First molecular phylogenetic and serological insights into Listeria monocytogenes infection in aborted ewes in Iraq: A cross-border comparative analysis

Background and Aim: Listeria monocytogenes is a significant zoonotic pathogen linked to reproductive losses in livestock and serious health risks in humans. In Iraq, listeriosis remains underreported in sheep, with limited data on its molecular and epidemiological characteristics. This study aimed to (1) estimate the seroprevalence of L. monocytogenes in recently aborted ewes, (2) evaluate the association between seropositivity and clinical indicators, and (3) perform molecular detection and phylogenetic analysis of polymerase chain reaction (PCR)-confirmed isolates. Materials and Methods: From November 2023 to August 2024, 168 aborted ewes in Wasit Province, Iraq, were sampled for vaginal swabs and blood. Enzyme-linked immunosorbent assay (ELISA) was used for serological screening, while DNA extracted from swabs underwent PCR amplification targeting the 16S ribosomal RNA gene. PCR-positive samples were sequenced and phylogenetically analyzed using MEGA-11 software. Clinical data were statistically correlated with seropositivity using odds ratios (OR) and relative risk (RR). Results: ELISA revealed a seroprevalence of 23.21%, with the majority of infections classified as mild. PCR confirmed L. monocytogenes in 3.57% of swabs. Seropositivity significantly correlated with vaginal discharge (30.08%, p = 0.0121), retained placenta, and recent abortion history. Higher infection risk was observed in ewes with no or single previous abortions (OR = 2.464; RR = 2.207) and in flocks with ≤10% abortion rates (OR = 3.729; RR = 2.731). Phylogenetic analysis of six local isolates (GenBank IDs PQ865989.1–PQ865994.1) revealed 96.43%–97.62% sequence identity with an Iranian reference strain (MT071644.1), suggesting regional transmission links. Conclusion: This study is the first to molecularly characterize ovine L. monocytogenes in Iraq, revealing both the prevalence of subclinical infection and cross-border phylogenetic relationships. The integration of serological and molecular diagnostics highlighted underrecognized infections and provided novel insights into the epidemiology of strains. Findings emphasize the need for broader regional surveillance, improved diagnostic protocols, and biosecurity measures in ovine reproductive health management. Keywords: ovine abortion, Listeria monocytogenes, enzyme-linked immunosorbent assay, polymerase chain reaction, phylogenetic analysis, Iraq, Iran, 16S ribosomal RNA.