We are currently running an Innovate funded GB wide longitudinal study on over 5000 dairy farms to evaluate the performance of the test. Three rounds of sampling has been conducted at an interval of 3-months between each sampling point. Testing of these samples has now been completed by NML.
The output of the results of this testing, will be evaluated against the bovine TB history of the participating herds, using the APHA database, by a team at SRUC. We hope that we will have initial data by late spring, and subject to Government approval, we will aim to keep the industry updated with our developing understanding of the outcomes of the study from that point forwards.
Fuller details of the objectives and study design can be found below.
Objective
To develop understanding on the value of the use of bulk tank milk surveillance using the Enferplex Bovine TB Antibody Test prior to its potential formal validation by the WOAH.
Specifically, the study will be focusing on:
- Test results obtained from herds currently under restriction. While the sensitivity of the test has already been elucidated for the WOAH submission, this was based on a single time point and repeating the test may enhance its sensitivity.
- How many herds currently designated Officially Tuberculosis Free (OTF) would be determined positive by the test.
- Understanding the relationship between seropositivity and herd bTB status.
- Understanding the predictive value of changes in seropositivity and/or the number of positive antigens for tracking progress, or otherwise, of herd bTB control measures.
- Assessing the use of the test as a monitoring tool for low risk OTF herds.
Data to date
Details of how the test detects infection by bovine tuberculosis (bTB) can be found by clicking here. Data to date shows that on bulk milk the test has a sensitivity of 77.7% and a specificity of 99.8%.
Study Design
Bulk milk samples from approximately 5,000 herds will be tested using the Enferplex bTB bulk milk test three times with an interval of 2-3 months. Herds under persistent restrictions and herds designated as OTF will be included from England, Wales and Scotland.
Methodology
Recruitment. The aim is to recruit approximately 5,000 UK dairy farms. We are working with the support of the UK’s milk processors to achieve this.
Each farm will be asked provide permission to have their bulk milk tested for bTB for the purposes of test development. This permission may be gained may be either via an opportunity for the individual farmer to either opt in or opt out of having their milk tested, this is to be discussed and agreed with the potential participating processors.
Testing. Enrolled farms would have their bulk milk tested every 2 to 3 months from the onset of the study until approximately September so that, if the test is approved by WOAH, all results will have been gained prior this point and therefore when the test is still an unvalidated test. A proportion of milk recorded herds will be tested monthly rather than every three months so that more detailed data can be obtained on the effect of changes in yield, constituents and herd size can be obtained.
Testing would occur at the National Milk Laboratories in Glasgow.
Data analysis
Results would be sent by NML to SRUC for analysis against their TB database if APHA allow SRUC an extension on their current agreement to perform this work. Results will be analysed to review correlation between herds deemed positive by the test and the herd status, the
- correlation of seropositivity with risk of bTB and the effect of changes of seropositivity on future outcomes.
- Analysis of any potential confounding effects on seropositivity of average days in milk, yield and herd size from milk recording data will also be undertaken.
- Study Report. The outputs of the analyses would be reported in an anonymised dataset to SureFarm Ltd, Enfer Scientific Ltd and MV Diagnostics Ltd.
- SureFarm Ltd, Enfer Scientific Ltd and MV Diagnostics Ltd would be responsible for reporting of the results to APHA and the scientific journals.
- The following are the analyses of the data that SRUC would perform. These are aimed to provide the necessary data to fulfil the objectives of the project set out previously.
The test’s ability to detect disease in herds currently under restriction
- Percentage of herds under TB restriction that test positive for each round of testing.
- Percentage of herds under TB restriction that test positive at one or more times within the study period.
- Herd level prevalence of TB against geographical area – use Defra/APHA regions to allow comparison.
How many herds currently designated OTF would be determined positive by the test?
- Percentage of herds that are currently OTF that test negative when tested for each round of testing.
- Percentage of herds that are currently OTF that consistently test negative within the study period.
- Of OTF herds that test positive, percentage of these that were under restriction within last calendar year, within two years, three years etc. up to 10 years.
- Of OTF herds that test positive, percentage of animal movements onto the farm within last calendar year, within two years, three years etc. up to five years.
- Of OTF herds that test positive, risk of being proximal to herd currently under restriction.
Future Work
- Odds ratio of a herd that has a positive result losing their OTF status within six months, within a year and within two years as opposed to a herd testing negative.
- Understanding whether there is relationship between seropositivity and antigen number and the risk of bTB breakdown.
- Analysis of whether there is a relationship between antibody load and the percentage of time the herd has been under TB restriction in the last one, two, three, four and five years.
- Analysis of whether there is a relationship between the number of positive antigens and the percentage of time the herd has been under TB restriction in the last one, two, three, four and five years.
- Analysis of whether there is a relationship between antibody load and the number of SICCT reactors disclosed at the previous and next skin test.
- Analysis of whether there is a relationship between the number of positive antigens and the number of SICCT reactors disclosed at the previous and next skin test.
- Are changes in the levels of seropositivity and or antigen number related to risk of a herd losing or regaining OTF status? (we would need to look at the level of change i.e., .0-10% increase, 10-20 % increase etc. rather than simply analyse via a rise or fall I suspect).
- In herds under restriction testing positive, analysis of whether the degree of antibody load increases the risk of the herd not regaining its OTF status within six months, within a year and within two years.
- In herds under restriction testing positive, analysis of whether the number of positive antigens increases the risk of the herd not regaining its OTF within six months, within a year and within two years.
- In OTF herds testing positive, analysis of whether the level of antibody load increases the risk of losing its OTF status within six months, within a year and within two years.
- In OTF herds testing positive, analysis of whether the number of positive antigens increases the risk of the herd losing its OTF status within six months, within a year and within two years.
Analysis of any potential confounding effects on seropositivity and antigen number
- Effect on seropositivity and antigen number of the average days in milk.
- Effect on seropositivity and antigen number of average yield.
- In herds under TB restriction, that receive a herd SICCT during the study period, the effect on antibody load and antigen number within one, two, three, four and five months post the test and on relative sensitivity.
- In OTF herds that receive a herd SICCT during the study period, the effect on antibody load and antigen number within one, two, three, four and five months post the test and the risk of the bulk tank testing positive. (This work will need to be done in conjunction with the duration the herd was OTF and percentage of movements onto the farm).
Other
- Potential for development of an algorithm that predicts risk of losing OTF status based on the data.
Regulatory dispensation
- Farmers will be advised that results of the outcome of the testing will not be reported to them.
- As a notifiable disease, we will have to report positive results to the relevant authorities as it is a legal requirement however there will be no repercussions from APHA/Defra and the devolved Governments for herds where the bulk milk tests positive, whether they are currently OTF or already under restriction. Letters to confirm this have been produced by all three Authorities.
- We will need to provide information on the numbers of participating trial herds and their regional distribution.
- We will need to provide an anonymised dataset of the study upon the completion of the trial, equivalent to what you would provide to an “open-access” scientific journal.
Reporting of results
We will be keen and happy to provide progress reports however the relevant authorities will require scrutiny of the data prior to any publication or reporting to third parties. There will be no reporting of National datasets.
What is the potential gain for bTB control and surveillance for bulk milk testing?
Herd surveillance for bTB in dairy herds via bulk tank milk, routinely collected from the farm, could potentially revolutionise bTB surveillance and control as:
- It is easy to obtain, robust, reliable and inexpensive to perform
- By allowing continuous monitoring of herds, it allows rapid detection of disease introduction thereby aiding eradication.
- By allowing an insight into the infection dynamics of the herd, it could allow for more bespoke and suitable control measures to be taken.
Permissions
Farms milk recording with NML, that agree to allow their recording data being used, will provide additional data on herd size and milk yield at the time of testing