Visceral leishmaniasis (VL) is now an emerging disease in Sri Lanka (Siriwardana et al., 2017; Manokaran et al., 2017; Tilakaratne et al., 2018; Jayasekera et al., 2018). Although majority of local cases still represent cutaneous form of the disease (Siriwardana et al., 2010, Siriwardana et al., 2019a; Samaranayake et al., 2016; Galgamuwa et al., 2018), visceralizing potential of initially skin localizing strains cannot be completely excluded due to virulent nature of the causative parasite, Leishmania donovani (Siriwardana et al., 2018; Deepachandi et al., 2020b). Therefore, early disease confirmation is very important to prevent death from this fatal disease (Siriwardana et al., 2017).

Parasitological (i.e., light microscopy and in vitro culturing) and molecular diagnostic methods (i.e., PCR) are currently used for diagnosis of VL in local settings (Ihalamulla et al., 2008; Lachaud et al., 2002; Deepachandi et al., 2019). Also an enzyme-linked immunosorbent assay (ELISA) based serological assay has been recently developed and validated for local VL detection which is important as a second line assay (Deepachandi et al., 2023). However parasitological techniques are more useful in determining current and on-going infection.

In vitro cultivation of Leishmania is also essential in different other purposes including production of antigens and antibodies, assessment of parasite immune modulating capabilities, drug screening, improvements in chemotherapy, differentiation of clinical isolates, determination of strain differences, vaccine production, development of attenuated strains and for continued supplying of viable organisms for studying host-parasite interactions (Afrin et al., 2002; Mukhopadhyay et al., 2012; Deepachandi et al., 2020a). Prevention of contaminations from other organisms (i.e., bacterial and fungi) is challenging in isolation of parasites in vitro.

Due to complex life-cycle and existence of different morphological stages of Leishmania within sandfly vector and the host, some Leishmania culture protocols are still undefined for in vitro conditions (Gossage et al., 2003). This is mainly due to the requirement of different culture parameters that depend on different life cycle stages. These Leishmania life cycle stages involve number of variables including the parasitic form, host site, host temperature, host immune response, parasite species and/or strain and parasite-protective mechanisms which directly or indirectly affect for their ability to grow under in vitro conditions (Visvesvara and Garcia, 2002; Gossage et al., 2003; Dostálová and Volf, 2012; Ahmed, 2014). It will be extremely demanding if an in vitro culture system can imitate the vector or host environment by supplying all the relevant variables. This requires more time, knowledge about different culture conditions for growing different Leishmania strains, different culturing techniques and different culturing media or other supplements/conditions. Also Leishmania parasites may be difficult to grow depending on the species or strains and may require media components that may be still undefined. In some occasions, different growth factors substituted for serum supplements have been reported. In this complex nature of culturing Leishmania parasites in vitro, more research are compulsory to the development of defined media (Visvesvara and Garcia, 2002; Gossage et al., 2003; Dostálová and Volf, 2012; Ahmed, 2014; Li et al., 2017).

Aim of this study was to evaluate in vitro growth ability of Leishmania parasites causing visceral infections in Sri Lanka and to compare the same with dermotropic variants to identify their differences associated with in vitro growth characteristics.