Malaria epidemiology in Suriname from 2000 to 2016: trends, opportunities and challenges for elimination

An estimated 216 million cases of malaria occurred worldwide in 2016 [1]. Malaria incidence and mortality have been decreasing on a global scale between 2000 and 2015. More than half of the malaria-endemic countries achieved reductions in new malaria cases of at least 75% [2]. Malaria-endemic countries on the American continent, having experienced significant decreases in number of cases, contribute only a fraction to the global malaria burden. Several of these countries are moving towards elimination [3, 4]. Suriname is part of the Guianas (Suriname, Guyana, French Guiana) and had the highest annual parasite incidence (API) and concentration of Plasmodium falciparum cases in the Americas in 2004 [3, 5]. It has reported a significant decline in the number of cases since then after successful implementation of prevention and control interventions [6–8]. Suriname is committed to the goal of eliminating malaria by 2020 [9] but faces important challenges, including the reception of imported cases from other endemic countries in the region [6], and ongoing malaria transmission in remote gold mining areas [10].

In 2015, the World Health Organization launched a Global Technical Strategy for malaria 2016–2030 [11]. The strategy focuses on improved access to diagnosis and treatment and turning malaria surveillance into a core intervention. Malaria surveillance has become essential to identify high-risk areas for malaria and to guide the implementation of risk-based prevention and control strategies in the American region [11–14]. This study aims to describe the malaria morbidity and mortality trends and the geographical distribution of malaria in Suriname, taking into account the most probable origin of infection, for the period 2000 to 2016. Secondly, it aims to assess the spatiotemporal trends of malaria diagnosed in the health system notification points using data from the Suriname surveillance programme from 2007 to 2016. The overall objective is to evaluate the evolution of the disease in the last 17 years as well as to identify challenges and guide future interventions in order to achieve elimination in the country. The space–time cluster analysis of notification points will help identify priority service points, and allow for determination of risk population characteristics in these service points. This in turn enables better-targeted investments and interventions.

The study shows that Suriname experienced a period of stable high malaria incidence from 2000 to 2005 (around 160 cases per 1000 habitants per year). This was followed by a 10-year period of a steep decline in malaria transmission, which for a large part, especially between 2005 and 2010, was the result of a decline in the stable village communities (8). Since 2011, Suriname has consistently reported low malaria parasite indexes (1.0 per 1000 habitants in 2006) and decreasing numbers of severe cases. Pregnant women, and children < 5 years old were no longer diagnosed with malaria. Plasmodium malariae disappeared and P. falciparum was almost eliminated. Over time mobile migrant gold miners became the priority risk populations.

The decline in malaria transmission in Suriname is clear progress towards malaria elimination. The success of malaria control in Suriname is thought to be linked to a number of interventions such as improved surveillance, prevention strategies and case management [7, 6]. Prevention strategies included the free distribution of long-lasting insecticide-impregnated bed nets to risk populations, combined with an intensive education and awareness building campaign. The mass distribution of nets actually took place in a time of climatic instability, the combination of which is thought to have severely impacted the mosquito population in known high malaria risk areas at that time [17].

Case management and surveillance were improved with the introduction of RDTs in 2003. ACDs were implemented in remote gold-mining areas, and border screening posts were created along the border with French Guiana. Furthermore, the so-called Malaria Service Deliverer (MSD) network, as an innovative approach proved successful in getting access to the new risk population, the mobile migrant populations in remote mining areas. It provided miners with low-threshold access to malaria services, and was instrumental in eliminating remaining remote malaria hot spots. The approach is currently being considered for the provision of other health services directed toward this specific, hard-to-reach, target population. The space–time analysis data show that with ACDs, the MSD network and the border screening posts clusters of high incidence were captured.

Case management was also improved with the change of P. falciparum treatment from quinine to ACT with a single dose of primaquine in 2004. In Suriname P. falciparum and P. falciparum/mixed infection were the cause of 89% of the total number of cases in 2004 [5]. ACT reduces gametocyte transmission to mosquitoes. Primaquine enforces this effect [20–22]. Similar to comparable situations in the region [3, 23], effective treatment of P. falciparum cases was followed by a steep decline in P. falciparum infections, resulting in P. vivax becoming relatively more important. Since the P. falciparum infections were mostly a problem for the Maroon populations along the Tapanahony River and the eastern border with French Guiana, the decline in Surinamese cases had a spill-over effect in French Guiana [24].

Malaria imported cases in Suriname experienced a relative increase over the same time period, from 5.4% (467 cases) of all notified cases in 2004, to 75.6% (266 cases in 2016. Imported cases are mainly Brazilian nationals travelling from French Guiana as the most probable point of infection. Clusters of cases by notification points varied over the time period (2007–2016); however, almost all clusters are located in the southern and northern border area between Suriname and French Guiana (Lawatabiki and Albina posts). Investing in border screening at known crossing-sites for miners was a sound decision to manage imported malaria. In addition there is clustering in the migrant clinic of the Malaria Programme in Paramaribo, which shows that it filled a need.

The Malaria Programme is currently responsible for the vast majority of the national screening effort and is intercepting both autochthonous and imported cases. The population serviced and cases identified in the central level clinic, the MSD network and during ACDs originate mostly from the migrant risk populations. The cluster analysis shows that the expansion of notification points at central level (migrant clinic) and along the Suriname-French Guiana border (MSD network) are important for targeting high-risk population and rapidly detecting imported malaria cases. The spatiotemporal analysis of the surveillance data provides insights into the involvement of cross-border moving populations in the Surinamese malaria transmission dynamics. It offers a case for continued investment in these critical components of the national malaria surveillance and management system.

The importance of the mobile cross-border moving populations and the role of miners in malaria transmission is recognized throughout the region [25, 26]. Malaria and other health challenges in migrant gold miners, however, are a largely unrecognized or neglected problem in French Guiana [27, 28]. As a result, the number of imported malaria cases from French Guiana in neighbouring countries far exceeds the number of French Guiana cases reported by French health authorities [24]. While in many countries the number of P. falciparum cases greatly reduced following the introduction of effective treatment, malaria in cases imported from French Guiana into Suriname is still mostly due to P. falciparum infections. This can likely be linked directly to the absence of diagnosis and treatment services in the illegal mining settings [29]. Not addressing this malaria reservoir in French Guiana raises the threat of drug resistance [30–32] and puts the population of the Guianas and Brazil at risk for new malaria outbreaks and re-introduction of malaria in areas where elimination has been achieved [17]. Monitoring of resistance to malaria treatment should be in place.

The present study provides a countrywide overview of the malaria situation in Suriname with robust data from both active and passive case detection. It is a first study to give insight into the spatial and temporal trends of the relative burden of autochthonous versus imported malaria cases. The use of geographical information systems and space–time geo-statistics is becoming increasingly important to guide interventions for malaria control programmes [33, 34, 13]. This analysis will contribute towards a better understanding of malaria dynamics in the country. It will also contribute to improve the multi-country regional collaboration to eliminate hot spots and to cost-effectively manage malaria cases among cross-border moving migrant populations.

There are several limitations in this study. Due to the presence of the Medical Mission in the stable communities and the provision of malaria services by the Malaria Programme along the border and in remote mining areas, free access to diagnosis and treatment is available in most areas. However, due to high travel costs and a low perception of health priority in the mining population, self-treatment is common [24, 35] and under-reporting will occur. This means that a part of malaria infections may be missed in the surveillance system. Particularly, it is known that passive case detection is subject to sub-notification due to limitations such as travelling costs [36]. Also the remoteness of the risk areas and the inherent characteristics of the MSD network (including a high turnover of MSDs) impact quality control and cross-checking of RDT results (despite continuous supervision and regular refreshment trainings) in that blood smears are sometime of insufficient quality or absent.

Reaching malaria elimination in Suriname in 2020 requires national ownership of the elimination goal and leadership in achieving this. It also requires the development of a strategy for migrant health care, which is currently not in place. In order to develop a migrant health strategy, further insights into the characteristics, size and health needs of this migrant population are needed. The MSD network provides a basis upon which to build better access to migrant populations. Integration of health services in the network may result in a more sustainable system of health provision to this population. In addition, actions could be taken to lower the threshold for migrants, as a result of language or other barriers, to other health service providers both in the interior and at the central level. For the management of the so-called ‘hidden reservoir’ of malaria in mobile migrant populations in French Guiana, regional involvement is indispensable. Some regional cooperation for malaria is already in place, specifically a tri-national, innovative, pilot project to self-diagnose and self-treat malaria among migrant gold miners active in French Guiana (Malakit) [37] but the results presented here indicate that a strong involvement and full commitment of all partners is required, as is being established elsewhere [4], especially in the light of recent increases in the number of malaria cases reported in the American Region, including Guyana, Venezuela and Brazil [38].

Suriname has been successful in reducing malaria to near-elimination level. This success came about following a coordinated and adaptive (innovative) response by the Ministry of Health under guidance of the National Malaria Board, and with the support and funds of national and international partners. It could serve as a learning experience for other countries in the region. An important lesson learned is that bringing the interventions, especially bed nets and diagnosis and treatment, to the population at risk is a key element to achieve successful prevention and control. Surveillance data are an important tool to guide the programme and establish risk-based interventions. Innovative approaches can be developed to implement surveillance and case management in challenging situations, as was done with the MSD network in remote mining areas.

The national goal of malaria elimination by 2020 in Suriname will be hard to achieve if the number of malaria imported cases remains high. Re-introduction of malaria is a serious threat. A regional approach and collaboration within the Guianas and Brazil is essential. The elimination goal should be a regional goal.