A SMALL SCALE VARIATION IN HUMAN EXPOSURE TO MALARIA INFECTION IN KOLLA SHARA VILLAGE, SOUTHWESTERN ETHIOPIA: AN IMPLICATION FOR TARGETED MALARIA CONTROL

Abstract

Due to the decline of malaria in many countries, there is an interest to eliminate it. Hence, it is important to understand the transmission pattern of malaria to deal with the malaria foci which could be the source of infection for other community members. This study aimed to investigate the transmission patterns of malaria and to identify the sub-villages with higher risk of malaria infection towards the targeted malaria control interventions in Kolla Shara kebele (“village”), southwestern Ethiopia. Both parasitological and entomological studies were carried out from July to December, 2016 in the five sub-villages of the Kolla Shara. A total of 591 (in 90 households) study participants were followed biweekly by house to house visit for febrile cases. Blood films were collected from febrile cases for parasite detection using rapid diagnostic test (RDT) and later confirmed by microscope. Anopheles mosquito collection was done biweekly in 25 randomly selected houses (five houses in each sub-village). Plasmodium circum-sporozoite proteins (CSPs) rate of Anopheles arabiensis and An. pharoensis were tested by using Enzyme Linked Immuno-Sorbent Assay (ELISA) technique. A total of 131 febrile cases were screened for malaria using the RDT during the study period. Of these, 46 (35.1%) were microscopically confirmed malaria episodes. Plasmodium falciparum accounted for 58.7% (27/46) and 41.3% (19/46) was P. vivax malaria. The episode of P. falciparum malaria varied among the five study sub-villages. Of the 27 P. falciparum malaria episodes, 16 (59.3%) were in Abullo, 10 (37.0%) in Erze and only 1 (3.7%) episode was from Enmba sub-village. Moreover, only 30% (27/90) households (in Abullo and Erze sub-villages) experienced 80.4% (37/46) of the total malaria episodes. Although malaria episodes occurred in all age groups, the incidence was higher in children age 5-14 years with IRR: 4.1 (95% Confidence Interval (CI): 0.7-9.1); P = 0.003. Seven species of Anopheles mosquitoes were documented, of which An. arabiensis was the dominant species (70.5%), followed by An. pharoensis (10%). The highest number of Anopheles was collected from Abullo (47%; 511/1086) and Erze (32%; 348/1086) sub-villages. Of 733 Anopheles mosquitoes tested for CSPs, eight An. arabiensis were positive for P. falciparum CSP with the overall sporozoite rate of 1.1% (8/733). Abullo sub-village had CSP rate of 1.7% (5/299) and EIR of 17.0 ib/p/6 months, and in Erze sub-village, the SR was 1.4% (3/220) and its EIR was 10.6 ib/p/6 months. The overall estimated EIR of An. arabiensis was 5.7 infectious bites/person/6 months. In conclusion, malaria transmission is heterogeneous and varied between the five sub-villages in a small Kolla Shara village. Higher malaria incidence, CSP rate and EIR were observed in Abullo and Erze sub-villages. Hence, the malaria control programme could target those populations living in high malaria risky sub-villages. Moreover, intensifying the existing control interventions in these two malaria foci may make the greatest use of resources for effective malaria control.