In Liberia, PMI implemented the Africa Indoor Residual Spraying (AIRS) project to control malaria from 2009 to 2013. Insecticide resistance monitoring during this time indicated that Anopheles gambiae s.l., the major vector of malaria in Liberia, is resistant to the pyrethroid class of insecticides. In 2013, after presenting empirical evidence on vector resistance to pyrethroids and evidence of susceptibility to pirimiphos-methyl, the National Malaria Control Program (NMCP) and IRS Task Force switched from using pyrethroids to pirimiphos-methyl for IRS in 2013. This was the final year in which IRS was implemented in Liberia.

After the withdrawal of IRS in 2014, PMI and NMCP continued entomological monitoring to generate data on vector bionomics including species composition, distribution, and behavior. In addition, a container insectary was established on the NMCP compound for rearing Anopheles gambiae for insecticide susceptibility tests and to perform morphological species identification of field-collected mosquitoes.

Following the end of the PMI AIRS project, entomological monitoring activities transitioned to the PMI VectorLink Project in 2017 with routine monitoring being conducted in three sites – Frank Town (Montserrado County), a peri-urban area; Tomato Camp (Bong County), a rural highland area; and Jeneta (Margibi County), a rural zone. To better understand the dynamics of malaria vectors in areas outside the sentinel sites, VectorLink also began sampling mosquitoes in 10 sites along a transect from Yekepa, Nimba County in the North to Careysburg, Montserrado County, in the South. Mosquitoes were collected in May 2017, October 2017, and May 2018. The final collection planned initially for October 2018 will not be implemented following the decision to expand the number of fixed sentinel sites.

PMI VectorLink has worked in close collaboration with the NMCP and Liberian Institute of Biomedical Research (LIBR) to build local capacity for laboratory analysis of mosquito samples. Currently, laboratory analyses are being conducted by NMCP and LIBR staff at LIBR facilities. Following training in 2018, staff began conducting enzyme-linked immunosorbent assays (ELISAs) to determine sporozoite infection rates among mosquitoes collected in 2015 and beyond.

During its third year, the project will work with NMCP, NPHIL, LIBR, and the University of Liberia, as well as county and district staff, to conduct routine monthly vector bionomics monitoring, insecticide resistance, and implementation of ITN activities. The project’s primary objective is to provide technical assistance to support vector control activities, including support of entomological surveillance and ITN activities, which will guide further malaria vector control interventions.

Insectary and Laboratory Activities

  • Support the NMCP to manage the insectary, maintain the mosquito colony, and ensure that all activities in the insectary follow standard protocols;
  • Build national and local capacity in laboratory analyses of mosquito samples through on-site training and supervision;
  • Finish renovating the LIBR laboratory, including replacement or provision of essential laboratory equipment, to enable in-country molecular analyses of entomological samples to include analyses for mosquito species identification, Plasmodium falciparum sporozoite rate, and identification of molecular markers for insecticide resistance and blood-meal source.

Field Activities

  • Conduct insecticide susceptibility testing in seven sites across seven counties, prioritizing those insecticides that are found on ITNs, which is the main vector control intervention in Liberia. This will include pyrethroids (deltamethrin, permethrin) with and without pre-exposure to the synergist PBO, alpha-cypermethrin, and chlorfenapyr. Resistance intensity assays will be conducted where applicable.
  • Conduct monthly vector bionomics monitoring in four routine sites to monitor the spatial and temporal distributions and densities of Anopheles vector species, and characterize their biting and resting behavior.
  • Train local staff in entomological monitoring activities.

ITN Activities

  • Support ITN durability monitoring data collection at the 24-month time point.
  • Develop a protocol for entomological and epidemiological data collection to monitor the effectiveness of large-scale distribution of Interceptor G2 ITNs in the 2021 mass campaign.
  • Collect baseline data to monitor the impact of G2 ITN mass distribution in 2021, including collection of entomological data and insecticide resistance data in four select sites.

National-Level Support

  • Support the NMCP to implement a National Insecticide Resistance Management Plan;
  • Coordinate and participate in quarterly national vector control working group meetings which include the review of entomological monitoring data by relevant parties to inform and improve integrated vector control decision-making;
  • Train and supervise the NMCP technicians and University of Liberia staff in entomological techniques of malaria vectors and provide on-the-job training and coaching of these staff at sentinel sites;
  • Support transfer of skills to national level stakeholders for data management and analysis, managing the insectary, and entomological monitoring.

Success stories from PMI VectorLink Liberia

Forging Partnerships for Progress in Malaria Prevention