78 research outputs found
Biting Hour and Host Seeking Behavior of <i>Aedes</i> Species in Urban Settings, Metema District, Northwest Ethiopia
No full textBackground: Aedes species transmit arboviral diseases, such as dengue, chikungunya, yellow fever, and Zika. The diseases cause severe sickness, mortality, and economic losses. This study describes the biting hour and host-seeking behavior of Ae. aegypti and Ae. vittatus in three towns. Recently, chikungunya and dengue infections were reported in the study sites. Methods: Biting hour and host-seeking behaviors of Ae. aegypti and Ae. vittatus were studied from June to September 2023, in Genda-Wuha, Kokit, and Metema-Yohannes towns, Metema district, Northwest Ethiopia. CDC-LT traps were set running indoors and outdoors for 24 h closer to humans sleeping inside unimpregnated mosquito nets. At the same time, CDC-LT traps were set running overnight closer to domestic animals’ shelters located within a 50-m radius of the main residence. Mosquitoes trapped in CDC-LT were collected every hour. The study was conducted four times in each town during the wet season. A chi-square test was employed to examine biting hour and host-seeking behavior. Results: Aedes aegypti was observed to be highly exophilic and active during the daylight hours. Aedes aegypti exhibited a peak biting rate between 07:00 and 08:00 with the biting rate of 4.5/person/hour followed by from 17:00 pm to 18:00 pm with the biting rate of 3.75/person/hour. The hourly biting rate of Ae. aegypti differed significantly. Its peak indoor biting rate was from 19:00 to 20:00 with the rate of 2.00 bites/person/hour followed by from 08:00 to 09:00 with the rate of 1.50 bites/person/hour and the biting rates differed significantly across the hours (F = 240.046; p = 0.001). Aedes vittatus also exhibited a biting rate similar to that of Ae. aegypti. Both Ae. aegypti and Ae. vittatus were abundantly collected from nearby human sleeping arrangements than from the shelters of cattle, sheep, goats, and donkeys. The highest proportions of Ae. aegypti (91.21%) and Ae. vittatus (89.87%) were unfed. Conclusions: Aedes aegypti and Ae. vittatus exhibited peak biting rates during morning and early night hours that aligned with the active daily routine practices of the local community. This could potentially expose the inhabitants to viral diseases transmitted by Ae. aegypti and Ae. vittatus
Physical and chemical characteristics of Aedes larval habitats in Metema District, Northwest, Ethiopia
No full textAbstract Background Aedes-transmitted viral diseases such as dengue, chikungunya, yellow fever, and Zika are increasing public health and economic challenge globally. In the absence of treatments and vaccines for arboviral diseases, surveillance and control of Aedes larvae remains a top priority. However, Aedes larvae control strategies relay to a large extent on the knowledge of the distribution and characteristics of their habitats. The study assessed habitats, indices, habitat physico-chemical characteristics and composition of Aedes larvae and pupae in three towns. Methods Aedes larvae and pupae were collected in Metema-Yohannes, Kokit, and Gendawuha towns of northwestern Ethiopia, from January 2022 to December 2023 following standard procedures. Aedes larvae/pupae were surveyed along natural and artificial habitats in relation to residential houses, physico-chemical characteristics of habitats characterized, reared to adults and later identified to species based on their morphological features. Data were entered and analyzed using IBM SPSS version 20.0. Results Aedes larvae and pupae were abundant in Metema-Yohannes, Kokit and Gendawuha towns. Breteau, house, and container indices exceeded the World Health Organization's risk levels for arboviral diseases. Density of Aedes larvae/pupae was positively correlated with habitat water temperature, conductivity, phosphate, ammonia, total hardness and sulphate both in the artificial and natural habitats (P < 0.001). Adult Ae. aegypti were the most abundant (56.77%; 5106/8993) that emerged from larvae/pupae followed by Ae. vittatus (37.25%; 3350/8993), Ae. communis (2.39%; 215/8993), Ae. opok (0.66%; 60) and Ae. albopictus (0.26; 24). The number of Ae. aegypti emerged from algal habitats was greater than the number from the algae free (p < 0.001) and the number from tadpole free habitats was greater than the number from tadpole infested (p < 0.001). Adults of Ae. vittatus followed a similar trend. The mean number of Ae. aegypti emerged from larvae/pupae of habitats closer to human habitations, not exposed to sunlight, free of emergent vegetation and tyre substrates were significantly (p < 0.001) higher than from habitats of corresponding attributes. Conclusion Artificial water-holding containers maintained higher density of Aedes larvae/pupae than natural water-holding containers in Metema-Yohannes, Kokit and Gendawuha towns. Ae. aegypti, Ae. vittatus, Ae. communis, Ae. albopictus and Ae. opok occurred in the towns. Ae. aegypti and Ae. vittatus larvae/pupae were abundant in discarded tyres, Ae. communis in discarded metal containers, and Ae. albopictus and Ae. opok in tree holes during the wet seasons in Metema Woreda, Northwestern Ethiopia. This study indicates the importance of improving Aedes larvae/pupae surveillance and control measures in Metema Woreda, Northwest Ethiopia
Evaluation of the influence of electric nets on the behaviour of oviposition site seeking Anopheles gambiae s.s
No full textBackground:
Electric nets (e-nets) are used to analyse the flight behaviour of insects and have been used extensively to study the host-oriented flight of tsetse flies. Recently we adapted this tool to analyse the oviposition behaviour of gravid malaria vectors, Anopheles gambiae s.s., orienting towards aquatic habitats and traps by surrounding an artificial pond with e-nets and collecting electrocuted mosquitoes on sticky boards on the ground next to the nets. Here we study whether e-nets themselves affect the responses of gravid An. gambiae s.s..
Methods:
Dual-choice experiments were carried out in 80 m2 screened semi-field systems where 200 gravid An. gambiae s.s. were released each night for 12 nights per experiment. The numbers of mosquito landing on or approaching an oviposition site were studied by adding detergent to the water in an artificial pond or surrounding the pond with a square of e-nets. We also assessed whether the supporting framework of the nets or the sticky boards used to retain electrocuted mosquitoes influenced the catch.
Results:
Two similar detergent treated ponds presented in choice tests caught an equal proportion of the mosquitoes released, whereas a pond surrounded by e-nets caught a higher proportion than an open pond (odds ratio (OR) 1.7, 95% confidence interval (CI) 1.1 - 2.7; p < 0.017). The separate evaluation of the impact of the square of electric nets and the yellow boards on the approach of gravid females towards a pond suggests that the tower-like construction of the square of electric nets did not restrict the approach of females but the yellow sticky boards on the ground attract gravid females to a source of water (OR 2.7 95% CI 1.7 – 4.3; p < 0.001).
Conclusion:
The trapping efficiency of the electric nets is increased when large yellow sticky boards are placed on the ground next to the e-nets to collect electrocuted mosquitoes, possibly because of increased visual contrast to the aquatic habitat. It is therefore important when comparing two treatments that the same trapping device is used in both. The importance of contrast around artificial habitats might be exploited to improve collections of An. gambiae s.s. in gravid traps
ANALYSES OF TEN-YEAR MALARIA TRANSMISSION DYNAMICS IN RELATION TO METEOROLOGICAL VARIABLES IN JABI TEHNAN DISTRICT, NORTHWEST ETHIOPIA
No full textRetrospective studies of malaria cases from health facilitiesand the impact of meteorological factors provide insight into the dynamics ofmalaria transmission and the effectiveness of malaria control interventions.This study aimed to analyze inter-annual and monthly trends in malaria casesand determine the correlations between meteorological variables andprevalence of malaria. Retrospective data on malaria cases were extractedfrom 11 health centres and 39 health posts in Jabi Tehnan district, northwestEthiopia, for 10 years (July 2011–May 2021). Trends in monthly and annualmalaria cases were analyzed and correlated with meteorological data. Of1,500,868 individuals with febrile complaints examined at the health facilitiesin the district, 13.4% were diagnosed as clinical malaria cases. Furthermore,12.6% of those with febrile symptoms had malaria confirmed withmicroscopy and with rapid diagnostic test (RDT). Plasmodium falciparumcomprised 56.48%, with 36.56% P. vivax, and with 6.96% mixed (P.f + P.v)infections. There were significant variations in inter-annual and monthlymalaria cases (P<0.001; P = 0.004, respectively). Malaria cases peaked in2011–2013, and 2015–2016, with reduced and relatively lower malaria casesin 2017–2021. Two malaria peaks in May-June, and in October-Novemberwere recorded. Inter-annual and monthly malaria trends were closelycorrelated with relative humidity and average temperatures. Plasmodiumfalciparum was predominant compared to P. vivax. Understanding trends inmalaria transmission in relation to climatic variables, and monitoring theeffectiveness of malaria control interventions are needed to reduce malaria inthe area
Malaria Vectors Tend to Avoid the Indoor-Based Vector Control Tools in Wonji Sugar Estate, Oromia, Ethiopia
No full textBackground: There is a paucity of data regarding resting habits and comparison of the physiological states of Anopheles mosquito populations from indoor and outdoor collection venues in Ethiopia. Therefore, this study aims to investigate resting behavior and age structure of the malaria vectors in Wonji Sugar Estate. Methods: Longitudinal entomological study was conducted at Wonji Sugar Estate from July 2018 to June 2020. Pyrethrum spray catches (PSC), Pit Shelter (PIT), and Oral Aspirators were used to collect adult Anopheles species from various resting sites. Mosquitoes were identified to the species using morphological keys. Finally, the resting behavior of Anopheles mosquitoes were determined using standard protocol. Results: A total of 1406 mosquitoes were collected from indoor and outdoor resting venues, with the outdoor resting population being significantly higher ( F = 8.296, P = .04). The number of half-gravid/gravid Anopheles species collected from outdoors was higher than that from indoor resting venues ( F = 35.612, P = .00). Eight two percent of the indoor sampled Anopheles species left the indoor venue before completing their gonotrophic cycle. Anopheles pharoensis and An. coustani cx. exhibited exophily rate of 83.4% and 100%, respectively. The overall parity rate of Anopheles gambiae s.l. was 45.7%. The highest parity rate, daily survival rate, and longevity of Anopheles gambiae s.l. was 66.7%, 0.874, and 7.399 days, respectively. Anopheles gambiae s.l. reached the infective stages for Plasmodium falciparum and P. vivax in February 2019. Conlusion: Anopheles mosquitoes, including the major malaria vector Anopheles gambiae s.l., showed predominantly exophilic habits, underscoring the need for outdoor vector control strategies in addition to indoor-based interventions. The increase in the nulliparous population indicates a higher risk of vector-human contact. Meanwhile, the extended lifespan of Anopheles gambiae s.l. observed during the dry season could increase the risk of infectious bites
A survey of malaria vectors feeding preference, biting site and resting behaviour in the malaria elimination settings of Dembiya District, north-western Ethiopia
No full textAbstract Background Despite the progress in scaling vector control interventions in Ethiopia, malaria is still a major health problem in the country. Monitoring of the local vector populations and the effectiveness of vector control strategies is necessary to guide programme decisions to optimize malaria prevention efforts. This study investigated the feeding preference, the biting behaviour and resting behaviours of Anopheles mosquitoes in selected localities of Dembiya District. Methods Adult Anopheles mosquitoes were sampled indoors and outdoors from June 2018 to May 2019 using CDC light traps, pyrethrum spray catches, artificial pit shelters, and mouth aspirators at both Guramba Bata and Arebiya study sites. Anopheles mosquitoes were identified to the species level. Their blood meal source and Plasmodium sporozoite infections were determined using an enzyme-linked immunosorbent assay. Results Anopheles mosquitoes belonging to 11 species were identified from 2,055 collected mosquito specimens. Anopheles pharoensis was the predominant species at both the Guramba Bata (46.5%) and Arebiya (46.2%) study sites. The CDC light traps caught the highest number of Anopheles mosquitoes in both study sites. In Guramba Bata the density of outdoor host-seeking and resting Anopheles mosquitoes were higher than indoors (P ≤ 0.05). The human blood indexes (HBI) of indoor and outdoor host-seeking Anopheles arabiensis were 17.4% and 15.3%, respectively. The entomological inoculation rate (EIR) of outdoor host-seeking An. arabiensis was 4.7 infective bites/person/year. Additionally, the outdoor EIR of host-seeking Anopheles coustani was 25.7ib/p/year. Conclusions Anopheles mosquitoes in Dembiya district were more likely to seek a host and rest outdoors than indoors. A reevaluation of vector control strategies is needed to ensure Ethiopia remains on the path to malaria elimination. The detection of Plasmodium circumsporozoite protein in potential secondary vectors, such as An. coustani requires further investigation to substantiate their role in malaria transmission
Mosquito odour-baited mass trapping reduced malaria transmission intensity: a result from a controlled before-and-after intervention study
No full textBackground
Conventional vector control strategies have significantly reduced the malaria burden. The sustainability of these methods is currently challenged. Odour-based traps are emerging technologies that can complement the existing tools. Implementation of odour-based traps for mass trapping is limited due to the restricted range of vectors caught with available carbon dioxide-dependent lures, and the lack of comprehensive field studies. The objective of this study was to assess the impact of odour-mediated mass trapping targeting outdoor vectors, using a synthetic cattle urine lure that attracts a wide range of vector species in a variety of physiological states, on malaria prevalence and entomological parameters to determine malaria transmission intensities.
Methods
A controlled before-and-after study was conducted in two rural communities in southern Ethiopia. Baseline monthly entomological and seasonal cross-sectional malaria prevalence surveys were conducted in both communities for a year. Then, mass trapping of mosquitoes was conducted in one of the villages, while the monthly entomological surveillance and seasonal malaria prevalence surveys continued in both villages. Generalised linear mixed models were constructed and tested to determine which factors were significantly affected by the intervention.
Results
Mass trapping contributed to the reduction of the population of the principal malaria vector, Anopheles arabiensis, and the associated entomological indicators, the human bite rate (HBR) and the entomological inoculation rate (EIR), in the intervention village compared to the control village. The intervention village had an average HBR by An. arabiensis of 3.0 (95% CI 1.4–4.6) during the peak malaria transmission season, compared to 10.5 (95% CI − 0.5–21.5; P < 0.0001) in the control village. The intervention village (mean 0.02, 95% CI − 0.05–0.4.8) had a daily EIR eight times lower than the control village (mean 0.17, 95% CI), which likely contributed to the reduced malaria prevalence in the intervention community following its introduction by ca. 60% (95% CI 55–63).
Conclusions
The combined use of odour-based mass trapping and conventional control strategies coincided with a reduction of human-vector contact and malaria prevalence, providing support for odour-baited technologies as a viable option for next-generation vector control tools. Further cluster-randomised control studies are recommended in different eco-epidemiological settings with varying malaria transmission intensities
Field evaluation of two novel sampling devices for collecting wild oviposition site seeking malaria vector mosquitoes: OviART gravid traps and squares of electrocuting nets.
No full textBACKGROUND: New sampling tools are needed for collecting exophilic malaria mosquitoes in sub-Saharan Africa to monitor the impact of vector control interventions. The OviART gravid trap and squares of electrocuting nets (e-nets) were recently developed under semi-field conditions for collecting oviposition site seeking Anopheles gambiae (sensu stricto) (s.s.). This study was designed to evaluate the efficacy of these traps for sampling malaria vectors under field conditions. METHODS: Prior to field testing, two modifications to the prototype OviART gravid trap were evaluated by (i) increasing the surface area and volume of water in the artificial pond which forms part of the trap, and (ii) increasing the strength of the suction fan. Six sampling tools targeting gravid females (Box gravid trap, detergent-treated ponds, e-nets insect glue-treated ponds, sticky boards and sticky floating-acetate sheets) were compared under field conditions to evaluate their relative catching performance and to select a method for comparison with the OviART gravid trap. Finally, the trapping efficacy of the OviART gravid trap and the square of e-nets were compared with a Box gravid trap during the long rainy season in three household clusters in western Kenya. RESULTS: The OviART gravid trap prototype's catch size was doubled by increasing the pond size [rate ratio (RR) 1.9; 95 % confidence interval (CI) 1.1-3.4] but a stronger fan did not improve the catch. The square of e-nets performed better than the other devices, collecting three times more gravid Anopheles spp. than the Box gravid trap (RR 3.3; 95 % CI 1.4-7.6). The OviART gravid trap collections were comparable to those from the e-nets and 3.3 (95 % CI 1.5-7.0) times higher than the number of An. gambiae senso lato (s.l.) collected by the Box gravid trap. CONCLUSION: Both OviART gravid trap and squares of e-nets collected wild gravid Anopheles gambiae (s.l.) where natural habitats were within 200-400 m of the trap. Whilst the e-nets are difficult to handle and might therefore only be useful as a research device, the OviART gravid trap presents a promising new surveillance tool. Further field testing is needed in different eco-epidemiological settings to provide recommendations for its use
Malaria hotspots explained from the perspective of ecological theory underlying insect foraging
No full textHotspots constitute the major reservoir for residual malaria transmission, with higher malaria incidence than neighbouring areas, and therefore, have the potential to form the cornerstone for successful intervention strategies. Detection of malaria hotspots is hampered by their heterogenous spatial distribution, and the laborious nature and low sensitivity of the current methods used to assess transmission intensity. We adopt ecological theory underlying foraging in herbivorous insects to vector mosquito host seeking and modelling of fine-scale landscape features at the village level. The overall effect of environmental variables on the density of indoor mosquitoes, sporozoite infected mosquitoes, and malaria incidence, was determined using generalized linear models. Spatial analyses were used to identify hotspots for malaria incidence, as well as malaria vector density and associated sporozoite prevalence. We identify household occupancy and location as the main predictors of vector density, entomological inoculation rate and malaria incidence. We propose that the use of conventional vector control and malaria interventions, integrated with their intensified application targeting predicted hotspots, can be used to reduce malaria incidence in endemic and residual malaria settings
Comparative performance of microscopy, rapid diagnostic tests, and multiplex real-time PCR for detection of malaria parasites among pregnant women in northwest Ethiopia
No full textAbstract Background Low malaria parasitaemia is a diagnostic challenge in pregnancy, leading to false negative microscopy and rapid diagnostic test (RDT) results. However, these submicroscopic or subpatent infections could cause adverse pregnancy outcomes. Thus, evaluating the diagnostic performance of microscopy, RDT, and multiplex qPCR in pregnancy is vital for informed decisions. Methods A total of 835 peripheral blood and 372 placental blood samples were collected from 835 pregnant women attending first antenatal care or admitted for delivery at selected health facilities in northwest Ethiopia between November 2021 and July 2022. In multiplex qPCR, all microscopy and/or RDT positive samples were extracted and amplified individually, whereas all samples negative by both RDT and microscopy were extracted after pooling ten samples together and tested for Plasmodium genus. The diagnostic performance of microscopy, RDT, and multiplex qPCR in pregnancy was compared and evaluated against each other. Results Using multiplex qPCR as a reference test, microscopy had a sensitivity of 73.8% (95% confidence interval (CI): 65.9–80.7) and 62.2% (95% CI: 46.5–76.2) to detect Plasmodium parasites in peripheral and placental blood samples, respectively, with a 100% (95% CI: 98.9–100) specificity in both samples. Similarly, the RDT had a sensitivity of 67.6% (95% CI: 59.3–75.1) and a specificity of 96.5% (95% CI: 94.9–97.8) for Plasmodium infection diagnosis in peripheral blood and a sensitivity of 62.2% (95% CI: 46.5–76.2) and a specificity of 98.8% (95% CI: 96.9–99.7) in placental blood samples. Considering microscopy as a reference test, multiplex qPCR showed a sensitivity of 100% (95% CI: 96.6–100) and a specificity of 94.8% (95% CI: 93.0–96.3) to diagnose Plasmodium infections in both peripheral and placental blood samples. Pooled multiplex qPCR detected 34 peripheral and 12 placental blood Plasmodium infections from microscopy and RDT negative samples. The pooled assay obviated about half of the reactions and its testing costs. Microscopy showed almost perfect agreement (κ = 0.823) with multiplex qPCR for detecting malaria parasites in pregnancy, whereas the RDT showed a substantial agreement (κ = 0.684). Conclusion Multiplex qPCR had a better performance for Plasmodium infection diagnosis in pregnancy compared to microscopy and RDT. Pooled multiplex qPCR could be a sensitive and resource-efficient strategy for epidemiological surveillance of Plasmodium infections in pregnancy
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