The Dynamic Transmission of Simbu Group Viruses in New South Wales, Australia.

Arthropod-borne orthobunyaviruses belonging to the Simbu serogroup can cause congenital and neurological disease in livestock. Across Australia, the National Arbovirus Monitoring Program (NAMP) conducts surveillance for veterinary-important arboviruses. Our study complements this broader surveillance framework by investigating the virus-specific transmission patterns of Simbu group viruses (SGVs) present in New South Wales (NSW). To describe the distribution of six SGVs: Akabane, Aino, Douglas, Peaton, Tinaroo, and a recently recognised Shamonda-like virus, we examined 24 years of serological data (2000-2023) from NSW sentinel cattle. The transmission of a Simbu serogroup virus was detected during every monitoring period (October-July), progressing from north to south along the NSW coastline. Inland transmission west of the Great Dividing Range (GDR) was intermittent (2012-2013, 2020, and 2022), when SGV distribution extended across the mountain range or progressed down the western slopes from Queensland. From 2014, repeated seasonal SGV transmission extended to the far south coast of NSW. Peaton virus was the most frequently detected and widely distributed virus. Since testing for the newly detected Shamonda-like virus started in 2019, this virus has been widely detected across coastal NSW and often in herds also infected with Douglas or Peaton viruses. Discrepancies between the ELISA and virus neutralisation test (VNT) results suggest that this virus could have been present in NSW as early as 2012. From 2017, Akabane virus has a sporadic distribution. The distribution for both Aino and Tinaroo viruses was sporadic (2005-2023). These findings highlight the importance of long-term, virus-specific surveillance in identifying emerging variants and detecting exotic incursions.