Abstract
BackgroundInexpensive and convenient diagnostic tests for use in clinical work and for the surveillance of infection with Mycoplasma bovis are in demand. The objective of this longitudinal field study was to gain knowledge about the dynamics of antibodies against M. bovis in sera from naturally exposed calves with and without different clinical signs, measured by two different ELISA tests.ResultsA total of 83 calves were subject to between one and five blood samples and clinical examinations using a standard protocol during five herd visits to each of four outbreak dairy herds. The blood samples were analysed for the presence of antibodies against M. bovis using the commercial IgG ELISA test BioX K302 (BioX) and an in-house indirect IgG ELISA test (MilA ELISA).Linear mixed models were used to describe and compare the antibody dynamics as measured by the two tests in relation to the disease status and age of the animals.The BioX ELISA response was below the recommended cut-off (37 ODC%) for the entire study period in many of the calves. The estimated mean ODC% increased slowly but did not reach the recommended individual animal cut-off in three of the four herds. The highest estimated ODC% was not reached until the calf was 110–130 days old. The MilA ELISA response rose above the recommended cut-off (135 antibody units (AU)) in almost all calves, and in two herds, the estimated mean was above the individual animal cut-off shortly after the birth of the calf. The highest estimated antibody concentration was reached when the calf was approximately 60 days old. Disease status of the calf was not significantly associated with the results of either test.ConclusionsWe conclude that the BioX ELISA cannot be recommended for use in calves below 3 months of age. The MilA ELISA was able to detect antibodies shortly after birth (i.e. from approximately 3 weeks of age and onwards) and is therefore a more sensitive test for M. bovis exposure in young calves. Neither ELISA seemed able to differentiate between calves with arthritis and/or otitis media, and respiratory disease.
Highlights
Inexpensive and convenient diagnostic tests for use in clinical work and for the surveillance of infection with Mycoplasma bovis are in demand
The BioX Bio K enzyme-linked immunosorbent assay (ELISA) test (BioX) ELISA response was below the recommended cut-off of 37 ODC% for the entire study period for 48 of the calves, above the cut-off for the entire study period for eight calves, and 27 changed status (Fig. 1)
Antibody dynamics measured by the BioX ELISA In general, very few calves seroconverted to values above the recommended cut-off of 37 ODC%, and the majority remained below the cut-off for the BioX ELISA for the entire study period, despite the fact that these calves either showed signs of M. bovis-associated disease or were housed with diseased calves during acute outbreaks of disease caused by M. bovis
Summary
Inexpensive and convenient diagnostic tests for use in clinical work and for the surveillance of infection with Mycoplasma bovis are in demand The objective of this longitudinal field study was to gain knowledge about the dynamics of antibodies against M. bovis in sera from naturally exposed calves with and without different clinical signs, measured by two different ELISA tests. The primary diagnostic tool used in calves is bacterial culture of body fluid samples [2], but this is too expensive and time-consuming for use in Petersen et al BMC Veterinary Research (2018) 14:258 tool This knowledge requires longitudinal studies of naturally exposed calves, involving repeated observations of clinical signs combined with samples being taken for laboratory testing. Calves vaccinated with an experimental aerosol vaccine against M. bovis at three to 4 weeks and five to 6 months of age appeared to have a detectable immunoglobulin G (IgG) response against M. bovis within 14 days, and the antibody concentrations in serum remained at a high level for at least 42 and 30 days, respectively [3]
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