Browsing by Author "Kenea, Oljira"

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    Entomological Impact of Combined and Separate Use of Indoor Residual Spraying and Long-Lasting Insecticidal Nets for Malaria Prevention in Adami Tullu District, South-Central Ethiopia
    (Addis Ababa University, 2016-02-03) Kenea, Oljira; Tekie, Habte
    Indoor residual spraying (IRS) and long-lasting insecticidal nets (LLINs) are the key frontline malaria prevention interventions in Ethiopia. Both target Anopheles arabiensis, the sole primary malaria vector. Universal coverage of both interventions has been promoted and there is a growing demand in combination of interventions for malaria control and elimination. However, available evidence is contradictory wether the combined intervention is better than either IRS or LLINs alone. To investigate whether IRS and LLINs combination provides added protective impact on An. arabiensis compared to either IRS or LLINs alone, a cluster randomized controlled trial was carried out in Adami Tullu district, south-central Ethiopia. Villages were randomly allocated to four study arms: IRS+LLINs, IRS, LLINs, and control. All households in the IRS+LLINs and LLINs arms were provided with LLINs (PermaNet 2.0) free of charge. Households in the IRS+LLINs and IRS arms were applied with propoxur before the main malaria transmission season in 2014 and 2015. Adult mosquitoes were collected in randomly selected villages in each arm using CDC light trap catch (LTC) set close to a sleeping person, pyrethrum spray catch (PSC), and artificial pit shelter (PIT), for measuring host-seeking density (HSD), indoor resting density (IRD), and outdoor resting density (ORD) of the anophelines. Human landing catch (HLC) was performed in selected villages to monitor the impact of the interventions on local mosquito biting behaviours (biting location, time and host preference). Collected anophelines were identified to species by use of standard morphological keys and additional use of molecular methods to separate sibling species of the An. gambiae complex. Enzyme-linked immunosorbent assay (ELISA) was used to detect malaria infections in mosquitoes and the sources of mosquito blood meals. Mean densities were compared using incidence rate ratio (IRR) calculated by negative binomial regression. Parity rate (percentage of xxii parous females) was also determined by ovarial dissection. Human blood index (HBI) was expressed as the proportion of mosquitoes with human blood divided by the total number of blood-fed mosquitoes tested. A total of 1786 female anophelines of four species (An. arabiensis, An. pharoensis, An. ziemanni and An. funestus s.l.) were collected over two transmission seasons during the intervention period (2014-2015). Anopheles numbers were highest in the control arm (41.3% of total) followed by LLINs (25.4%), IRS (18.0%), and IRS+LLINs (15.8%). In most of the vector parameters estimated, the impact of IRS and LLINs combined and separate interventions were significantly higher in communities that recieved the interventions (in experimental groups) compared with untreated communities (control group). The mean HSD of An. arabiensis in the IRS+LLINs arm was similar to the IRS arm (0.03 vs. 0.03/ house/LTC/night) but lower than the LLINs arm (0.03 vs. 0.10/house/LTC/night, p=0.07) and so was the difference in IRD and ORD between the IRS+LLINs compared to the IRS arm. However, both IRD and ORD of An. arabiensis were higher in LLINs compared to IRS+LLINs (p < 0.001 for indoors). Parity rate of An. arabiensis were similar among the intervention arms. None of the 1786 samples of four species tested by ELISA was positive for P. falciparum and P. vivax CSP infection in all of the study arms. Anopheles arabiensis preferred mainly bovine and human hosts for blood meal sources with high HBI in the LLIN alone. Indoor resting habit of An. arabiensis was less impacted by LLINs alone intervention compared to IRS + LLINs or IRS alone. In conclusion, the IRS+LLINs and the IRS alone each was similarly most effective against An. arabiensis as compared to the LLINs alone. The IRS+LLINs provided added impact on An. arabiensis compared to LLINs alone. The LLINs alone had poor impact on densities and human biting rates of An. arabiensis in this study setting.
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    Entomological Impact of Combined and Separate Use of Indoor Residual Spraying and Long-Lasting Insecticidal Nets for Malaria Prevention in Adami Tullu District, South-Central Ethiopia
    (Addis Ababa University, 2016-06) Kenea, Oljira; Tekie, Habte(PhD)
    Indoor residual spraying (IRS) and long-lasting insecticidal nets (LLINs) are the key frontline malaria prevention interventions in Ethiopia. Both target Anopheles arabiensis, the sole primary malaria vector. Universal coverage of both interventions has been promoted and there is a growing demand in combination of interventions for malaria control and elimination. However, available evidence is contradictory wether the combined intervention is better than either IRS or LLINs alone. To investigate whether IRS and LLINs combination provides added protective impact on An. arabiensis compared to either IRS or LLINs alone, a cluster randomized controlled trial was carried out in Adami Tullu district, south-central Ethiopia. Villages were randomly allocated to four study arms: IRS+LLINs, IRS, LLINs, and control. All households in the IRS+LLINs and LLINs arms were provided with LLINs (PermaNet 2.0) free of charge. Households in the IRS+LLINs and IRS arms were applied with propoxur before the main malaria transmission season in 2014 and 2015. Adult mosquitoes were collected in randomly selected villages in each arm using CDC light trap catch (LTC) set close to a sleeping person, pyrethrum spray catch (PSC), and artificial pit shelter (PIT), for measuring host-seeking density (HSD), indoor resting density (IRD), and outdoor resting density (ORD) of the anophelines. Human landing catch (HLC) was performed in selected villages to monitor the impact of the interventions on local mosquito biting behaviours (biting location, time and host preference). Collected anophelines were identified to species by use of standard morphological keys and additional use of molecular methods to separate sibling species of the An. gambiae complex. Enzyme-linked immunosorbent assay (ELISA) was used to detect malaria infections in mosquitoes and the sources of mosquito blood meals. Mean densities were compared using incidence rate ratio (IRR) calculated by negative binomial regression. Parity rate (percentage of xxii parous females) was also determined by ovarial dissection. Human blood index (HBI) was expressed as the proportion of mosquitoes with human blood divided by the total number of blood-fed mosquitoes tested. A total of 1786 female anophelines of four species (An. arabiensis, An. pharoensis, An. ziemanni and An. funestus s.l.) were collected over two transmission seasons during the intervention period (2014-2015). Anopheles numbers were highest in the control arm (41.3% of total) followed by LLINs (25.4%), IRS (18.0%), and IRS+LLINs (15.8%). In most of the vector parameters estimated, the impact of IRS and LLINs combined and separate interventions were significantly higher in communities that recieved the interventions (in experimental groups) compared with untreated communities (control group). The mean HSD of An. arabiensis in the IRS+LLINs arm was similar to the IRS arm (0.03 vs. 0.03/ house/LTC/night) but lower than the LLINs arm (0.03 vs. 0.10/house/LTC/night, p=0.07) and so was the difference in IRD and ORD between the IRS+LLINs compared to the IRS arm. However, both IRD and ORD of An. arabiensis were higher in LLINs compared to IRS+LLINs (p < 0.001 for indoors). Parity rate of An. arabiensis were similar among the intervention arms. None of the 1786 samples of four species tested by ELISA was positive for P. falciparum and P. vivax CSP infection in all of the study arms. Anopheles arabiensis preferred mainly bovine and human hosts for blood meal sources with high HBI in the LLIN alone. Indoor resting habit of An. arabiensis was less impacted by LLINs alone intervention compared to IRS + LLINs or IRS alone. In conclusion, the IRS+LLINs and the IRS alone each was similarly most effective against An. arabiensis as compared to the LLINs alone. The IRS+LLINs provided added impact on An. arabiensis compared to LLINs alone. The LLINs alone had poor impact on densities and human biting rates of An. arabiensis in this study setting.
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    Environmental Factors Associated with Larval Habitats of Anopheline Mosquitoes (Diptera: Culicidae) in Irrigation and Major Drainage Areas Between Adami Tulu and Meki Towns, Central Ethiopia
    (Addis Ababa University, 2008-07) Kenea, Oljira; Gebre-Michael, Teshome (PhD)
    A study was conducted to characterize larval habitats of anopheline mosquitoes in irrigation and major drainage areas between Adami Tulu and Meki towns, in the middle course of the Ethiopian Reft Valley. A total of 22 anopheline larval positive aquatic habitats were sampled fortnightly from late December 2007 to early June 2008 by using dipping techniques. Simultaneously, environmental variables of the larval habitats were also measured/estimated and recorded. A total of 3,439 anopheline and 5,213 culicine larvae were collected. Microscopic identification of the late instars (3rd and 4th) of anopheline larvae yielded 47.6% of An. pharoensis, 32.1% An. gambiae s.l. larvae (presumably An. arabiensis) and only 20.3% other anopheline larval species (An. squamosus, An. coustani and An. cinereus). Anopheles larvae were sampled predominantly from natural swamps, irrigation canals and sand pools with samples from these habitat types representing 88.0% (3025) of the total anopheline larval collection in the study area. Larvae of the malaria vector species, An. gambiae s.l. (An. arabiensis) and An. pharoensis were most frequently sampled from sand pools and natural swamps, respectively. The habitats were characterized based on water temperature, turbidity, water current, water pH, elevation, aquatic vegetation, habitat permanence, origin of the habitats (natural or human made), distance to the nearest house, presence of mats of algae, water depth, intensity of shade, and substrate type. Logistic regression analysis detected six key environmental variables that were associated with the occurrence/abundance of anopheline larvae: Water temperature, presence of mats of algae, water depth, and origin of the habitats, turbidity and water current. Multiple step-up regression analysis further detected four best predictor variables associated with larval abundance of the malaria vector species. Accordingly, relative abundance of An. gambiae s.l. larvae was significantly and inversely associated with aquatic vegetation and water current whereas that of An. pharoensis larvae were significantly and positively associated with water temperature and the presence of algae in the water bodies. Dry season anopheline larval habitats that are created and maintained by perenial water bodies such as the Ethiopian Rift Valley lakes and rivers and their associated water development projects need to be considered in vector control operation and further research.