Characterization of spontaneous gross and histologic findings in free-ranging Egyptian rousettes (Rousettus aegyptiacus) from Uganda with a review of reported pathogens

The emergence of significant viral pathogens and their escalating threats to human and animal health have intensified scientific interest in bats as disease vectors and natural reservoir hosts. Among chiropteran species, the Egyptian rousette (Rousettus aegyptiacus) assumes particular epidemiological significance as the established natural reservoir for orthomarburgviruses, encompassing the two recognized members Marburg virus and Ravn virus. While contemporary research predominantly emphasizes the detection and characterization of specific zoonotic agents within these populations, fundamental knowledge regarding their baseline pathology and the comprehensive impacts of disease on morbidity remains limited. Pathological investigations of free-ranging bat populations face inherent methodological constraints, frequently hampered by insufficient sample sizes or selection bias toward compromised specimens (e.g., moribund or deceased animals). This study addresses these limitations through comprehensive post-mortem examination and histologic evaluation of 69 free-ranging Egyptian rousettes from Uganda. These specimens were procured during systematic efforts to identify filoviral reservoir hosts, thereby providing an unprecedented opportunity to investigate spontaneous disease processes within an ostensibly healthy, representative population. Gross pathological examination identified lesions in 85.5% (59/69) of specimens, including scarring and fibrosis of the plagiopatagium and dactylopatagium (85.5%; 59/69), focal fibrotic nodules (17.4%; 12/69), and lacerations (17.4%; 12/69) within wing membranes. Histopathological analysis demonstrated the universal presence of microscopic alterations (100%; 69/69), with a cumulative total of 794 discrete lesions documented across 28 organ systems. The liver emerged as the most frequently affected organ, along with multiorgan perivascular cellular aggregates (both 81.2%; 56/69). This investigation represents the first comprehensive characterization of naturally occurring pathological processes in free-ranging Egyptian rousettes from Uganda. Elucidating the intrinsic factors that modulate reservoir species health is fundamental to understanding zoonotic disease spillover dynamics and developing evidence-based strategies for mitigating future outbreak risks in human and susceptible animal populations.