Month: March 2015

Entomological collections in areas targeted for a cluster randomized controlled trial to prevent malaria in Ethiopia: Results from a pilot study

Oljira Kenea1, Meshesha Balkew1, Teshome Gebre-Micheal1, Taye Gari2, Eskindir Loha2, Wakgari Deressa1,Alemayehu Dessalegn1, Bjarne Robberstad3, Hans J Overgaard4, Bernt Lindtjørn3

1 Addis Ababa University, Addis Ababa, Ethiopia.2HawassaUniversity, Hawassa, Ethiopia. 3University of Bergen, Bergen, Norway.4Norwegian University of Life Sciences, Ås, Norway.

Objective  Indoor residual spraying (IRS) and long-lasting insecticidal nets (LLINs) are the core malaria vector control tools in Ethiopia. Combining both in the same household as a vector control strategy is widespread but entomological outcomes of such interventions are little known. This pilot study was carried out to provide basic information about local malaria vector population for effective planning and implementation of IRS and LLINs cluster randomized trial.

Methodology  The study was conducted from June to October 2013 in Adami Tulu district, central Ethiopia. Indoor mosquito collections were done using CDC light traps and pyrethrum spray sheet catches. Outdoor collections were done from artificial pit shelters. Mosquitoes were identified to species by morphological characteristics and polymerase chain reaction (PCR). Enzyme-linked immunosorbent assays (ELISA) were carried out to detect the sources of host blood meals and circum-sporozoite proteins. Mosquito longevity was estimated using parity based on dilatation of ovarian tracheoles following dissection. Data were managed and analyzed using SPSS version 20.0 and a p value< 0.05 was considered to be statistically significant.

Results  All Anopheles gambiae mosquitoes were confirmed to be An. arabiensis by PCR. Of 232 adult Anopheles mosquitoes collected, An. arabiensis (71.1%) was the predominant species followed by An. pharoensis (21.1%). The overall average Anopheles density varied within and among the villages over the study months. All of the mosquitoes (n = 232) that were analyzed by ELISA were negative for Plasmodium falciparum and P. vivax circum-sporozoite proteins. The overall Human Blood Index (69.2%) for An. arabiensis was higher than Bovine Blood Index (38.4%) and it was higher for populations collected indoors (73%) than those collected outdoors (21%). Average longevity of An. arabiensis and An. pharoensis ranged from 7 to 25 and 1.6 to 6.3 days, respectively.

Conclusion  The density of An. arabiensis, the main malaria vector in Ethiopia, varied within and among the villages over the study months. This study provided preliminary information needed for effective planning and implementation of LLINs and IRS combined intervention trial against malaria in Adami Tulu district, central Ethiopia.

Malaria incidence in areas targeted for a cluster randomised controlled trial to prevent malaria in Ethiopia: Results from a pilot study

Taye Gari1, Eskindir Loha1, Wakgari Deressa 2, Alemayehu Hailu 2, Oljira Kenea 2, Meshesha Balkew2, Teshome Gebremichael 2, Bjarne Robberstad3, Hans J Overgaard 4,5, Bernt Lindtjørn 3
1 Hawassa University, Hawassa, Ethiopia. 2 Addis Ababa University, Addis Ababa, Ethiopia. 3University of Bergen, Bergen, Norway. 4Norwegian University of Life Sciences, Ås, Norway. 5 Institut de Recherche pour le Développement (IRD), MIVEGEC, Montpellier, France.

MalTrials project funded by RCN GLOBVAC, Norway (project no. 220554)

Objective  A cluster randomised controlled trial will be carried out in central Ethiopia to evaluate the effect of combining indoor residual spraying (IRS) and long-lasting insecticidal treated nets (LLIN) on reducing malaria incidence. A pilot study was conducted to assess the variation in malaria episodes within and among villages. Information from this pilot study will serve as the baseline and for calculation of a sufficient sample size to detect significant differences in malaria episode between study arms of the trial.

Method  A cohort of 5309 residents from 994 households in 29 villages were followed from August to December, 2013 in Adami Tulu district in central Ethiopia. The villages were selected based on average distance from Ziway lake shore where the majority of malaria mosquito breeding sites are located. A household census was done, followed by weekly home visits to collect malaria related data. Blood samples were taken from febrile patients. Microscopic slide examination was performed for malaria parasite identification. Incidence rate of malaria episodes was calculated.

Results  Only 271 (27.3%) of the households owned at least one insecticidal treated net at the start of the pilot study. The average proportion of residents sleeping under LLIN the night before the visit was 2.7%. Indoor residual spray was carried out in 901 (91.7%) households within one year before the visit. Of 349 persons examined 39(11.2%) were positive for malaria parasite. Plasmodium vivax was the dominant (84.6%) cause of malaria infection. The average incidence of malaria episode was 4.6 (varied among villages from 0 to 23.4 episodes) per 10,000 person weeks of observation. Higher malaria incidence was observed among children under 5, 5-14 years and in villages near the lake shore with 6.8, 6.3 and 8 episodes per 10,000 person weeks, respectively. The intra-cluster-correlation coefficient of malaria episodes was 0.27.

Conclusion  This pilot study showed that the incidence of malaria was higher in villages near the lake shore and in children less than 15 years old than the average incidence rate. The variation in malaria incidence between villages will be considered to calculate an appropriate sample size for the main trial.