Summary
This investigation of a C. burnetii abortion cluster in a Uruguayan Holstein dairy herd revealed that congenital transmission to live-born calves was not a major route of infection, with all calves testing seronegative at birth. Unexpectedly, 95% of seronegative neonatal calves seroconverted within 24 hours of ingesting an imported commercial colostrum replacer, suggesting contamination of the replacer product rather than natural vertical transmission. This finding has important implications for seroepidemiological surveillance in herds using colostrum replacers, as passive transfer of maternal antibodies from replacer contamination may be misinterpreted as evidence of herd infection.
UK applicability
UK dairy farms using imported colostrum replacers may face similar contamination risks with C. burnetii or other pathogens, with implications for disease surveillance and herd health monitoring. The findings underscore the importance of verifying the microbial safety of colostrum replacer products used in UK herds and considering product source as a confounding factor in seroprevalence surveys.
Key measures
C. burnetii anti-IgG seropositivity by ELISA; C. burnetii DNA detection by PCR; seroprevalence in cows at parturition (22.5%); PCR positivity in cows (4.9%); seroconversion rate in calves post-colostrum replacer ingestion (95%)
Outcomes reported
The study determined seroprevalence of C. burnetii in a dairy herd during an abortion cluster, assessed vertical transmission routes to live-born calves, and identified unexpected seroconversion in neonatal calves following colostrum replacer ingestion. Serological and PCR testing were used to distinguish maternal antibodies from active infection.
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