Q fever in the Irish dairy herd

INTRODUCTION: Coxiella burnetii, the causative agent of Q fever, is a notifiable zoonotic pathogen in Ireland. While typically subclinical in ruminants, infection is associated with reproductive losses. In humans, disease can range from asymptomatic to more serious complications. Ruminants have been identified as the main reservoir for human infection. Ireland’s dairy cattle industry has expanded substantially in recent years, yet current data on the national prevalence of Coxiella burnetii in dairy herds are limited. Understanding the herd-level prevalence and associated risk factors is essential for informing disease management and control strategies. METHODS: Bulk milk tank testing results from an Irish dairy cooperative herd health programme were analysed to determine the apparent and true prevalence of Coxiella burnetii antibodies, using 2022 data. Further analysis was conducted to determine the relationship between Coxiella burnetii prevalence and co-morbid disease and herd characteristics. RESULTS: 2687 dairy herds were included in the sample. The true prevalence of Coxiella burnetii antibodies was 61.7%. Coxiella burnetii prevalence was associated with increasing herd size, whereas higher herd average EBI and lower replacement rates were associated with decreased odds of infection. CONCLUSION: This study provides updated data, revealing the highest herd-level prevalence of Coxiella burnetii antibodies reported to date in Ireland. The association with larger herd size is particularly relevant with the substantial growth in the national dairy herd over the past decade. These findings reinforce the need for further research into transmission dynamics, impact on production and zoonotic risk.