Eswatini has made major investments in improving malaria control and surveillance, including significant policy changes enabling the NMP to rapidly respond to cases. Despite all the efforts to make Eswatini malaria-free by 2020, there has been little change over the past decade and the overall elimination strategy has fallen short of its target. Eswatini has managed to keep malaria controlled with relatively low annual incidence rates compared to its neighbor Mozambique and other E-2020 countries in the region [1, 18]. However, outbreaks could still not be prevented within the case study’s observation period. The reviewed data suggest that higher case numbers are associated with decreased vector control efforts. This is especially well illustrated in 2017 when hardly any structures were sprayed, and local malaria transmission increased rapidly, reaching an unprecedented high over the study observation period. Whilst an excellent surveillance system has been established in the country, and investigation rates have improved over the years, there still remains around a fifth of the reported cases that are uninvestigated, an area which must be improved if elimination is to be achieved. Reviewing the NMP databases highlighted significant missing demographic data (GPS coordinates, case origin data) which limited the mapping of malaria cases and IRS coverage. This missing information is pertinent for a country that is aiming for elimination, as all cases need to be identified and mapped for proper and effective deployment of vector control interventions .
IRS remains one of the most powerful vector control interventions for reducing/interrupting malaria transmission in terms of its immediate impact. Its use in the last seven decades has played a major role in the elimination of malaria from southern Europe, the Mediterranean region, Russia, large parts of Asia and Latin America, as well as many parts of South Africa . In Eswatini, IRS is supposed to be implemented annually in October, marking one spray cycle before the start of the major local malaria season. This strategy aims to target the local cases that seem to peak later in the year as observed in this case study. In 2016, the IRS effort was reduced and targeted at the few local transmission hotspots observed in the previous year when IRS was more widely applied. In 2017 hardly any IRS was done. This reduced vector control effort correlated with major outbreaks of local cases in an expanded area of lowveld and lower middleveld regions. The exploration of the data suggests that IRS applications were frequently targeted in areas seen to be persistent malaria hotspots in the previous year. However, this targeted approach might have not considered that the higher coverage with IRS in the previous year prevented most of the cases that would have been seen without intervention. The increase of the IRS efforts in 2018 was associated with reductions in malaria incidence.
The mapped locations receiving IRS from the data provided by the NMP surveillance, highlights significant gaps in strategic deployment of this vector control tool to targeted malaria hotspots in some of the studied period (years). Studies have shown IRS to be an effective strategy for preventing malaria infection and mortality across a range of transmission settings [21–26]. However, low coverage and poor quality of IRS can limit the impact on malaria transmission . The reasons of Eswatini’s low coverage in 2017 was attributed to challenges in the procurement of insecticide, hence only limited amounts of insecticide (lambda-cyhalothrin) that remained from the previous season was used and targeted at outbreaks rather than prior transmission season hotspots. In 2018, IRS coverage maps show much more spraying. However the challenges in procurement extended to 2018 and hence whilst there was increased coverage, the timing of IRS was not adhered to and was done late in many targeted regions . In summary, challenges experienced by the NMP due to procurement and resource allocation led to poor planning and execution of IRS which led to insufficient coverage. Since IRS is at the core of Eswatini’s vector control strategy, this delay had major impact on malaria control. To get on track with the elimination effort, it is necessary for the NMP to clearly identify and address the challenges in the implementation of IRS in order to sustain vector control.
Many factors have been shown to contribute to malaria outbreaks in various settings in Eswatini including, rainfall, temperature, population movement, and the lack of sufficient or appropriate control tools or timings of vector control strategies . Control of malaria transmission in border areas, together with the importation of cases, presents a major threat to successfully eliminating malaria in Eswatini. Population movement, especially from the malaria-endemic neighbouring Mozambique, have been previously recorded as an important factor contributing to persistence of malaria cases in Eswatini . The reviewed data supported these international border movements contributing to malaria cases
Eswatini can be described as low transmission and high importation case, similar to what is described in a study in Ethiopia where the local transmission risk was apparently very low, but many cases likely originated from other countries . The high numbers of imported cases that were observed in this Eswatini study during the first few months of the year are likely caused by workers from Mozambique returning to Eswatini in January following the Christmas and New Year holidays . Additionally, high case importation rates have been credited to sugar plantation workers whose travel patterns are well known between Eswatini and Mozambique . Currently, Eswatini’s NMP carry out malaria screening at the Eswatini/Mozambique border where they do not treat the positive cases but rather refer them to a nearest health facility. The data in this study clearly indicates the outbreaks are due to local transmission, which calls for two different responses: for cases imported to areas where transmission is unlikely, it is more a medical treatment case, so border check and treatment; whilst for local cases there needs to be more emphasis on vector control. Elsewhere it has been previously demonstrated in Eastern Myanmar that early diagnosis and prompt onsite treatment of confirmed cases is effective in achieving malaria elimination (14). In addition, it has been observed in southern Iran, that the presence of foreign immigrants could cause malaria outbreaks (15). Therefore, there is need for Eswatini to strengthen its cross-border surveillance, form collaborations with its neighbouring countries and learn from past lessons such as the cross-border initiative Lubombo Spatial Development Initiative (LSDI) . This initiative represented collaborative efforts between Eswatini, Mozambique and South Africa to reduce each country’s malaria importation risk and achieve elimination. LSDI led to success towards malaria elimination in both South Africa and Eswatini, with IRS as the core intervention [6, 7]. However, the termination of LSDI resulted in an upsurge of malaria cases in these countries, mainly as a result of migration from high transmission areas to low transmission ones . The LSDI focus on vector control with IRS, further demonstrates the importance role of vector control in elimination efforts, and in particular, IRS.
This case study has programmatic implications. IRS has in the past successfully proven to work in Eswatini to manage cross-border transmission via the LSDI regional malaria control collaboration  and has for over 70 years contributed to eliminating malaria from various countries when integrated with other measures . Integrated vector management (IVM) is the rational decision-making process to maximize the impact of resources allocated for vector control for long-term sustainability . It might be timely for Eswatini to consider an integrated approach for malaria control adding tools such as long-lasting insecticidal nets (LLINs) , screening of house entry points  and targeted larviciding  along with chemoprophylaxis in their malaria control toolbox. Operational research should support such efforts towards IVM  which has been demonstrated in other countries including Zambia , and Tanzania [37, 38]. In Zambia, the interventions include IRS, LLINs, larviciding and environmental management implemented in eligible urban and rural areas . In Tanzania, integrated control of urban mosquitoes in Dar es Salaam using community sanitation supplemented by larviciding was successful in managing mosquitoes [37, 38].
Furthermore, there is need to improve the entomological surveillance in Eswatini to clearly identify and monitor malaria vectors. Despite the country’s emphasis on vector control, surprisingly little is known about the local vector species and population dynamics, the role of secondary vectors in malaria transmission and the status of insecticide resistance. Equally, implementation of resistance management strategies and alternative approaches including natural-based interventions will be pivotal for effective IVM and attainment of the objectives of the Stockholm Convention . A review of procedures and challenges at programme level might help to improve vector control implementation including routine entomological surveillance in sentinel sites in the different ecological zones. Overall, the review of the malaria control effort over the past 8 years highlights the need to invest in strengthening human resources and infrastructural capacity. These include training and retaining of personnel with the necessary skills, laboratories, an insectary, establish systems for timely procurement, appropriate storage, and adherence to standard operating procedures.