Timing of seroconversion and acquisition of positive polymerase chain reaction assay results in calves experimentally infected with bovine leukemia virus

OBJECTIVE: To determine the interval to provirus and serum antibody detection (via PCR assay and ELISA, respectively) in calves after experimental inoculation with bovine leukemia virus (BLV). ANIMALS: 8 colostrum-deprived, BLV-negative Holstein bull calves (> or = 6 weeks old). PROCEDURES: Via IM injection, each calf received a fresh whole-blood inoculum (day 0) calculated to contain 2 x 10(6) lymphocytes. Blood samples for the ELISA and PCR assay were collected from calves immediately prior to inoculation and weekly thereafter for 7 weeks. Mean and median number of weeks to PCR-detected conversion of BLV status and seroconversion were calculated. Point sensitivity and cumulative sensitivity of the 2 assays were calculated at each sample collection. At each sampling time, the proportion of calves identified as infected by the cumulative weekly ELISA and PCR assay results was compared by use of a Fisher exact test. RESULTS: In 5 calves, conversion of BLV status was detected via PCR assay before seroconversion was identified. However, seroconversion preceded PCR-detected conversion in 2 calves. In 1 calf, both assays yielded positive results at the same test date. These differences were not significant. CONCLUSIONS AND CLINICAL RELEVANCE: In experimentally inoculated BLV-negative calves, conversion of BLV status was detected via PCR assay more quickly than via ELISA; this difference was not significant and probably not clinically important. The PCR assay may be useful as a confirmatory test in animals of exceptional value; tests based on viral identification may become critically important if vaccines against BLV infection are developed and marketed.