Antigen-specific antibody responses following tuberculin administration in clinically healthy camelids

Serological assays are used alongside tuberculin skin testing to improve detection of bovine tuberculosis (bTB) in camelids. Tuberculin-induced anamnestic antibody responses have been described in infected animals; however, the effect of single and repeated tuberculin exposure on antigen-specific antibody responses in clinically healthy, tuberculosis-free camelids has not been evaluated. A retrospective observational study was undertaken involving alpacas and llamas subjected to voluntary or regulatory tuberculin administration, including single or repeated injections within 12 months before serological testing using the Camelid Enferplex multiplex ELISA. Animals were clinically healthy and originated from herds with no credible suspicion or history of bTB before or after testing. An unprimed control cohort from a biosecure, tuberculosis-free herd was included for comparison. Serological reactors underwent statutory post-mortem examination. Camelids exposed to tuberculin demonstrated consistent antibody reactivity to a defined subset of antigens, in the assay-reported order: MPB70-derived peptide (MPB70pep), bovine purified protein derivative (PPDB), MPB83, CFP-10 and MPB70. This pattern occurred in clinically healthy animals with no epidemiological risk factors or clinical, pathological or bacteriological evidence of Mycobacterium bovis infection at post-mortem examination. Nevertheless, ten animals were classified as serological reactors and compulsorily removed under regulatory provisions. In contrast, unprimed control animals showed no persistent multi-antigen antibody reactivity. Tuberculin administration alone, including repeated exposure within 12 months, can induce patterned antibody responses detectable by the Camelid Enferplex assay independent of infection. In low-prevalence spillover species, such responses may have important regulatory and welfare consequences, highlighting the need to consider tuberculin exposure history, herd biosecurity, herd disease status and species-specific immunology when interpreting serological results.