Koala retrovirus dynamics in the Snowy Monaro, NSW

Abstract

Koala Retrovirus (KoRV) is in transition from exogenous virus to endogenous element and shows distinct profiles between northern and southern koala populations. Northern animals carry high proviral copy numbers of endogenous KoRV-A and a range of exogenous subtypes, while southern koalas instead generally only possess degraded and recombinant versions of the virus. In this study we investigated the KoRV profiles of koalas in the Snowy Monaro (SM) region of southern NSW, which is at the intersection between northern and southern populations. We found that SM koalas have lower KoRV loads and proviral copy numbers than koalas from other northern populations. Plasma RNA subtype profiles were very consistent between individuals with all animals having KoRV-A at low relative abundance and high proportions of subtypes D and L. This pattern of subtype profiles is unique compared to other populations studied and suggests that KoRV-D and/or L may be endogenous in southern NSW or that KoRV-A is effectively suppressed in koalas from the region. Despite these unique profiles, in agreement with findings from other regions, higher KoRV loads were associated with C. pecorum shedding. Further, KoRV loads were temporally stable with no consistent changes found over time in koalas in the wild or koalas rescued from burnt habitat after fire and brought in for rehabilitation. Further studies into the role KoRV plays in disease susceptibility in southern NSW and into the endogenization status of KoRV-D/L will provide important insights into this model of retroviral endogenization and guide koala conservation efforts in the region.