Investigation of Coxiella burnetii distribution in a Scottish dairy cattle herd with history of stillbirths

Abstract

Background: Coxiella burnetii is a bacterial pathogen that can cause abortion and reproductive disease in livestock. In the UK, C. burnetii affects many dairy cattle herds, although the infection dynamics are poorly understood. Our study was performed to investigate infection patterns within a dairy cattle herd in Scotland that had experienced stillbirths attributed to C. burnetii infection.

Methods: Different management groups within the affected herd were sampled. Serology and qPCR testing of vaginal swabs were performed to investigate infection status. Regression analyses were performed to evaluate associations between diagnostic results and variables describing calving status and farm site.

Results: C. burnetii infection was detected in all management groups within the herd. The highest seroprevalence was detected in pre-calving heifers (78.6%) and the highest bacterial loads were detected in post-calving animals.

Limitations: These data represent a sample from one farm and testing for a single pathogen shedding route, which limits the generalizability of our findings.

Conclusions: C. burnetii infection is widespread within this affected herd. Marked differences were observed between the management groups, which may be explained by variables including pregnancy stage or environmental factors. Further work is needed to understand the implications of these results for the wider UK dairy sector.

FIGURE 1

Seroprevalence of Coxiella burnetii exposure in different cattle management groups sampled at a single Scottish dairy farm in 2022. 95% confidence intervals are displayed for each bar. Number of observations per group is labelled above each bar. ADU‐MF, post‐calving cows (all parities) at the main farm; PBH, pre‐bulling heifers; PCH‐HU, pre‐calving heifers at the heifer rearing unit; PCH‐MF, pre‐calving heifers at the main farm.

FIGURE 2

Scatterplot of qPCR Ct results obtained for Coxiella burnetii detection in cattle management groups sampled at a single Scottish dairy farm in 2022. Point colour indicates calving status where red denotes pre‐calving and blue denotes post‐calving. The horizontal lines indicate the thresholds applied for result classifications for positive samples with Ct values 40 or less (solid line), and samples classed as high‐load positives with Ct values 27 or less (dotted line). Points plotted at Ct value of 45 are negative samples with no evidence of amplification after 40 qPCR cycles and are included for illustration only. ADU‐MF, post‐calving cows (all parities) at the main farm; PBH, pre‐bulling heifers; PCH‐HU, pre‐calving heifers at the heifer rearing unit; PCH‐MF, pre‐calving heifers at the main farm.