Leishmaniasis in deployed military populations: A systematic review and meta-analysis

Leishmaniasis affects military personnel deployed to endemic areas following exposure to sand flies infected with the protozoa Leishmania. This systematic review and meta-analysis of data specific to military populations aims to identify knowledge gaps to mitigate sand fly exposure and Leishmania transmission during deployments. The review was registered on PROSPERO (CRD42023463687). Random-effects meta-analyses and narrative synthesis were performed. Thirty-six studies were included, most of which reported on cutaneous leishmaniasis (CL), showing a mean cumulative incidence of 10% (95% CI: 5–16), suggesting higher rates in the Eastern Mediterranean region (14% [95% CI: 12–16]) compared to the African region (8%) and American region (9%). Asymptomatic Leishmania infection had a cumulative incidence of 11% (95% CI: 6–17), with higher rates in Eastern Mediterranean countries (20% [95% CI: 14–25]). Diagnosis involved parasitological, serological, and molecular methods, with L. (L) mexicana and L. (V.) braziliensis identified as the predominant CL pathogens in deployed troops in the Americas. Visceral leishmaniasis cases were less frequent, all reported from the Eastern Mediterranean and associated with the Leishmania donovani/infantum complex; whereas CL cases in the Old World were due predominantly to L. major and L. tropica. Regular use of long-lasting insecticidal nets to mitigate sand fly exposure demonstrated high potential effectiveness than other reported personal protective measures (PPMs) which yielded mixed or inconclusive results. In summary, the systematic review revealed the substantial variability between study designs and statistical integrity. There is need for more consistent and robustly designed studies including well-define controls and replication. Future studies would be advised to explore the long-term effectiveness and practicality of PPMs, both individually and in combination, across diverse deployment settings.Author summary: Leishmaniasis is a parasitic disease transmitted by sand flies that affects populations worldwide, with particularly increasing incidence among military personnel deployed to endemic regions. This systematic review and meta-analysis focuses on leishmaniasis among military populations, examining rates of infection, regional variations, and the effectiveness of preventive measures. Our study synthesises data from thirty-six studies, revealing a 10% overall incidence of cutaneous leishmaniasis (CL) among deployed troops, with the highest rates found in the Eastern Mediterranean region. Additionally, asymptomatic infections were observed at a cumulative rate of 11%, with significant regional variations. The review identifies L. (L) mexicana and L. (V.) braziliensis as the primary CL pathogens in the Americas, while L. major and L. tropica were the most common in the Eastern Mediterranean. The analysis also highlights the effectiveness of long-lasting insecticidal nets in reducing sand fly exposure, though other personal protective measures (PPMs) showed mixed results. Despite these findings, our study notes substantial variability in study design and statistical rigor across the included research, highlighting the need for more standardised, well-controlled studies with reproducible methodologies. This study provides recommendations for future research on leishmaniasis in military settings and beyond, advocating for long-term evaluations of PPM efficacy across diverse regions. The findings emphasise the importance of region-specific disease control strategies and add to the growing body of evidence guiding prevention, treatment, and policy in the neglected tropical disease community.