Monitoring Pathogens in Free-Living Large Herbivores in a Nature Reserve in the Netherlands

Monitoring and surveillance of pathogens are crucial for safeguarding animal and public health. While passive surveillance is more common for wild and free-living animals, active monitoring improves the detection and characterisation of specific pathogens relevant to animal and public health. In the Oostvaardersplassen (OVP) nature reserve in the Netherlands, an active monitoring system for Heck cattle (Bos taurus), Konik horses (Equus caballus) and red deer (Cervus elaphus) has been in place since 1997. This study utilised the data generated from the monitoring system to estimate pathogen prevalence and to evaluate the ongoing monitoring efforts. Yearly prevalences were calculated for each observed pathogen, and probability of freedom from infection was assessed for pathogens that were not detected. In cattle, the highest antibody prevalences (>35%–50%) were observed for Bovine herpesvirus 1 (BoHV-1), Bluetongue virus (BTV), Schmallenberg virus (SBV) and Fasciola hepatica, whereas lower (<25%) prevalences were detected for Bovine viral diarrhoea virus (BVDV), Coxiella burnetii, Mycobacterium avium subsp. paratuberculosis (MAP), Salmonella spp. and S. Dublin. Similar pathogens were observed in red deer and cattle, but prevalences were generally lower in red deer. In horses, Equine herpesvirus 1 and 4 (EHV-1 and 4), Salmonella spp., S. Dublin and S. Typhimurium were detected. Bovine leukaemia virus (BLV), Brucella abortus, Mycobacterium bovis (bTB) and Leptospira interrogans serovar Hardjo were not detected in cattle and red deer, nor were Equine infectious anaemia virus (EIAV), Equine influenza virus (EIV) and West Nile virus (WNV) observed in horses. Most of the detected pathogens are endemic in the Netherlands, while non-detected pathogens often have an official disease-free status. This study provides valuable insights into pathogen presence in free-living large herbivores at the OVP nature reserve. The current monitoring system is highly valuable and its effectiveness can be further enhanced through improvements, such as increased sampling efforts and pathogen prioritisation. This knowledge could guide the implementation of similar monitoring strategies in nature reserves across Europe.