Feasibility of eliminating visceral leishmaniasis from the Indian subcontinent: explorations with a set of deterministic age-structured transmission models

Abstract

BackgroundVisceral leishmaniasis (VL) is a neglected tropical disease transmitted by sandflies. On the Indian subcontinent (ISC), VL is targeted for elimination as a public health problem by 2017. In the context of VL, the elimination target is defined as an annual VL incidence of <1 per 10,000 capita at (sub-)district level. Interventions focus on vector control, surveillance and on diagnosing and treating VL cases. Many endemic areas have not yet achieved optimal control due to logistical, biological as well as technical challenges. We used mathematical modelling to quantify VL transmission dynamics and predict the feasibility of achieving the VL elimination target with current control strategies under varying assumptions about the reservoir of infection in humans.MethodsWe developed three deterministic age-structured transmission models with different main reservoirs of infection in humans: asymptomatic infections (model 1), reactivation of infection after initial infection (model 2), and post kala-azar dermal leishmaniasis (PKDL; model 3). For each model, we defined four sub-variants based on different assumptions about the duration of immunity and age-patterns in exposure to sandflies. All 12 model sub-variants were fitted to data from the KalaNet study in Bihar (India) and Nepal, and the best sub-variant was selected per model. Predictions were made for optimal and sub-optimal indoor residual spraying (IRS) effectiveness for three different levels of VL endemicity.ResultsStructurally different models explained the KalaNet data equally well. However, the predicted impact of IRS varied substantially between models, such that a conclusion about reaching the VL elimination targets for the ISC heavily depends on assumptions about the main reservoir of infection in humans: asymptomatic cases, recovered (immune) individuals that reactivate, or PKDL cases.ConclusionsAvailable data on the impact of IRS so far suggest one model is probably closest to reality (model 1). According to this model, elimination of VL (incidence of <1 per 10,000) by 2017 is only feasible in low and medium endemic settings with optimal IRS. In highly endemic settings and settings with sub-optimal IRS, additional interventions will be required.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-016-1292-0) contains supplementary material, which is available to authorized users.

Elimination of visceral leishmaniasis in the Indian subcontinent: a comparison of predictions from three transmission models

“…Note, however, that the dependence of the SHR on the IRS efficacy is linear in models E0 and E1, but exponential in model W (see Additional File 1 of (Le Rutte et al, 2016) and Supplementary File 1).…”

Prevalence of visceral leishmaniasis, risk factors and associated disorders: Knowledge of inhabitants and professionals in Fulbaria, Mymensingh

“…VL is the world's second-deadliest parasitic disease after malaria, with 400,000 cases and 40,000 deaths occurring annually (Alvar et al 2006). VL is a neglected tropical disease transmitted by sandflies (Le Rutte et al 2016). The disease burden is highest in India, followed by Bangladesh and Nepal.…”

Leishmaniasis: current challenges and prospects for elimination with special focus on the South Asian region

“…Post-kala azar dermal leishmaniasis (PKDL) is also an intriguing clinical scenario described in India and occurs in 5-10% of VL cases following apparent cure of VL (and sometimes with no history of preceding VL). PKDL patients presents with macular papular skin lesions and are speculated to act as reservoirs for VL transmission (due to the parasite-rich nature of the skin lesions) (Ready, 2014), although such significance of PKDL remains debatable (Le Rutte et al, 2016; Hirve et al, 2017). …”