3. Recommendations on malaria vector control
3.2 VECTOR CONTROL ACROSS DIFFERENT MALARIA TRANSMISSION SETTINGS
3.2 VECTOR CONTROL ACROSS DIFFERENT
MALARIA VECTOR CONTROL GUIDELINES
In areas10 with ongoing local malaria transmission (irrespective of both the pre-intervention and the current level of transmission), the scale-back of vector control should not be undertaken. Universal coverage with effective malaria vector control of all persons in such areas should be pursued and maintained.
Good practice statement
In areas where transmission has been interrupted, the scale-back of vector control should be based on a detailed analysis that includes assessment of the receptivity and vulnerability, active disease surveillance system, and capacity for case management and vector control response.
Good practice statement
Access to effective vector control interventions will need to be maintained in the majority of countries and locations where malaria control has been effective. This includes settings with ongoing malaria transmission, as well as those in which transmission has been interrupted but in which some level of receptivity and vulnerability remains. Malaria elimination is defined as the interruption of local transmission (reduction to zero incidence of indigenous cases) of a specified malaria parasite species in a defined geographical area as a result of deliberate intervention activities.
Following elimination, continued measures to prevent re-establishment of transmission are usually required (24). Interventions are no longer required once eradication has been achieved. Malaria eradication is defined as the permanent reduction to zero of the worldwide incidence of infection caused by all human malaria parasite species as a result of deliberate activities.
A comprehensive review of historical evidence and mathematical
simulation modelling undertaken for WHO in 2015 indicated that the scale- back of malaria vector control was associated with a high probability of malaria resurgence, including for most scenarios in areas where malaria transmission was very low or had been interrupted. Both the historical review and the simulation modelling clearly indicated that the risk of resurgence was significantly greater at higher EIRs and case importation rates, and lower coverage of active case detection and case management (26).
10 The minimum size of an area is determined by the availability of reliable disaggregated disease surveillance data and feasibility for decisions on vector control implementation. The area is not necessarily based on administrative boundaries.
During the pre-elimination and elimination phases, ensuring universal access to vector control for at-risk populations remains a priority, even though the size and specific identity of the at-risk populations may change as malaria transmission is reduced.
As malaria incidence falls and elimination is approached, increasing heterogeneity in transmission will result in foci with ongoing transmission in which vector control should be enhanced. Such foci may be due to particularly intense vectorial capacity, lapsed prevention and treatment services, changes in vectors or parasites that make the current strategies less effective, or reintroduction of malaria parasites by the movement of infected people or, more rarely, infected mosquitoes. Guidance on entomological surveillance across the continuum from control to elimination is provided elsewhere (23).
Once elimination has been achieved, vector control may need to be continued by targeting defined at-risk populations to prevent reintroduction or resumption of local transmission.
It is acknowledged that malaria transmission can persist following the implementation of a widely effective malaria programme. The sources and risks of ‘residual transmission’ may vary by location, time and the existing components of the current ‘effective malaria programme’. This variation is potentially due to a combination of both mosquito and human behaviours, such as when people live in or visit forest areas or do not sleep in protected houses, or when local mosquito vector species bite and/or rest outdoors and thereby avoid contact with IRS or ITN/LLIN.
Supplementary interventions such as larval source management (LSM) can be used in addition to the core interventions in specific settings and circumstances. Recommendations on larviciding with chemical or biological insecticides are outlined in a subsequent chapter. The VCAG on new tools, technologies and approaches is currently evaluating a number of new interventions that have the potential to address residual transmission (http://www.who.int/vector-control/vcag/). Implementation of supplementary interventions should be in accordance with the principles outlined in the Global vector control response 2017–2030 (6).
Once elimination has been achieved, vector control coverage should be maintained in receptive areas where there is a substantial risk for reintroduction (i.e. vulnerable areas).
MALARIA VECTOR CONTROL GUIDELINES
SUPPLEMENTARY INTERVENTIONS
Once high coverage with a core intervention has been achieved, recommended supplementary interventions with proven public health value may be deployed as a public health intervention in specific settings and circumstances. The decision to deploy a supplementary vector control intervention should only be taken after conducting a prioritization analysis across malaria interventions, not just vector control, to ensure maximum impact of any additional resources.
Good practice statement
There is a critical need for all countries with ongoing malaria transmission, and in particular those approaching elimination, to build and maintain strong capacity in disease and entomological surveillance and health systems. The capacity to detect and respond to possible resurgences with appropriate vector control relies on having the necessary entomological information (i.e. susceptibility status of vectors to insecticides, as well as their biting and resting preferences). Such capacity is also required for the detailed assessment of malariogenic potential that is a pre-condition for determining whether vector control can be scaled back (or focalized).