Mycoplasma bovis antibody dynamics in naturally exposed dairy calves according to two diagnostic tests

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.

Characterisation of the course of Mycoplasma bovis infection in naturally infected dairy herds

“…Studies on M. bovis in dairy herds have focused on herds experiencing outbreaks of clinical mastitis (Hazelton et al 2018;Petersen et al 2018). In our study, the majority of the farms were infected, but had very few clinical cases, and could be therefore be defined as infected farms that were not experiencing an outbreak.…”

“…Therefore, the BioX ELISA results did not reflect the circulation of M. bovis in different infection status groups. However, these results were not unexpected, as the BioX ELISA has been found to have a much lower sensitivity than the MilA ELISA (Wawegama et al 2016, Petersen et al 2018. where M. bovis circulated for more than 1.5 years, 60 to 80% of young stock remained seropositive.…”

“…This ELISA has an estimated animal-level sensitivity and specificity of 94.3% and 94.4%, respectively using a cut-off of 105 antibody units (AU) (Wawegama et al, 2016). The MilA ELISA was performed as described previously (Wawegama et al 2014), with the concentration of M. bovis -specific antibodies in each sample calculated in antibody units (AU) by comparison with a series of standards on each plate using an ELISA analysis program (http://www.elisaanalysis.com), with a result of >135 AU interpreted as positive (Petersen et al 2018). The Bio K260 ELISA was performed according to the manufacturer's instructions.…”

“…Most previous studies have used other ELISAs and concluded that serum antibodies do not remain elevated for a prolonged period. Recently, Petersen et al (2018) studied M. bovis infected cows using the BioX ELISA and showed that serum antibody levels generally declined within 2 months after the onset of clinical disease. They concluded that serology is unlikely to be useful for individual diagnosis of disease associated with M. bovis in dairy cows.…”

Increased incidence rate of undesired early heifer departure in Mycoplasma bovis-antibody positive Danish dairy cattle herds

“…A proportion of cattle diseased from M. bovis will have a humoral immune response that can be measured using ELISA testing of antibodies in serum samples soon after the clinical signs are observed (Nicholas et al, 2002;Hazelton et al, 2018;Petersen et al, 2018a). It seems though that the antibody response to M. bovis is short lasting and can be difficult to interpret in young calves (Hazelton et al, 2018;Petersen et al, 2018a;Petersen et al, 2018b). Antibody measurements might be used to confirm or rule-out that M. bovis infection is associated with the observed disease syndromes during disease outbreaks, and a question often raised by farmers and veterinarians is whether to cull antibody-positive cattle.…”