Abstract Herpesvirus infections are common and mostly asymptomatic in vertebrates, but can result in impaired reproduction. It is therefore important to understand infection patterns and associated risk factors, particularly the effects of different stressors. Here we use Mustelid gammaherpesvirus 1 (MusGHV-1) infection in European badgers ( Meles meles ) as a host-pathogen wildlife model to study the effects of a variety of demographic, social, physiological and environmental stressors on viral reactivation in the genital tract. We collected 251 genital swabs from 151 free-ranging individuals across 3 trapping seasons (spring, summer and autumn). We screened for MusGHV-1 using PCR and explored possible links between genital MusGHV-1 reactivation and stressors, and their interactions, using logistic regression. In adults, reactivation was more likely in males, especially those in poorer body condition during summer. In females, reactivation was more likely when living in social groups comprising a higher percentage of cubs, but counter to our predictions, recent lactation appeared not influential. In relation to age, reactivation was more common in individuals over 8 years old than among prime age adults, and among juveniles (&lt;2 years old), especially females and individuals in better body condition, likely due to early puberty. Environmentally, reactivation was more prevalent in summer when food abundance is typically low. Our results evidence age effects on MusGHV-1 reactivation; in juveniles MusGHV-1 shedding in the genital tract is likely related to primary infection, while in adults, genital MusGHV-1 reactivation from latency was associated with aging, social and/ or environmental stress. Importance The immuno-suppressive effects of elevated stress levels facilitate disease development, and can ultimately cause host extinction at the population level, especially where diseases are transmitted sexually. The impacts of stress on host-pathogen dynamics through disease, however, are still poorly understood outside the laboratory or captive environments. Our study provides rare evidence from a free-ranging wild mammal population that the infection dynamics of a common and sexually transmittable gammaherpesvirus are linked to demographic, social, physiological and environmental stress. We propose that the effects of stressors on STIs and viral reactivation are an important factor to be taken into account in conservation efforts when working with vulnerable wildlife populations.

Patterns ofMustelid gammaherpesvirus 1(MusGHV-1) genital reactivation linked to stressors in adult European badgers (Meles meles)