![]() Estimates of the proportion of reported VL patients co-infected with HIV in Bihar state are between 2% and 7%, although in districts where reliable HIV screening was present up to 20% of adults diagnosed with VL were HIV positive ( Directorate National Vector Borne Disease Control Programme India, 2017 Akuffo et al., 2018). At the same time it carries the second highest number of new HIV infections in the country, and is one of the seven Indian states where reported AIDS related deaths continue to rise ( National AIDS Control Organization, India). In 2019, Bihar reported 77% of all VL cases in India ( National Vector Borne Disease Control Programme I). The state of Bihar is located in northern India and is characterized by a very dense population of approximately 120 million, of which over a third live below the poverty line ( The World Bank, 2016). We therefore investigated to what extent the presence of patients with PKDL or VL-HIV is associated with VL incidence at the village level in Bihar, India. We hypothesized that with the overall decrease in VL cases reported in the Indian subcontinent, PKDL and VL-HIV+ cases act as important reservoirs of Leishmania transmission. However, their exact contribution to transmission of VL has yet to be determined. With each new episode of VL becoming increasingly difficult to treat ( van Griensven et al., 2014), these patients are likely to remain infectious Leishmania reservoirs for prolonged periods of time. In addition, VL-HIV+ patients experience a lower therapeutic success rate for VL, experience greater drug related toxicity and relapse more frequently than patients not infected with HIV ( Alvar et al., 2008 Cota et al., 2011 Burza et al., 2014b). Diagnosing VL in HIV-co-infected patients also poses a major challenge, as VL symptoms are less typical and existing diagnostic tools less accurate ( Singh, 2014). ![]() A concomitant HIV infection increases the risk of developing active VL by between 100 and 2,320 times ( World Health Organization Lopez-Velez et al., 1998). HIV infection and leishmaniasis share an immunopathological pathway that enhances replication of both pathogens and accelerates the progression of both VL and HIV ( Tremblay et al., 1996 Alvar et al., 2008 Mock et al., 2012). VL patients co-infected with HIV have been shown to be highly infectious towards sand flies ( Molina et al., 2003). Data from other settings in the Indian subcontinent are limited, in part due to a lack of routine testing of HIV among VL patients ( Akuffo et al., 2018). In Bihar, the most endemic state for VL in India, an estimated 2%–7% of VL cases are co-infected with HIV ( Directorate National Vector Borne Disease Control Programme India, 2017 Mathur et al., 2006 Burza et al., 2014a), although this is most likely an underestimation of the true burden ( Akuffo et al., 2018). As such PKDL is considered a largely hidden but persistent reservoir of infection, and remains a major threat to the sustainability of the elimination initiative. Following the near elimination of VL from the Indian subcontinent in the 1970s, PKDL was suspected to have been the interepidemic reservoir responsible for triggering a new VL outbreak years after the last VL case had been reported in West Bengal ( Addy and Nandy, 1992). PKDL, however, is infectious towards the sand fly vector and, if left untreated, can remain symptomatic for several years ( Das et al., 2014 Garapati et al., 2018). Because patients with PKDL usually do not have any symptoms other than painless skin lesions, a minority of these patients actively seek medical care, while the condition is often misdiagnosed as leprosy or vitiligo ( Ramesh et al., 2015 Zijlstra et al., 2017). ![]() Post-kala-azar dermal leishmaniasis (PKDL) is a cutaneous sequel that follows VL in an estimated 5%–10% of treated cases in Asia, typically 1–3 years following completion of therapy ( Zijlstra et al., 2003 Zijlstra et al., 2017). However, with the regional incidence of VL decreasing, understanding the role of potentially highly infectious subgroups in maintaining refractory Leishmania transmission is becoming increasingly important. Fifteen years after a Memorandum of Understanding was signed by the governments of India, Nepal and Bangladesh committing to its elimination as a public health problem, the goal is on the verge of being achieved. ![]() tropica has been isolated from VL cases in this region ( Khanra et al., 2012 Thakur et al., 2018). in the Indian subcontinent, the vast majority of cases is caused by Leishmania donovani, although also L. Visceral Leishmaniasis (VL) - also called kala-azar (KA) - is a potentially fatal parasitic disease.
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