Understanding the transmission dynamics of Leishmania donovani to provide robust evidence for interventions to eliminate visceral leishmaniasis in Bihar, India

Abstract

Visceral Leishmaniasis (VL) is a neglected vector-borne disease. In India, it is transmitted to humans by Leishmania donovani-infected Phlebotomus argentipes sand flies. In 2005, VL was targeted for elimination by the governments of India, Nepal and Bangladesh by 2015. The elimination strategy consists of rapid case detection, treatment of VL cases and vector control using indoor residual spraying (IRS). However, to achieve sustained elimination of VL, an appropriate post elimination surveillance programme should be designed, and crucial knowledge gaps in vector bionomics, human infection and transmission need to be addressed. This review examines the outstanding knowledge gaps, specifically in the context of Bihar State, India.The knowledge gaps in vector bionomics that will be of immediate benefit to current control operations include better estimates of human biting rates and natural infection rates of P. argentipes, with L. donovani, and how these vary spatially, temporally and in response to IRS. The relative importance of indoor and outdoor transmission, and how P. argentipes disperse, are also unknown. With respect to human transmission it is important to use a range of diagnostic tools to distinguish individuals in endemic communities into those who: 1) are to going to progress to clinical VL, 2) are immune/refractory to infection and 3) have had past exposure to sand flies.It is crucial to keep in mind that close to elimination, and post-elimination, VL cases will become infrequent, so it is vital to define what the surveillance programme should target and how it should be designed to prevent resurgence. Therefore, a better understanding of the transmission dynamics of VL, in particular of how rates of infection in humans and sand flies vary as functions of each other, is required to guide VL elimination efforts and ensure sustained elimination in the Indian subcontinent. By collecting contemporary entomological and human data in the same geographical locations, more precise epidemiological models can be produced. The suite of data collected can also be used to inform the national programme if supplementary vector control tools, in addition to IRS, are required to address the issues of people sleeping outside.

The yin and yang of leishmaniasis control

“…One of the most visible is a collaborative effort towards elimination of visceral leishmaniasis (VL) as a public health problem in the Indian sub-continent through a multidisciplinary and integrative approach ranging from case detection and treatment to vector control [3, 17, 18]. The WHO in partnership with member states (India, Bangladesh and Nepal), the Bill & Melinda Gates Foundation, Drugs for Neglected Diseases initiative , the KalaCORE Consortium among others have committed resources, expertize and funds to eliminate VL - defined as a reduction in the annual incidence of VL to <1 per 10 , 000 cases per endemic block - in the Indian subcontinent by 2020 [18].…”

Longitudinal Study of Transmission in Households with Visceral Leishmaniasis, Asymptomatic Infections and PKDL in Highly Endemic Villages in Bihar, India

“…Understanding the relative contributions of L . donovani transmission by individuals with PKDL and asymptomatic infections is crucial for designing control and elimination strategies [13, 14]. To address these issues, a longitudinal study was undertaken to follow family members from households with asymptomatic and PKDL cases alongside households with VL cases.…”

Patchy Parasitized Skin Governs Leishmania donovani Transmission to Sand Flies

“…One of the burning questions facing programs aimed at control and elimination of anthroponotic visceral leishmaniasis (AVL) concerns identification of the main source of infection for sand fly vectors [1, 2]. To date, the comparative contribution of asymptomatic, symptomatic or post-kala azar dermal leishmaniasis patients to outward transmission of Leishmania donovani , the causative agent of AVL, to vector sand flies remains unknown and represents a serious obstacle to control efforts.…”