Coxiella burnetii seroconversion in neonatal calves in an infected dairy herd attributable to ingestion of imported colostrum replacer rather than vertical transmission

Abstract

In April–June 2017, a cluster of 4 third-trimester abortions caused by Coxiella burnetii was diagnosed on a dairy farm with 356 Holstein cows in Uruguay. We investigated 1) the seroprevalence of C. burnetii in cows delivering normal calves in this herd, 2) whether non-aborting cows gave birth to seropositive and/or PCR-positive newborn calves in the year of the abortion cluster, and 3) whether seronegative newborn calves seroconverted after ingesting colostrum replacer. In March–September 2017, serum samples were collected from 133 calving cows and their calves immediately after birth and before colostrum ingestion. All 266 sera were analyzed for anti–C. burnetii IgG by ELISA. Additionally, 179 blood samples from some of these animals (82 cows, 97 calves) were PCR-tested for C. burnetii DNA. Thirty of the 133 (22.5%) cows delivering normal calves were seropositive at parturition; 4 of 82 (4.9%) were PCR-positive. All calves tested at birth by ELISA and PCR were negative. Our results suggest that congenital infection is not an important route of C. burnetii transmission to live-born calves in this herd. We observed that 76 of 80 (95%) seronegative newborn calves in 2021 became seropositive for anti–C. burnetii IgG at 24-h-old after drinking an imported commercial colostrum replacer, which could confound seroepidemiologic surveys in herds using colostrum replacers.