Mycoplasma bovis outbreak in New Zealand cattle: An assessment of transmission trends using surveillance data

A longitudinal study of the dynamics of Mycoplasma bovis antibody status in primiparous cows and bulk tank milk in Swedish dairy herds

Mycoplasma bovis is an important pathogen causing pneumonia, mastitis, and arthritis in cattle all over the world entailing reduced animal welfare and economic losses. In this longitudinal study, we investigated the presence of M. bovis antibodies in bulk tank milk (BTM) and in milk from primiparous (PP) cows at 4 sampling occasions over 2 yr. Herd characteristics associated with a positive antibody test result in PP cows were investigated. The participating dairy herds (n = 149) were situated in southern Sweden, samples were collected and analyzed with ID Screen antibody ELISA. Information on herd characteristics was retrieved from the national DHI database. To identify herd characteristics associated with the presence of antibodies in PP cows, mixed linear regression with herd and sample as random factors were used. The apparent herd-level prevalence of M. bovis infection based on antibodies in BTM was 17%, but with the addition of PP cows, the prevalence increased to 28%. The results showed that larger herds and introduction of cattle was associated with higher antibody levels in PP cows. In conclusion, this study showed a clear difference in the apparent prevalence of M. bovis infection based on antibodies in BTM or in PP cows: The number of positive herds was almost doubled when including PP cows. This motivates repeated sampling of a few PP cows to find newly infected herds in an early stage. Finally, the results showed that introduction of cattle influences the level of M. bovis antibodies. This is important in the control and prevention of further spread of the infection. It is essential for free herds to know their M. bovis status, and antibody testing is highly recommended if introducing cattle.

Comparison of DNA extraction procedures for detection of Mycoplasma bovis directly from extended bovine semen straw samples using a commercial M. bovis PCR

BACKGROUND

Mycoplasma bovis is a global pathogen of cattle but was detected for the first time in New Zealand in 2017, triggering a response under their Biosecurity Act as an "unwanted organism". Following a lengthy eradication campaign, the Ministry of Primary Industries (MPI) now requires all bovine semen destined for export to New Zealand to be screened with an M. bovis-specific real-time PCR (rtPCR) compliant with amended import health standard (IHS) test requirements aimed at preventing the accidental importation of M. bovis. The standard stipulates that semen samples cannot be centrifuged prior to DNA extraction. To comply with these strict requirements, one of the listed tests was validated together with different DNA preparation steps and compared with existing in-house procedures. DNA was extracted from semen straws using the current in-house semi-automated platform procedures for processing culture, tissue and body fluid sample submissions and was compared with the stipulated test requirements. DNA from centrifuged and unspun semen samples spiked with M. bovis was also compared.

RESULTS

The rtPCR had a sensitivity and specificity of 100% (95% confidence interval = 79-100% and 74-100%, respectively) when testing DNA from other Mycoplasma species or bovine semen spiked with the latter, with a high level of repeatability for within- and between- run replicates. The consistent limit of detection was 0.001 pg/µl M. bovis DNA and between 5.3 × 102 and 7.5 × 102 CFU/ml M. bovis when artificially spiked in semen. DNA extracted using the KingFisher Flex was detected with lower Cq values than the Maxwell 16, but the comparable improvements in sensitivity were mainly associated with non-centrifuged samples (p < 0.001). None of the procedures tested impeded the detection sensitivity of M. bovis in the presence of competitor organisms Acholeplasma laidlawii, Mycoplasma bovigenitalium and Ureaplasma diversum, confirming M. bovis specificity of the polC target.

CONCLUSIONS

Under the experimental conditions applied, this rtPCR test efficiently detected M. bovis in extended bovine semen straw samples from DNA extracted using both semi-automated extraction platforms, irrespective of prior centrifugation of extended semen.

Dairy farmer, engagement and understanding of One Health and antimicrobial resistance - a pilot survey from the lower north island of Aotearoa New Zealand

BACKGROUND

Reducing antimicrobial resistance (AMR) requires a multidisciplinary One Health approach, which necessitates buy-in from all stakeholders. In Aotearoa New Zealand, where the dairy industry is one of the largest users of antimicrobials, there are ongoing efforts to optimise antimicrobial usage (AMU) to minimise the development of AMR. These include regulations around the veterinary authorisation of the use of antibiotics by farmers without the need for a specific prescription ("the RVM process") and programmes such as the New Zealand Veterinary Association's antibiotic 'Traffic Light System'. The goal of this pilot survey was to develop and trial a questionnaire to determine how much Aotearoa dairy farmers understand about One Health, AMR, the RVM process and how their actions regarding AMU affect the wider environment.

METHODS

A 55-question semi-structured questionnaire was piloted on 15 dairy farms in the Lower North Island of Aotearoa New Zealand via an in-person semi-structured interview between September and November 2021.

RESULTS

None of the interviewed farmers could define the term One Health. However, the majority found the RVM process to be of use on their farm, although admitted they generally felt frustration regarding AMR, seeing it as a blockage to productivity, and lacked awareness regarding how their actions were related to its development. Of the farmers interviewed over half had not heard of the traffic light system, and of those who had, one admitted they refused to adhere to it.

CONCLUSIONS

This survey's novel findings have highlighted that there are notable gaps within dairy farmer understanding of AMU, AMR and One Health as well as highlighting that veterinarians could do more to keep their clients informed of their important role within One Health. There is still a lot more work to do with regards to vets, farmers and industry representatives working together to embrace One Health. Simple solutions would be to encourage farmers returning unused drugs to their veterinarians for correct disposal and to actively engage farmers further regarding AMU and AMR, so that these end-product users do not feel disconnected from the process.

Diagnostic performance of Mycoplasmopsis bovis antibody ELISA tests on bulk tank milk from dairy herds

BACKGROUND

Testing of bulk tank milk (BTM) for Mycoplasmopsis bovis (previously Mycoplasma bovis) antibodies is increasingly popular. However the performance of some commercially available tests is unknown, and cutoff values possibly need to be adjusted in light of the purpose. Therefore, the aim of this study was to compare the diagnostic performance of three commercially available M. bovis antibody ELISAs on BTM, and to explore optimal cutoff values for screening purposes. A prospective diagnostic test accuracy study was performed on 156 BTM samples from Belgian and Swiss dairy farms using Bayesian Latent Class Analysis. Samples were initially classified using manufacturer cutoff values, followed by generated values.

RESULTS

Following the manufacturer's guidelines, sensitivity of 91.4%, 25.6%, 69.2%, and specificity of 67.2%, 96.8%, 85.8% were observed for ID-screen, Bio K432, and Bio K302, respectively. Optimization of cutoffs resulted in a sensitivity of 89.0%, 82.0%, and 85.5%, and a specificity of 83.4%, 75.1%, 77.2%, respectively.

CONCLUSIONS

The ID-screen showed the highest diagnostic performance after optimization of cutoff values, and could be useful for screening. Both Bio-X tests may be of value for diagnostic or confirmation purposes due to their high specificity.

Genome-wide phylodynamic approach reveals the epidemic dynamics of the main Mycoplasma bovis subtype circulating in France

Mycoplasma bovis is a major aetiological agent of bovine respiratory disease worldwide. Genome-based analyses are increasingly being used to monitor the genetic diversity and global distribution of M. bovis, complementing existing subtyping schemes based on locus sequencing. However, these analyses have so far provided limited information on the spatiotemporal and population dynamics of circulating subtypes. Here we applied a genome-wide phylodynamic approach to explore the epidemic dynamics of 88 French M. bovis strains collected between 2000 and 2019 in France and belonging to the currently dominant polC subtype 2 (st2). A strong molecular clock signal detected in the genomic data enabled robust phylodynamic inferences, which estimated that the M. bovis st2 population in France is composed of two lineages that successively emerged from independent introductions of international strains. The first lineage appeared around 2000 and supplanted the previously established antimicrobial-susceptible polC subtype 1. The second lineage, which is likely more transmissible, progressively replaced the first M. bovis st2 lineage population from 2005 onward and became predominant after 2010. Analyses also showed a brief decline in this second M. bovis st2 lineage population in around 2011, possibly due to the challenge from the concurrent emergence of M. bovis polC subtype 3 in France. Finally, we identified non-synonymous mutations in genes associated with lineages, which raises prospects for identifying new surveillance molecular markers. A genome-wide phylodynamic approach provides valuable resources for monitoring the evolution and epidemic dynamics of circulating M. bovis subtypes, and may prove critical for developing more effective surveillance systems and disease control strategies.

Mycoplasma bovis testing for the screening of semen imported into New Zealand

AIMS

To evaluate the fitness of three PCR assays for the detection of Mycoplasma bovis in dilute (extended) bovine semen, and a reverse transcriptase-PCR (RT-PCR) adaptation as a proxy for viability.

MATERIALS AND METHODS

Four commercial kit-based methods for nucleic acid extraction were compared to test for the presence of PCR inhibitors in nucleic acid extracted from undiluted and diluted semen. Then, analytical sensitivity, analytical specificity, and diagnostic specificity of two real-time PCR and one conventional PCR were evaluated for the detection of M. bovis DNA in semen and compared against microbial culture. Furthermore, an RT-PCR was adapted to detect RNA only and tested on viable and non-viable M. bovis to establish its ability to discriminate between the two.

RESULTS

No significant PCR inhibition was detected from the dilute semen. All DNA extraction methods except one were equivalent, regardless of semen dilution. The analytical sensitivity of the real-time PCR assays was estimated as 45.6 cfu per 200 µL semen straw (2.2 × 10² cfu/mL). The conventional PCR was 10 times less sensitive. No cross-reactivity was observed for the real-time PCR for any of the bacteria tested and the diagnostic specificity was estimated as 100 (95% CI = 94.04-100) %. The RT-PCR was poor in distinguishing between viable and non-viable M. bovis. The mean quantification cycle (Cq) values for RNA extracted from different treatments to kill M. bovis remained unchanged 0-48 hours after inactivation.

CONCLUSION AND CLINICAL RELEVANCE

The real-time PCR were fit for the purpose of screening dilute semen for the detection of M. bovis to prevent incursion via importation of infected semen. The real-time PCR assays can be used interchangeably. The RT-PCR could not reliably indicate the viability of M. bovis. Based on the results from this study, a protocol and guidelines have been produced for laboratories elsewhere that wish to test bovine semen for M. bovis.

Comparison and optimisation of screening cutoff values for Mycoplasma bovis antibody ELISAs using serum from youngstock

BACKGROUND

Mycoplasma bovis-associated disease can cause tremendous production losses, welfare issues and high antimicrobial use. Therefore, screening cattle for M. bovis antibodies before entering the herd is a popular and possibly cost-efficient way to reduce disease introduction. However, interpretation of results can be challenging due to variable accuracy between tests and populations. This study's objectives were to compare the diagnostic test accuracy of three commercially available M. bovis antibody ELISAs (ID-screen, Bio K302 and Bio K432) and to explore optimal cutoff values for screening purposes.

METHODS

A prospective diagnostic test accuracy study was performed on 170 serum samples from youngstock using Bayesian latent class modelling. Samples were categorised using manufacturer and generated cutoff values.

RESULTS

Using the manufacturers' guidelines, ID-screen, Bio K432 and Bio K302 showed 97.6%, 67.4% and 33.6% sensitivity, and 78.8%, 97.6% and 99.1% specificity, respectively. Optimised cutoffs resulted in 94.8%, 82.6% and 78.3% sensitivity, and 94.2%, 92.5% and 79.4% specificity, respectively.

CONCLUSIONS

The highest diagnostic accuracy for detecting M. bovis antibodies was obtained by ID-screen (≥110%). However, by adjusting cutoff values, the sensitivity of Bio-X tests could be markedly increased, making these tests also applicable as screening tools.

LIMITATIONS

Interpretation needs to be careful as antibodies may be linked to both infectious and non-infectious status.

Genome Editing of Veterinary Relevant Mycoplasmas Using a CRISPR-Cas Base Editor System

Mycoplasmas are minimal bacteria that infect humans, wildlife, and most economically relevant livestock species. Mycoplasma infections cause a large range of chronic inflammatory diseases, eventually leading to death in some animals. Due to the lack of efficient recombination and genome engineering tools for most species, the production of mutant strains for the identification of virulence factors and the development of improved vaccine strains is limited. Here, we demonstrate the adaptation of an efficient Cas9-Base Editor system to introduce targeted mutations into three major pathogenic species that span the phylogenetic diversity of these bacteria: the avian pathogen Mycoplasma gallisepticum and the two most important bovine mycoplasmas, Mycoplasma bovis and Mycoplasma mycoides subsp. mycoides. As a proof of concept, we successfully used an inducible SpdCas9-pmcDA1 cytosine deaminase system to disrupt several major virulence factors in these pathogens. Various induction times and inducer concentrations were evaluated to optimize editing efficiency. The optimized system was powerful enough to disrupt 54 of 55 insertion sequence transposases in a single experiment. Whole-genome sequencing of the edited strains showed that off-target mutations were limited, suggesting that most variations detected in the edited genomes are Cas9-independent. This effective, rapid, and easy-to-use genetic tool opens a new avenue for the study of these important animal pathogens and likely the entire class Mollicutes.

IMPORTANCE Mycoplasmas are minimal pathogenic bacteria that infect a wide range of hosts, including humans, livestock, and wild animals. Major pathogenic species cause acute to chronic infections involving still poorly characterized virulence factors. The lack of precise genome editing tools has hampered functional studies of many species, leaving multiple questions about the molecular basis of their pathogenicity unanswered. Here, we demonstrate the adaptation of a CRISPR-derived base editor for three major pathogenic species: Mycoplasma gallisepticum, Mycoplasma bovis, and Mycoplasma mycoides subsp. mycoides. Several virulence factors were successfully targeted, and we were able to edit up to 54 target sites in a single step. The availability of this efficient and easy-to-use genetic tool will greatly facilitate functional studies of these economically important bacteria.

Seroprevalence of Mycoplasma bovis in bulk milk samples in Irish dairy herds and risk factors associated with herd seropositive status

Mycoplasma bovis is a serious disease of cattle worldwide; mastitis, pneumonia, and arthritis are particularly important clinical presentations in dairy herds. Mycoplasma bovis was first identified in Ireland in 1994, and the reporting of Mycoplasma-associated disease has substantially increased over the last 5 years. Despite the presumed endemic nature of M. bovis in Ireland, there is a paucity of data on the prevalence of infection, and the effect of this disease on the dairy industry. The aim of this observational study was to estimate apparent herd prevalence for M. bovis in Irish dairy herds using routinely collected bulk milk surveillance samples and to assess risk factors for herd seropositivity. In autumn 2018, 1,500 herds out of the 16,858 herds that submitted bulk tank milk (BTM) samples to the Department of Agriculture testing laboratory for routine surveillance were randomly selected for further testing. A final data set of 1,313 sampled herds with a BTM ELISA result were used for the analysis. Testing was conducted using an indirect ELISA kit (ID Screen Mycoplasma bovis). Herd-level risk factors were used as explanatory variables to determine potential risk factors associated with positive herd status (reflecting past or current exposure to M. bovis). A total of 588 of the 1,313 BTM samples were positive to M. bovis, providing an apparent herd prevalence of 0.45 (95% CI: 0.42, 0.47) in Irish dairy herds in autumn 2018. Multivariable analysis was conducted using logistic regression. The final model identified herd size, the number of neighboring farms, in-degree and county as statistically significant risk factors for herd BTM seropositivity to M. bovis. The results suggest a high apparent herd prevalence of seropositivity to M. bovis, and evidence that M. bovis infection is now endemic in the Irish dairy sector. In addition, risk factors identified are closely aligned to what we would expect of an infectious disease. Awareness raising and education about this important disease is warranted given the widespread nature of exposure and likely infection in Irish herds. Further work on the validation of diagnostic tests for herd-level diagnosis should be undertaken as a matter of priority.

Development of a Multiplex Droplet Digital PCR Assay for the Detection of Babesia, Bartonella, and Borrelia Species

We describe the development, optimization, and validation of a multiplex droplet digital PCR (ddPCR) assay for the simultaneous detection of Babesia, Bartonella, and Borrelia spp. DNA from several sample matrices, including clinical blood samples from animals and humans, vectors, in-vitro infected human and animal cell lines, and tissues obtained from animal models (infected with Bartonella and/or B. burgdorferi). The multiplex ddPCR assay was able to detect 31 Bartonella, 13 Borrelia, and 24 Babesia species, including Theileria equi, T. cervi, and Cytauxzoon felis. No amplification of Treponema or Leptospira spp. was observed. Sensitivity of 0.2-5 genome equivalent DNA copies per microliter was achieved for different members of the Bartonella and Borrelia genus, depending on the species or matrix type (water or spiked blood DNA) tested. The ddPCR assay facilitated the simultaneous detection of co-infections with two and three vector-borne pathogens comprising four different genera (Babesia, Bartonella, Borrelia, and Theileria) from clinical and other sample sources.