gains against malaria using long-lasting insecticidal nets (LLINs). Restricting insecticides to where mosquitoes are most likely to make multiple contacts could reduce the quantity of insecticide needed to treat the nets. Previous studies have shown that nets partially treated with a pyrethroid insecticide had equivalent mortality compared to a fully treated net. This study compared the efficacy of: (i) whole Interceptor® G2 nets (IG2; a dual-active LLIN containing alpha-cypermethrin and chlorfenapyr), (ii) nets with roof panels made of IG2 netting, (iii) nets with side panels made of IG2 netting and (iv) whole untreated nets as test nets. METHODS: The study was conducted in cow-baited experimental huts, Moshi Tanzania, using a four-arm Latin square design. Test nets had 30 holes cut in panels to simulate a typical net after 2-3 year use. The trial data were analysed using generalized linear models with mortality, blood-feeding, exophily and deterrence against wild free-flying Anopheles arabiensis as outcomes and test nets as predictors. RESULTS: Mortality was significantly higher in the nets with roof IG2 [27%, P = 0.001, odds ratio (OR) = 51.0, 95% CI = 4.8-546.2), side IG2 (44%, P < 0.001, OR = 137.6, 95% CI = 12.2-1553.2] and whole IG2 (53%, P < 0.001, OR = 223.0, 95% CI = 19.07-2606.0) nettings than the untreated (1%) nets. Mortality was also significantly higher in the whole IG2 net compared to the net with roof IG2 netting (P = 0.009, OR = 4.4, 95% CI = 1.4-13.3). Blood feeding was 22% in untreated, 10% in roof IG2, 14% in side IG2 and 19% in whole IG2 nets. Exiting was 92% in untreated, 89% in roof IG2, 97% in side IG2 and 94% whole IG2 nets. CONCLUSION: The results show that although the roof-treated IG2 net induced greater mortality compared to untreated nets, its efficacy was reduced compared to whole IG2 nets. Therefore, there was no benefit to be gained from restricting dual-active ingredient IG2 netting to the roof of nets

A non-inferiority and GLP-compliant study of broflanilide IRS (VECTRON™ T500), a novel meta-diamide insecticide against Anopheles arabiensis

Management of insecticide resistance in vector control requires development and evaluation of active ingredients (AIs) with new modes of action. VECTRON™ T500 is a wettable powder formulation used for Indoor Residual Spraying (IRS) containing 50% of broflanilide as an AI. This study evaluated the efficacy of VECTRON™ T500 sprayed on blocks of different substrates (concrete, mud and plywood) against pyrethroid susceptible and resistant Anopheles gambiae sensu stricto (s.s.) strains, and wild An. arabiensis. It also assessed the efficacy of VECTRON™ T500 in experimental huts plastered with mud and concrete against wild free-flying An. arabiensis; and non-inferiority to a World Health Organization listed indoor residual spraying product Actellic® 300CS in terms of mortality in Moshi, Tanzania.Monthly cone bioassays on blocks and in experimental huts (against pyrethroid susceptible and resistant An. gambiae s.s.) were conducted over a 12-month period after spraying of VECTRON™ T500 and Actellic® CS300. Collections of wild free-flying An. arabiensis were also done in the sprayed huts. The main outcome for cone bioassays was mortality while for the wild hut trial collections, it was mortality and blood feeding inhibition. Grouped logistic regressions with random effects were used to analyse all dichotomous outcome variables from wild collections.The results showed residual efficacy of VECTRON™ T500 of at least 80% mortality was longest on concrete, followed by plywood and then mud substrates for all mosquito strains. Furthermore, VECTRON™ T500 significantly increased the likelihood of mortality (OR:> 1.37, P<0.001) in wild collections of An. arabiensis compared to Actellic® 300CS. Blood feeding was not significantly different in the wild collection of An. arabiensis between VECTRON™ T500 and Actellic® 300CS arms.These results show that VECTRON™ T500 is efficacious against pyrethroid-resistant An. gambiae s.s. and non-inferior to Actellic® 300CS. Therefore, it should be an important addition to the current arsenal of insecticides used for insecticide resistance management and vector control

Wing length of tsetse caught by stationary and mobile sampling methods

INTRODUCTION : A variety of techniques have been used to control tsetse with varying degrees of success. In a study on the population structure of Glossina fuscipes fuscipes that recovered after a previous vector control trial on two Kenyan islands, it was reported that the average fly size on the intervention islands was significantly smaller than on the none intervention islands and also compared to the size before the intervention. The conclusion was that vector control using tiny targets exerted size selection pressure on the population. The study recommended for further studies and suggested that this phenomenon could be among the reasons why targets used as a sole control method have rare reports of successful elimination of tsetse populations. Therefore, in this paper we report on a study of body size of tsetse flies caught in epsilon traps (as a stationary device) and black screen fly rounds (as a mobile trapping device). MATERIALS AND METHODS : The study was carried out in eastern Zambia to test the hypothesis that the body size (measured as wing length) of G. m. morsitans males or females, captured by epsilon traps and fly rounds is the same. RESULTS : A total of 1442 (489 females and 953 males) wing length measurements of G. m. morsitans were used in the analysis. It was established that tsetse flies caught by epsilon traps are on average larger than those caught by fly rounds. The likelihood of a large female or male fly being caught by traps, relative to a small one, significantly increased by 5.088 times (95% CI: 3.138–8.429) and by 2.563 times (95% CI: 1.584–4.148), respectively, p < 0.0001, compared with being caught by fly rounds. The hypothesis was rejected. CONCLUSION : This study showed that epsilon traps capture significantly larger G. m. morsitans than fly rounds do. Therefore, further research is recommended to verify i) whether the predilection of traps to capture larger flies has an effect on the process of tsetse elimination when targets are used e.g. targets may take longer to reach elimination than if the predilection was not there, ii) whether different results can be obtained on ecogeographic distribution of different sizes of the species if fly rounds are used for sampling instead of epsilon traps. The results from such studies could influence the strategies used in future control operations.Data for: Wing length of tsetse caught by stationary and mobile sampling methods The disease of interest is trypanosomiasis that is transmitted by tsetse flies (Glossina sp). The disease affects both human and livestock. (https://data.mendeley.com/datasets/jpx5brm3bp/1)The Wellcome Trusthttp://www.elsevier.com/locate/actatropica2021-04-01hj2020Veterinary Tropical Disease

Efficiencies of stationary sampling tools for the tsetse fly Glossina fuscipes fuscipes in western Kenya

Monitoring the effectiveness of tsetse fly control interventions that aim to reduce transmission of African trypanosomiasis requires highly efficient sampling tools that can catch flies at low densities. The sticky small target (StS-target) has previously been shown to be more effective in sampling Glossina fuscipes fuscipes compared to the biconical trap. However, its efficiency in terms of the proportion of flies it catches out of those that visit it has not been reported. Furthermore, there are no reports on whether tsetse samples caught using the StS-target can be used for subsequent processes such as molecular tests. In this study, we evaluated the efficiency of the biconical trap and targets for sampling G. f. fuscipes. All targets were tiny (0.25 × 0.50 m) but varied in their capture system. We used targets with sticky surface (StS-targets) and those with an electrified surface (ES-targets). We also assessed the suitability of flies caught on the StS-target for molecular tests by amplifying DNA of bacterial communities. Randomized block design experiments were undertaken in Mbita area and Manga Island on Lake Victoria of western Kenya. Fly catches of each sampling tool were compared to those of the sampling tool flanked by electric (E) nets and analyzed using a negative binomial regression. The total catch for each sampling tool alone was divided by the total catch of the sampling tool flanked by two E-nets to obtain its efficiency expressed as a percentage. A proportion of flies caught on the StS-target was preserved for molecular tests. Overall, the efficiencies of the biconical trap, ES-target and StS-target were 7.7%, 13.3% and 27.0%, respectively. A higher proportion of females (69 to 79%) than males approached all the sampling tools, but the trap efficiency was greater for male G. f. fuscipes than females. Furthermore, sequencing the 16S rRNA gene from fly samples caught on the StS-target revealed the presence of Spiroplasma. Our results indicate that the SS-target is the most efficient trap to monitor G. f. fuscipes population during interventions, with the biconical trap being the least efficient, and samples collected from StS-targets are suitable for molecular studies.The European Union's integrated Biological Control Applied Research Programme (IBCARP)-tsetse repellent component; UK's Foreign, Commonwealth and Development Office (FCDO); the Swedish International Development Cooperation Agency (Sida); the Swiss Agency for Development and Cooperation (SDC); the Federal Democratic Republic of Ethiopia; and the Government of the Republic of Kenya; the University of Pretoria; the South African National Research Foundation’ IFRR.http://www.elsevier.com/locate/actatropica2022-08-10hj2021Zoology and Entomolog

Responses of Glossina fuscipes fuscipes to visually attractive stationary devices baited with 4-methylguaiacol and certain repellent compounds in waterbuck odour.

BackgroundA blend of compounds (pentanoic acid, guaiacol, δ-octalactone and geranylacetone) identified in waterbuck (Kobus defassa) body odour referred to as waterbuck repellent compounds (WRC) and a synthetic repellent 4-methylguaiacol have previously been shown to repel tsetse flies from the morsitans group. However, these repellents have not been evaluated on palpalis group tsetse flies. In this study, we evaluated the effect of these repellents on catches of Glossina fuscipes fuscipes (major vector of human sleeping sickness) in biconical traps and on sticky small targets which are visually attractive to palpalis group flies. The attractive devices were baited with different doses and blends of the repellent compounds. We also assessed the effect of removal of individual constituents in the synthetic blend of WRC on catches of G. f. fuscipes.Methodology/principal findingsThe study was conducted in western Kenya on four islands of Lake Victoria namely Big Chamaunga, Small Chamaunga, Manga and Rusinga. The tsetse fly catches from the treatments were modeled using a negative binomial regression to determine their effect on catches. In the presence of WRC and 4-methylguaiacol (released at ≈2 mg/h and ≈1.4 mg/h respectively), catches of G. f. fuscipes were significantly reduced by 33% (PConclusions/significanceWe conclude that WRC and 4-methylguaiacol reduce catches of G. f. fuscipes at stationary visually attractive traps and suggest that they may serve as broad spectrum repellents for Glossina species. We recommend further studies to investigate the effects of these compounds on reduction of G. f. fuscipes attracted to human hosts as this may lead to development of new strategies of reducing the prevalence and incidence of sleeping sickness

Responses of Glossina fuscipes fuscipes to visually attractive stationary devices baited with 4-methylguaiacol and certain repellent compounds in waterbuck odour

BACKGROUND : A blend of compounds (pentanoic acid, guaiacol, δ-octalactone and geranylacetone) identified in waterbuck (Kobus defassa) body odour referred to as waterbuck repellent compounds (WRC) and a synthetic repellent 4-methylguaiacol have previously been shown to repel tsetse flies from the morsitans group. However, these repellents have not been evaluated on palpalis group tsetse flies. In this study, we evaluated the effect of these repellents on catches of Glossina fuscipes fuscipes (major vector of human sleeping sickness) in biconical traps and on sticky small targets which are visually attractive to palpalis group flies. The attractive devices were baited with different doses and blends of the repellent compounds. We also assessed the effect of removal of individual constituents in the synthetic blend of WRC on catches of G. f. fuscipes. METHODOLOGY/PRINCIPAL FINDINGS: The study was conducted in western Kenya on four islands of Lake Victoria namely Big Chamaunga, Small Chamaunga, Manga and Rusinga. The tsetse fly catches from the treatments were modeled using a negative binomial regression to determine their effect on catches. In the presence of WRC and 4-methylguaiacol (released at ≈2 mg/h and ≈1.4 mg/h respectively), catches of G. f. fuscipes were significantly reduced by 33% (P<0.001) and 22% (P<0.001) respectively in biconical traps relative to control. On sticky small targets the reduction in fly catches were approximately 30% (P<0.001) for both 4-methylguiacol and WRC. In subtractive assays, only removal of geranylacetone from WRC significantly increased catches (by 1.8 times; P <0.001) compared to the complete blend of WRC. CONCLUSIONS/SIGNIFICANCE : We conclude that WRC and 4-methylguaiacol reduce catches of G. f. fuscipes at stationary visually attractive traps and suggest that they may serve as broad spectrum repellents for Glossina species. We recommend further studies to investigate the effects of these compounds on reduction of G. f. fuscipes attracted to human hosts as this may lead to development of new strategies of reducing the prevalence and incidence of sleeping sickness.S1 Table. Fly catches for each experiment.S2 Table. Collected data that was analysed.European Union’s integrated Biological Control Applied Research Programme; UK Department for International Development; Swedish International Development Cooperation Agency; Swedish Agency for Development and Cooperation; University of Pretoria; South African National Research Foundation’s IFRR; Kenyan Governmenthttp://journals.plos.org/plosntdshj2020Zoology and Entomolog

Effects of vector control on the population structure of tsetse (Glossina fuscipes fuscipes) in western Kenya

Displacement rates of tsetse affect performance of targets during vector control. Fly size, one of the indicators of population structure usually obtained from wing measurement, is among the determinants of displacement rates. Although recovery of tsetse in previous intervention areas has been widely reported, the population structure of tsetse that recover is rarely evaluated despite being associated with displacements rates. Previously, intervention trials had reduced tsetse densities by over 90% from >3 flies/trap/day to 9 flies/trap/day. Irrespective of sex, wing shape did not isolate tsetse based on their islands of origin. The fly size from Big and Small Chamaunga did not differ significantly before intervention trials (P = 0.728). However, three years after the intervention flies from Big Chamaunga were significantly smaller than those from Small Chamaunga (P < 0.003). Further, there was an increase in the divergence of wing morphology between flies collected from Big Chamaunga and those from Small Chamaunga after tsetse control. In conclusion, even though populations are not isolated, vector control could influence the population structure of tsetse by exerting size and wing morphology differential selection pressures. Therefore, we recommend further studies to understand the mechanism behind this as it may guide future vector control strategies.The European Union's integrated Biological Control Applied Research Programme (IBCARP) tsetse repellent component grant number IBCARP DCI-FOOD/2014/346-739; UK's Department for International Development (DFID); Swedish International Development Cooperation Agency (Sida); the Swedish Agency for Development and Cooperation (SDC); and the Kenyan Government.http://www.elsevier.com/locate/actatropica2019-03-01hj2018Zoology and Entomolog