Summary
This investigation of a Q fever abortion cluster on a Uruguayan dairy farm found that whilst 22.5% of cows at parturition were seropositive for C. burnetii, all newborn calves tested at birth were seronegative, suggesting congenital transmission is not a major route of infection in this herd. Critically, 95% of seronegative calves seroconverted to IgG-positive within 24 hours of ingesting imported commercial colostrum replacer, a finding with important implications for interpreting seroprevalence surveys in herds using such products.
Regional applicability
The findings are relevant to UK dairy producers and veterinary diagnosticians using colostrum replacers, particularly imported products, as passive transfer of maternal antibodies from replacement colostrum could be misinterpreted as evidence of active infection or herd exposure in serological surveys. Similar risk may apply to other zoonotic pathogens present in colostrum replacer sources.
Key measures
Anti-C. burnetii IgG seropositivity (ELISA); C. burnetii DNA detection (PCR); timing of seroconversion relative to colostrum replacer ingestion
Outcomes reported
The study determined the seroprevalence of C. burnetii in a dairy herd experiencing Q fever abortions, identified whether live-born calves were congenitally infected, and demonstrated that seronegative newborn calves seroconverted after ingesting imported commercial colostrum replacer. Serological and PCR testing were used to assess infection status in cows and calves.
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