Coxielosis in dairy cattle herds: serological and molecular study

Abstract

Purpose: Ruminants are recognized as the main reservoirs of Coxiella burnetii. In Portugal, in 2014, in a survey in apparently healthy dairy cattle herds from the center region, 37.8% of herds evidenced an exposure to C. burnetii. Furthermore, milk shedding was demonstrated in 20% of these herds. The present study aimed: i) to investigate the exposure to C. burnetii in dairy cattle herds from the same region by testing BTM to the presence of specific anti-C. burnetii antibodies ii) to evaluate the milk shedding in exposed herds iii) to evaluate the degree of bacterial excretion in shedding herds; iv) compare results with those obtained in 2014(1). Methods & Materials: A cross-sectional study was carried out in dairy cattle herds (n=30) from central Portugal with no previous vaccination to Q fever. Bulk tank milk (BTM) samples were collected and tested by a commercial ELISA (ID Screen Q Fever Indirect Multispecies®, IDVet). Antibodies positive BTM samples were tested by qPCR (Taq-Vet™ Coxiella burnetii–Absolute Quantification, Thermofischer®) Results: A total of 5398 females with a mean age of 3.2 years (SD=0.73) from 30 herds were tested. An antibody positive result was obtained in 96.7% (95% CI: 83.3-99.4) of herds and S/P% ranged from 49 to 432. The shedding of C. burnetii in BTM was detected in 31.03% (95% IC: 17.27-49.23) and a high bacterial load (≥3 × 103 bacteria/mL) was observed in 44.4% of PCR positive BTM. Comparison of results from 2014 to 2021, shows that the exposure to C. burnetii increased significantly (p<0,0001). Conclusion: Serological and molecular methods in combination are a crucial tool for Coxielosis surveillance. From 2014 until 2021, an increase of the exposure as well as an increase of bacteria shedding in BTM was observed. It is recognized that the shedding of C. burnetii through milk is important, especially in dairy cattle, and thus the milk as a potential source of infection among dairy workers should not be neglected.