Although considerable progress has been made in malaria control in Cambodia over the past decade, the disease remains a major concern for the international community, the Ministry of Health, and the Cambodian people. This is primarily due to the confirmed spread of resistance to artemisinin drugs, the principal component of the first-line malaria treatments that are currently used worldwide. In Cambodia, PMI supports malaria elimination activities, procurement of antimalarial commodities based on identified gaps, surveillance for antimalarial drug resistance, and insecticide resistance and vector monitoring activities.
The Malaria Elimination Action Framework (MEAF) (2016-2020) aims to interrupt transmission of P. falciparum in areas of multidrug resistance, including ACT resistance, by no later than 2020 (MEAF, 2016). In Cambodia, malaria transmission is endemic in 21 out of 25 provinces, but incidence is highest in the north eastern part of the country, where the malaria burden has become more concentrated over the past three years. Malaria risk is highest in forest or forest fringe areas of the country, generally along the borders of Vietnam, Lao People’s Democratic Republic, and Thailand.
Malaria transmission in Cambodia is rapidly changing and is closely associated with two major malaria vectors that inhabit the forest and forest fringe, Anopheles dirus and An. minimus. An. dirus is found in forested mountains and foothills, cultivated forests, and rubber plantations, whereas An. minimus is found outside the forests or in areas where the forests have been cleared. Twenty five malaria vector species have been identified in Cambodia between 2007 and 2013. Other vectors such as An. barbirostris, An. phillipinensis, An. vagus, and An. hyrcanus are also present in Cambodia. These vectors bite during all hours of the evening, but peak biting hours are usually found to be outdoors between 8 pm and 12 am. St. Laurent et al. (2016) demonstrated that cow baited traps are effective in sampling diverse Anopheles malaria vectors at high numbers and should be considered in parallel with human-baited traps.
The MEAF 2016-2020 calls for development of a vector management strategy and strengthening of entomological surveillance for malaria elimination, including routine insecticide resistance monitoring.
In line with MEAF, under other projects, PMI had (a) previously supported training of one CNM staff member on use of World Health Organization (WHO) susceptibility test kits and Centers for Disease Control and Prevention (CDC) bottle bioassays for detecting insecticide resistance, (b) identified entomological monitoring as a priority to assist in targeting vector control interventions, and (c) provided technical assistance and developed a plan for entomological surveillance as part of foci investigation in malaria elimination areas. Foci investigations, including entomological monitoring, are being implemented in Pursat, Pailin, and Battambang as part of the PMI-Cambodia Malaria Elimination Project (CMEP).
Building on this initial work, VectorLink Cambodia will work with CNM, provincial health departments (PHDs), operational districts (ODs), and the Laboratory of Malaria and Vector Research, U.S. National Institute of Allergy and Infectious Diseases (NIAID) to conduct entomological monitoring in 2020-2021. The project’s primary objective is to support entomological surveillance that focuses on higher burden geographical areas (in consultation with CNM) with an emphasis on improved insecticide resistance monitoring in coordination with other projects and routine vector surveillance. The project will also develop capacity through training to implement entomological surveillance and insecticide resistance monitoring.
Insectary and Laboratory Activities:
- Rear F1 wild collected malaria vectors from forced oviposition at the CNM insectary for subsequent insecticide susceptibility tests.
- Maintain and expand the existing pinned reference collection of Anopheles
- Work with CNM to label mosquito samples for storage and recording prior to in-country ELISA.
- Conduct circumsporozoite protein (CSP) ELISA at the NIAID laboratory at CNM.
- Send specimens to U.S. Centers for Disease Control and Prevention (CDC) in Atlanta for molecular species identification of enzyme-linked immunosorbent assay (ELISA) positive samples and a sub-set of ELISA negative samples.
- Establish new sentinel sites (one forest and one village in forest fringe) for vector surveillance in each of the two sentinel provinces through training, provision of equipment, and close supervision by the CNM central-level technicians and VectorLink Cambodia technicians.
- Conduct monthly monitoring of malaria vector bionomics using human double net traps (HDNs), CDC light traps (CDC LTs), Furvela tent traps (FTTs), and cow-baited double net traps (CDNs).
- Conduct pyrethroid insecticide resistance testing in two sites (one forest and one village) per province for a total of four sites.
- Convene and support CNM to hold national Vector Control Working Group meetings.
- Facilitate review of entomological monitoring data by relevant parties to inform and improve integrated vector control decision making at the VectorLink Annual Dissemination and Planning Meeting as well as CNM-convened meetings (e.g., CNM Annual Conference and Technical Workshop and other malaria stakeholder meetings).
- Train and support the CNM technicians in mosquito trapping methods, handling and processing of mosquito samples in the field, morphological identification, insecticide resistance testing, CSP ELISA (in NIAID at CNM), data recording, entry and management, and reporting.
- Train and support CNM leadership on reporting and using vector control data for decision-making at the national level. Support CNM leadership to prepare and present mosquito surveillance data at technical working group meetings.
 Integration of entomological data into the CNM management information system will occur in Year 4. In Year 3, VectorLink Cambodia will share the data in an Excel sheet.