Impact of sequelae of visceral leishmaniasis and their contribution to ongoing transmission of Leishmania donovani

Abstract

Visceral leishmaniasis (VL) in the Old World is caused by infection with Leishmania donovani. Although the numbers of new reported cases of VL in Africa have been relatively stable for several years, the low numbers currently reported on the Indian subcontinent suggest a positive impact of new treatments and intervention strategies. In both regions, however, VL relapse and post-kala-azar dermal leishmaniasis (PKDL) maintain infectious reservoirs and therefore present a threat to control programs. In this review, we outline the evolving appreciation of PKDL as an impactful disease in its own right and discuss the various diagnostic methods that can be applied for the detection and characterization of PKDL cases. We also highlight the data that indicate the potential, and likely contribution, of PKDL cases to ongoing transmission of L. donovani.

Keywords: Leishmania; biomarkers; diagnosis; protozoa.

Figure 1.

Worldwide distribution of VL in 2015. The WHO regional distribution of VL cases reported to WHO in 2015 is plotted (WHO 2017). Regions that report autochthonous PKDL are shown in color, while those that do not are shown in white. ¹By WHO reporting structure, Somalia and Sudan are considered to be within the Eastern Mediterranean Region. Three eco-epidemiological hotspots emerge in the region of East Africa (Ethiopia, Kenya, Somalia, South Sudan, Sudan and Uganda)¹, the Indian subcontinent (Bangladesh, India and Nepal) and Brazil.

Figure 2.

Transmission cycle of Leishmania donovani parasite in anthroponotic VL complications and magnitude of their infectiouness to vector. A systematic depictation of transmission of the parasite to naïve individuals through biting of infectious sand fly; pathogenic progression of the disease from the asymptomatic state; the major organ/ tissue localization of L. donovani in diseased individuals; the parasite uptake (in percent) of sand flies investigated through xenodiagnosis; and the relative proportions of PKDL presentations in L. donovani-endemic regions. PKDL presents most commonly as a sequelae in treated VL patients but can, in a minority, be a primary manifestation of L. donovani infection. The uptake and transmission of L. donovani by sand flies can occur during blood meals on VL and PKDL patients, with asymptomatic infected individuals also likely contributing.

Figure 3.

Various presentations of PKDL. PKDL is collectively the manifestation of lesions or hypo-pigmented skin rashes and is characterized by papular, macular and/or nodular lesions over the body. Shown are nodular lesions on forearm and extensive macular lesions on forearms, abdomen and back. Images are the authors' own.