Malaria has been one of the major public health problems in Sub-Saharan African countries and Guinea Bissau is no exception. Thanks to the universal distribution of insecticide-impregnated mosquito nets, funded by the Global Fund, malaria prevalence in Guinea Bissau decreased by over 90% since 2011. Other malaria preventive, diagnostic and treatment contributed to this reduction. However, the country is still affected by the disease, which is mainly transmitted by Anopheles Gambiae mosquitoes. Monitoring every 2 years mosquito sensitivity and resistance to insecticides used in nets are an integral part of malaria control actions with our partner the Bandim Health Project and the Portuguese National Institute of Health – Vector Research Center.

Field Work: Between 29 September and 18 October 2021, researchers from the above institution collected samples from 5 regions namely, Bafata, Bissau, Buba, Cacheu and Gabu, to assess the susceptibility of mosquitos to insecticides using World Health Organisation provided kits.

Laboratory work: Mosquitoes were exposed to different insecticides: Pyrethroids (Permethrin, Deltamethrin, Cyfluthrin), Organochlorines (DDT dichloro-diphenyl-trichoethane 4%), Organophosphates (Fenitrothion 1%), PBO (piperonyl butoxide (4%).

Results: The preliminary result showed that mosquitoes in Guinea Bissau are resistant to major categories of insecticides. Fortunately, mosquitoes were sensitive to 1 type of insecticide (PBO) in 4 of the 5 regions above 95% efficacy. Concerning is the very high resistance of An. gambiae to permethrin + PBO in the health region of Bafatá as shown in the graph. 

Implication: Based upon previous studies which indicated mosquito resistance to insecticides, the country with GF support has changed the types of nets being used for preventive services. These nets are however more expensive than nets with traditional insecticides, limiting funds for other malaria control activities.