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Entomological studies


In Ethiopia, all anophelines collected were A. gambiae s.l. (presumably A. arabiensis) except mosquitoes collected in round 4 in Hembecho which were all other anophelines. Too few mosquitoes were collected in Ethiopia to assess vector habits.


Species composition and densities

Aduku In Aduku, where mosquito densities were lower than in Butemba, A. funestus s.s. dominated during the first two surveys. Anopheles gambiae s.l. constituted 10-31% of the collections during all survey rounds. A. arabiensis was more abundant than A. gambiae s.s. during all surveys except in round 3 when A. gambiae s.s. was more common among the two species. Butemba A. gambiae s.l. was dominant and primarily consisted of A. gambiae s.s. (83-99%). A. arabiensis, A. funestus s.l. and other anophelines were collected in small numbers. All A. funestus s.l. identified (n=22) were A. funestus s.s. A. gambiae s.l. densities increased over time.



Vector biting habits

Aduku Anopheles funestus s.l. was the largest contributor to human biting rates (HBR), and readily fed both indoors and outdoors. It fed mainly early in the evening in the first round in 2012, but this behaviour was not observed in subsequent surveys. Anopheles gambiae s.l. (73% A. arabiensis and 27% A. gambiae s.s) showed a preference for biting outdoors if given equal opportunity, but the majority of contact with humans took place after 22:00. Indoor feeding occurred mostly after midnight. The biting rate decreased over the 2012-2014 period. Butemba Nearly all anophelines collected by human landing collection (HLC) were A. gambiae s.l. (97% of which were A. gambiae s.s. and 3% A. arabiensis). The large majority of feeding took place after 22:00 both indoors and outdoors. Feeding indoors continued throughout the night with peak activity observed after 02:00. Almost all human-vector contact took place indoors after 22:00. The biting rate increased between 2012 and 2014.

Entomological inoculation rates

Aduku The entomological inoculation rate (EIR), which measures transmission intensity in terms of number of infective bites per unit time, was highest in rounds 1 and 3 (0.19 and 0.14 per person per night, respectively) but declined significantly in round 4 (0.01 bites per person per night). Butemba The EIR increased from 0.05 to 0.10 bites per person per night from 2012-14. Less

Insecticide resistance

Aduku There was no evidence of bendiocarb resistance in A. arabiensis during rounds 1 and 2, but suspected resistance was detected in rounds 3 and 4. There was no resistance detected against pirimiphos-methyl. In rounds 1 and 4, tests primarily with A. arabiensis showed susceptibility to pyrethroids. However, tests in rounds 2 and 3 showed suspected or confirmed resistance. Anopheles arabiensis was susceptible to permethrin but A. gambiae s.s. was found to be resistant to the chemical. A. gambiae s.s. collected by various trapping techniques showed a high frequency of kdr-L1014S (81-100%), whereas those from the resistance tests showed varying levels (42-87%). A. gambiae s.s. that survived exposure to pyrethroids had a significantly higher kdr-L1014S genotype frequency than non-survivors. kdr-L1014F mutation was observed in low frequencies (0.9-2.3%) in A. arabiensis. No acetylcholinesterase (ace-1 G119S) target mutation was detected in both A. gambiae s.s. and A. arabiensis. Butemba No resistance of A. gambiae s.s. was detected against bendiocarb or pirimiphos-methyl. Susceptibility tests indicated high levels of A. gambiae s.l. resistance against pyrethroids. kdr-L1014S frequencies were uniformly high (>90%) in A. gambiae s.s. In contrast, almost all A. arabiensis analysed were homozygous susceptible at the kdr-L1014S locus. When mosquitoes were pre-exposed to the synergist piperonyl butoxide (PBO), mortality increased after exposure to deltamethrin or permethrin, suggesting some contribution of a metabolic resistance mechanism to the observed resistance. No A. arabiensis survived following PBO pre-exposure suggesting that this mechanism is stronger in this species compared to A. gambiae s.s. A. gambiae s.s. survivors of tests with pyrethroids had significantly higher kdr frequencies, although the frequencies were also high in non-survivors. The kdr-L1014F mutation frequency was 15.0% and 8.2% in rounds 3 and 4, respectively. No ace-1 G119S mutation was detected in both A. gambiae s.s. and A. arabiensis.  


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