Increasing outdoor host-seeking in Anopheles gambiae over 6 years of vector control on Bioko Island.
BACKGROUND
Vector control through indoor residual spraying (IRS) has been employed on Bioko Island, Equatorial Guinea, under the Bioko Island Malaria Control Project (BIMCP) since 2004. This study analyses the change in mosquito abundance, species composition and outdoor host-seeking proportions from 2009 to 2014, after 11 years of vector control on Bioko Island.


METHODS
All-night indoor and outdoor human landing catches were performed monthly in the Bioko Island villages of Mongola, Arena Blanca, Biabia and Balboa from 2009 to 2014. Collected mosquitoes were morphologically identified and a subset of Anopheles gambiae sensu lato (s.l.) were later identified molecularly to their sibling species. Mosquito collection rates, species composition and indoor/outdoor host-seeking sites were analysed using generalized linear mixed models to assess changes in mosquito abundance and behaviour.


RESULTS
The overall mosquito collection rate declined in each of the four Bioko Island villages. Anopheles coluzzii and Anopheles melas comprised the An. gambiae s.l. mosquito vector population, with a range of species proportions across the four villages. The proportion of outdoor host-seeking An. gambiae s.l. mosquitoes increased significantly in all four villages with an average increase of 58.8 % [57.9, 59.64 %] in 2009 to 70.0 % [67.8, 72.0 %] in 2014. Outdoor host-seeking rates did not increase in the month after an IRS spray round compared to the month before, suggesting that insecticide repellency has little impact on host-seeking behaviour.


CONCLUSIONS
While vector control on Bioko Island has succeeded in substantial reduction in overall vector biting rates, populations of An. coluzzii and An. melas persist. Host-seeking behaviour has changed in these An. gambiae s.l. populations, with a shift towards outdoor host-seeking. During this study period, the proportion of host-seeking An. gambiae s.l. caught outdoors observed on Bioko Island increased to high levels, exceeding 80 % in some locations. It is possible that there may be a genetic basis underlying this large shift in host-seeking behaviour, in which case outdoor feeding could pose a serious threat to current vector control programmes. Currently, the BIMCP is preparing for this potential challenge by testing source reduction as a complementary control effort that also targets outdoor transmission.
Department of Entomology, Texas A&M University, College Station, TX, USA. jacob.i.meyers@gmail.com.
Jacob I
JI
Meyers
Department of Entomology, Texas A&M University, College Station, TX, USA.
Sharmila
S
Pathikonda
Department of Entomology, Texas A&M University, College Station, TX, USA.
Zachary R
ZR
Popkin-Hall
Department of Entomology, Texas A&M University, College Station, TX, USA.
Matthew C
MC
Medeiros
Medical Care Development International, Malabo, Equatorial Guinea.
Godwin
G
Fuseini
Medical Care Development International, Malabo, Equatorial Guinea.
Abrahan
A
Matias
Medical Care Development International, Malabo, Equatorial Guinea.|MRC Tropical Epidemiology Group, London School of Hygiene and Tropical Medicine, London, UK.
Guillermo
G
Garcia
Department of Mathematical Sciences and Technology, Norwegian University of Life Sciences, Ås, Norway.|Institut de Recherche Pour Le Développement (IRD), MIVEGEC, Montpellier, France.|Department of Entomology, Faculty of Agriculture, Kasetsart University, Bangkok, Thailand.
Hans J
HJ
Overgaard
Department of Entomology, Texas A&M University, College Station, TX, USA.
Vani
V
Kulkarni
Department of Entomology, Texas A&M University, College Station, TX, USA.
Vamsi P
VP
Reddy
Medical Care Development International, Silver Spring, MD, USA.
Christopher
C
Schwabe
MRC Tropical Epidemiology Group, London School of Hygiene and Tropical Medicine, London, UK.
Jo
J
Lines
MRC Tropical Epidemiology Group, London School of Hygiene and Tropical Medicine, London, UK.|School of Pathology, Faculty of Health Sciences, University of Witwatersrand, Johannesburg, South Africa.
Immo
I
Kleinschmidt
Department of Entomology, Texas A&M University, College Station, TX, USA.
Michel A
MA
Slotman
D000818:Animals; D000852:Anopheles / Q000187:drug effects / Q000502:physiology*; D044822:Biodiversity; D016703:Equatorial Guinea; D005247:Feeding Behavior; D007306:Insecticides / Q000494:pharmacology; D009032:Mosquito Control; D000072138:Mosquito Vectors / Q000502:physiology*; D011157:Population Dynamics
D007306:Insecticides
Anopheles coluzzii; Anopheles gambiae; Anopheles melas; Bioko Island; Bioko Island Malaria Control Project; Equatorial Guinea; Indoor residual spraying; Outdoor host-seeking; Vector control