Decoding silent hosts: perspectives on asymptomatic Leishmania carriage dynamics

Leishmaniasis, a neglected tropical disease caused by protozoan parasites of the genus Leishmania, constitutes a spectrum of diseases ranging from asymptomatic cases to symptomatic visceral and integumentary (cutaneous and mucous membranes) leishmaniasis. Asymptomatic carriers are suspected to represent a major hidden reservoir in endemic regions, which constitutes a main challenge for the control and potential elimination of the disease. This review discusses current knowledge on the immune dynamics, diagnostic challenges and transcriptomic signatures associated with asymptomatic Leishmania infection and immune dynamics of symptomatic cases, concentrating on the visceral and cutaneous forms of the disease. Understanding the molecular and immune processes behind asymptomatic carriage is essential for the strategies to be taken at many levels: therapy, transmission, as well as control. We show further that transcriptomics, proteomics and other advanced approaches represent powerful tools to identify and compare differential gene expression, immune pathways, and metabolic changes in symptomatic and asymptomatic cases. ONE SENTENCE SUMMARY: Asymptomatic infections constitute a major underestimated hidden reservoir for Leishmania infections in endemic regions ("silent host"), a main challenge for the control and potential elimination of the disease.