Johne's disease
Mycobacterium avium subsp. paratuberculosis (MAP) is a causative agent of Johne's disease, which is a chronic granulomatous enteropathy in ruminants. In a study by Lim et al (2021) (Veterinary Research https://doi.org/10.1186/s13567-021-00905-1) whole genome-based alignment and comparative analysis were performed using 40 publicly available MAP genomes. The authors state that determining the genetic diversity of MAP is necessary to understand the epidemiology and biology of MAP, as well as establishing disease control strategies. First, whole genome-based alignment was employed to identify new genomic structures in MAP genomes. Second, the genomic diversity of the MAP population was described by pangenome analysis. A phylogenetic tree based on the core genome and pangenome showed that the MAP was differentiated into two major types (C- and S-type), which was in keeping with the findings of previous studies. Finally, functional analysis of the pangenome was performed using three virulence factor databases to predict the phenotypic diversity of MAP in terms of pathogenicity. Based on the results of the pangenome analysis, the research team developed a real-time PCR technique to distinguish among S-, B- and C-type strains. In conclusion, the results of their study suggest that the phenotypic differences between MAP strains can be explained by their genetic polymorphisms. Perhaps in future we will not simply try to determine if MAP is, or is not, present on a farm, but will use much refined approaches considering both the genotype and phenotype of the MAP on our client's farms.
Cell-mediated immune responses to MAP are regulated by various types of T lymphocytes. In another recently published paper by Jenvey et al (2021) (Veterinary Research https://doi.org/10.1186/s13567-021-00925-x) the aim of research was to quantitate T cell subsets in the midileum of cows naturally infected with MAP to identify differences during stages of infection, and to determine whether these subsets could be used as predictors of disease state. Immunofluorescent (IF) labelling of T cell subsets and macrophages was performed on frozen mid-ileal tissue sections archived from naturally infected dairy cows in either subclinical or clinical disease status, and noninfected control cows. Comprehensive IF staining for CD4, CD8α, TcR1-N24 (gamma delta), FoxP3, CXCR3 and CCR9 served to define T cell subsets and was correlated with macrophages present. Clinically affected cows demonstrated significantly higher numbers of CXCR3+ (Th1-type) and CCR9+ (total small intestinal lymphocytes) cells at the site of infection compared with the subclinical cows and noninfected controls. Further, predictive modelling indicated a significant interaction between CXCR3+ and AM3K+ (macrophages) cells, suggesting that progression to clinical disease state aligns with increased numbers of these cell types at the site of infection. The ability to predict disease state with this model was improved from previous modelling using immunofluorescent macrophage data. Predictive modelling indicated an interaction between CXCR3+ and AM3K+ cells, which could more sensitively detect subclinical cows compared with clinical cows. In future it may be possible to use this knowledge to improve and develop an assay to detect subclinically infected animals with more confidence during the early stages of the disease. Both these papers give some insight into how our diagnosis and control of Johne's disease may change and improve further in the future using new technologies.
Pain management and sedation
The use of local anaesthesia and a nonsteroidal anti-inflammatory drug (NSAID) can reduce in-dicators of pain and inflammation in calves following disbudding. The objective of a study by Reedman et al (2021) (https://doi.org/10.3168/jds.2020-19689) was to evaluate the effects of xy-lazine sedation in conjunction with a local anaesthetic and an NSAID in calves undergoing cautery disbudding. 122 group-housed female and male Holstein calves fed milk with automated feeders, aged 13 to 44 d, were enrolled over 9 replicates and randomly allocated to 1 of 2 treatments: (1) sedated: lidocaine cornual nerve block, 0.5 mg/kg meloxicam (administered subcutaneously) and 0.2 mg/kg xylazine (administered in-tramuscularly), or (2) non-sedated: lidocaine cornual nerve block and meloxicam. Outcomes collected consisted of feeding behaviour, latency to drink milk following disbudding, play behaviour (induced by adding bedding), lying behaviour, mechanical nociceptive threshold (MNT, measured using a pressure force algometer), struggling behaviour during disbudding, length of time to administer the nerve block, length of time to disbud, and serum haptoglobin concentrations. There were no detected differences between the treatment groups in mean daily milk consumption in the 72h following disbudding. Sedated calves had reduced average milk drinking speed from 0 to 24h and 24 to 48h following disbudding compared with non-sedated calves, but no difference was detected from 48 to 72 h. Sedated calves had reduced MNT at 0, 60, and 240 min after disbudding, but no differences were detected between groups at 24h after disbudding. Non-sedated calves had 4.5 times the odds of struggling more than twice during the disbudding procedure compared with sedated calves, and it took less time to administer a nerve block to sedated calves compared with non-sedated. At +3h, non-sedated calves were 79 times more likely to play compared with sedated calves, and 24h after disbudding, sedated calves were 2 times more likely to play compared with non-sedated calves. The results indicate that calves sedated with xylazine for cautery disbudding responded less to painful stimuli (disbudding and MNT) both during and following the procedure and had a higher rate of play behaviour 24h following sedation compared with the non-sedated calves, but xylazine may also have a prolonged carryover effect that affects suckling behaviour for 48h following sedation.