The "piroplasmosis-like" syndrome in cattle on Réunion Island: Spatial and temporal distribution of cases and clinical impact of co-infections.

This study reports the results of a survey of bovine clinical cases of 'piroplasmosis-like' syndrome (PLS) on Réunion Island, encompassing haemoparasitoses such as anaplasmosis (Anaplasma marginale) and babesiosis (Babesia bovis, B. bigemina), as well as orbiviroses, notably epizootic haemorrhagic disease (EHD) and bluetongue (BT). A total of 170 cattle displaying PLS symptoms were sampled between February 2024 and August 2025 and were tested for multiple pathogens using RT-qPCR. Co-infections were common, affecting 67% of cattle. In particular, co-infection with A. marginale and B. bovis was associated with increased clinical severity compared to A. marginale infection alone, with a mortality rate of 50% versus 33% for all sampled cattle. Spatial distribution revealed that PLS clinical cases were sampled only in the western and southern parts of the island. Significant disparities in infection rates were detected across the covered climatic zones, with the Central high-altitude plain exhibiting the highest incidence (12.8 cases per 1000 cattle). Temporal variations showed a clear seasonal pattern, with most cases occurring during the southern hemisphere summer (November to April). Sporadic cases of orbiviroses were detected during the studied period.