TY - JOUR
T1 - Does insecticide resistance contribute to heterogeneities in malaria transmission in The Gambia?
AU - Opondo, Kevin Ochieng
AU - Weetman, David
AU - Jawara, Musa
AU - Diatta, Mathurin
AU - Fofana, Amfaal
AU - Crombe, Florence
AU - Mwesigwa, Julia
AU - D'Alessandro, Umberto
AU - Donnelly, Martin
PY - 2016/3/15
Y1 - 2016/3/15
N2 - BACKGROUNDMalaria hotspots, areas with consistently higher than average transmission, may become increasingly common as malaria declines. This phenomenon, currently observed in The Gambia, may be caused by several factors, including some related to the local vectors, whose contribution is poorly understood.METHODSUsing WHO susceptibility bioassays, insecticide resistance status was determined in vector populations sampled from six pairs of villages across The Gambia, each pair contained a low and high prevalence village.RESULTSThree vector species were observed (23.5 % Anopheles arabiensis, 31.2 % Anopheles gambiae, 43.3 % Anopheles coluzzii and 2.0 % An. coluzzii × An. gambiae hybrids). Even at a fine scale, significant differences in species composition were detected within village pairs. Resistance to both DDT and deltamethrin was more common in An. gambiae, most markedly in the eastern part of The Gambia and partly attributable to differing frequencies of resistance mutations. The Vgsc-1014F target site mutation was strongly associated with both DDT (OR = 256.7, (95 % CI 48.6-6374.3, p < 0.001) and deltamethrin survival (OR = 9.14, (95 % CI 4.24-21.4, p < 0.001). A second target site mutation, Vgsc-1575Y, which co-occurs with Vgsc-1014F, and a metabolic marker of resistance, Gste2-114T, conferred additional survival benefits to both insecticides. DDT resistance occurred significantly more frequently in villages with high malaria prevalence (p = 0.025) though this did not apply to deltamethrin resistance.CONCLUSIONWhilst causality of relationships requires further investigation, variation in vector species and insecticide resistance in The Gambia is associated with malaria endemicity; with a notably higher prevalence of infection and insecticide resistance in the east of the country. In areas with heterogeneous malaria transmission, the role of the vector should be investigated to guide malaria control interventions.
AB - BACKGROUNDMalaria hotspots, areas with consistently higher than average transmission, may become increasingly common as malaria declines. This phenomenon, currently observed in The Gambia, may be caused by several factors, including some related to the local vectors, whose contribution is poorly understood.METHODSUsing WHO susceptibility bioassays, insecticide resistance status was determined in vector populations sampled from six pairs of villages across The Gambia, each pair contained a low and high prevalence village.RESULTSThree vector species were observed (23.5 % Anopheles arabiensis, 31.2 % Anopheles gambiae, 43.3 % Anopheles coluzzii and 2.0 % An. coluzzii × An. gambiae hybrids). Even at a fine scale, significant differences in species composition were detected within village pairs. Resistance to both DDT and deltamethrin was more common in An. gambiae, most markedly in the eastern part of The Gambia and partly attributable to differing frequencies of resistance mutations. The Vgsc-1014F target site mutation was strongly associated with both DDT (OR = 256.7, (95 % CI 48.6-6374.3, p < 0.001) and deltamethrin survival (OR = 9.14, (95 % CI 4.24-21.4, p < 0.001). A second target site mutation, Vgsc-1575Y, which co-occurs with Vgsc-1014F, and a metabolic marker of resistance, Gste2-114T, conferred additional survival benefits to both insecticides. DDT resistance occurred significantly more frequently in villages with high malaria prevalence (p = 0.025) though this did not apply to deltamethrin resistance.CONCLUSIONWhilst causality of relationships requires further investigation, variation in vector species and insecticide resistance in The Gambia is associated with malaria endemicity; with a notably higher prevalence of infection and insecticide resistance in the east of the country. In areas with heterogeneous malaria transmission, the role of the vector should be investigated to guide malaria control interventions.
U2 - 10.1186/s12936-016-1203-z
DO - 10.1186/s12936-016-1203-z
M3 - Article
SN - 1475-2875
VL - 15
JO - Malaria Journal
JF - Malaria Journal
IS - 1
M1 - 166
ER -
