I think the most reliable way to analyze the viability of Leishmania in macrophages is to use IF microscopy. There is a nice publication about such an in vitro assay for drug discovery against Leishmania donovani, which includes infection of THP-1 macrophages with GFP-expressing Leishmania following analysis by IF microscopy. I hope this will help you.
Tegazzini D, Díaz R, Aguilar F, et al.
A Replicative In Vitro Assay for Drug Discovery against Leishmania donovani. Antimicrob Agents Chemother. 2016;60(6):3524-3532.