Genetic Analysis of Leishmania donovani Tropism Using a Naturally Attenuated Cutaneous Strain

Abstract

A central question in Leishmania research is why most species cause cutaneous infections but others cause fatal visceral disease. Interestingly, L. donovani causes both visceral and cutaneous leishmaniasis in Sri Lanka. L. donovani clinical isolates were therefore obtained from cutaneous leishmaniasis (CL-SL) and visceral leishmaniasis (VL-SL) patients from Sri Lanka. The CL-SL isolate was severely attenuated compared to the VL-SL isolate for survival in visceral organs in BALB/c mice. Genomic and transcriptomic analysis argue that gene deletions or pseudogenes specific to CL-SL are not responsible for the difference in disease tropism and that single nucleotide polymorphisms (SNPs) and/or gene copy number variations play a major role in altered pathology. This is illustrated through the observations within showing that a decreased copy number of the A2 gene family and a mutation in the ras-like RagC GTPase enzyme in the mTOR pathway contribute to the attenuation of the CL-SL strain in visceral infection. Overall, this research provides a unique perspective on genetic differences associated with diverse pathologies caused by Leishmania infection.

Author Summary

Visceral leishmaniasis is one of the most lethal parasitic diseases, and the mechanisms that govern its survival in visceral organs are not understood. Here, we obtained an atypical cutaneous Leishmania donovani clinical isolate from Sri Lanka and compared it to a typical visceral disease causing clinical isolate. Through whole genome sequencing, bioinformatics analysis, experimental infection in mice and functional genomic analysis, this study provides novel information on what differentiates a deadly visceral strain from a benign cutaneous strain. Results indicate that the ability of Leishmania parasites to cause visceral or cutaneous leishmaniasis may be determined by mutations or amplification of a few genes, or combinations of these factors. Overall, this work contributes to the understanding of parasite virulence and may help guide disease control efforts.