Q fever in the Irish dairy herd – summary of research paper by Corridan K., Wall P., McGrath G. et al. Ir Vet J (2026).

This study provides the strongest Irish evidence to date that Q fever exposure is widespread and under recognised in dairy herds, highlighting the value of bulk tank milk testing in understanding herd level risk.

Background

• Q fever is caused by Coxiella burnetii and is a notifiable zoonotic disease in Ireland.
• Infection in cattle may be associated with:
  Reduced fertility
  Abortions
  Reproductive inefficiency
• Cattle are recognised reservoirs for human infection, particularly for farmers, farm staff and vets

Why this study was done?

• Previous Irish prevalence data were limited and over 10 years old. The Irish dairy sector has changed substantially with larger herds, increased intensity and greater animal densities. Updated data were needed to assess:
  • Current herd level exposure
  • Herd factors associated with Q fever positivity

Apparent prevalence: 53.5%

• The proportion of herds that tested positive on ELISA

True herd level prevalence: 61.7%

• Adjusted to account for the test sensitivity (86%) and specificity (99%).
• Represents the most accurate estimate of how many herds have been exposed

Context of these findings

• Represents a three fold increase compared with earlier Irish estimates (~19.5%)
• Higher than reported EU cattle averages (~15%), noting that EU figures often include beef and dairy cattle and surveillance is largely passive in many countries
• Describes that Q fever exposure is common, widespread and under recognised

Herd level risk factors identified

• Exposure was more likely in larger herds
• Exposure was less likely in herds with:
  • A higher average Economic Breeding Index (EBI)
  • A higher proportion of first lactation (younger) animals
• Higher exposure in herds with an older age structure likely reflects cumulative lifetime exposure

Clinical interpretation

• Highlights the subclinical and under recognised nature of Q fever
• Herd level exposure may act as a background contributor to reproductive performance issues rather than a single identifiable disease outbreak

Zoonotic context

• The study specifically highlights occupational risk to farmers, vets and families
• Therefore, this reinforces Q fever as a One Health issue, not just a production disease
• Humans are infected mainly via inhalation of aerosolised material from birth fluids or
  contaminated dust