Visceral leishmaniasis in the Indian subcontinent: Optimizing the surveillance system for the post-elimination phase

Visceral leishmaniasis (VL) is a parasitic infectious disease transmitted by sand flies and fatal if not treated timely. It is targeted for elimination as a public health problem in the Indian subcontinent (ISC). The overarching aim of this thesis is to explore how the surveillance system for VL should be optimized towards the post-elimination phase in the ISC. Chapter 1 provides a general overview of leishmaniasis, before redirecting the focus to VL in the Indian subcontinent. We describe the clinical picture of both VL and its cutaneous sequel called post-kala-azar dermal leishmaniasis (PKDL), the diagnostic and treatment modalities, and current disease control and surveillance activities. We discuss how in the early 2000s, India, Nepal and Bangladesh together accounted for 70% of all global cases, with an estimated 160 to 320 thousand new VL cases each year in the ISC, and how this resulted in a regional initiative to eliminate VL as a public health problem, defined as an annual incidence < 1/10,000 population in all endemic (sub-)districts, with a deadline originally set at 2015 but currently revised to 2026. We summarize the progress made to date, and how Bangladesh was the first country to be certified for elimination of VL as a public health problem in 2023. In addition, we illustrate how close India and Nepal are to reaching this goal as well, and describe which key challenges still threaten a sustainable elimination in the long run. These include incomplete coverage of the surveillance system, limitations of the available tools, and waning of political commitment in a post-elimination phase as the most important ones. The research in this thesis addresses the following three research questions: 1) How has the epidemiology of VL changed since the start of the elimination initiative in the Indian subcontinent? 2) To what extent do specific infectious subgroups require an additional focus for VL surveillance? 3) What indicators should be monitored in the post-elimination phase?