Transmission Dynamics of Torque Teno Sus Virus 1 (TTSuV1) Between Wild and Farmed Pigs: A Molecular Tool for Monitoring Cross-Population Spillover in Swine.

Torque teno sus virus 1 (TTSuV1) is a ubiquitous, non-pathogenic virus in both wild and domestic pigs and has potential value as a molecular marker for monitoring cross-population viral transmission and biosecurity breaches. In this study, we integrated genetic data with Bayesian transmission inference to examine the dynamics of TTSuV1 transmission within and between wild and farmed pigs in Arkansas. Transmission steps, defined as the number of transmission events linking two hosts, were used to identify barriers to transmission, such as biosecurity measures or geographic separation. TTSuV1 was highly prevalent in farmed pigs (96.59%) and invasive wild pigs (47.76%), with sequences from both groups distributed across four major subtypes. Transmission step analyses revealed that wild-farmed pig pairs were consistently separated by numerous transmission steps (>10 steps), indicating strong isolation and little evidence of recent spillover. In contrast, few transmission steps (≤5 steps) were common within populations, reflecting localized circulation. Our findings support the use of TTSuV1 as a molecular marker to characterize cross-population viral movement and spillover, as well as to delineate population structure in swine systems. Practically, this approach offers a novel framework for using viral genomics to detect cross-population spillover events and monitor biosecurity breaches in swine production systems.