New reporting classifications for Mycoplasma bovis
From April 2019, we changed the way we classify affected properties. Find about the new classifications and why we made the changes.
New classifications – easier and clearer
We are changing how we report the number of properties affected by Mycoplasma bovis. The changes will make clearer the relative scale of the incursion and our progress towards eradication.
The 3 new classifications introduced in April 2019 are:
- Confirmed Properties – all properties over time that have been determined to have had Mycoplasma bovis.
- Active Properties – properties with Mycoplasma bovis that are currently under a Restricted Place Notice, and are pending or going through depopulation and cleaning and disinfection.
- Cleared Properties – properties that have had Mycoplasma bovis and have been depopulated, cleaned and disinfected, and have had restrictions lifted.
All Confirmed Properties have been or will be depopulated.
It's always been the goal of the eradication programme to be transparent and open. We think these changes give an easier and clearer understanding of the progress of the programme.
Why the change?
The independent Mycoplasma bovis Technical Advisory Group (TAG) recommended this change in its most recent report (24 January 2019). The Ministry for Primary Industries (MPI's) chief science adviser subsequently reviewed how we were using classifications, and if they could be improved to meet the latest scientific developments in the programme.
Report [PDF, 873 KB]
Limitations with old classifications
Since the beginning of the response in 2017, we have reported the total number of Restricted Places, as well as the total number of Infected Properties (a subset of the Restricted Places).
Infected Property classification
Infected Property is an epidemiological term. It means a property has had Mycoplasma bovis confirmed through a DNA sequenced PCR test result. Infected Property is a very high threshold and the PCR has significant limitations.
The other way we test for Mycoplasma bovis is using the ELISA technique. As we have gained more experience and data using this testing method we are increasingly confident in confirming Mycoplasma bovis using ELISA. However, many properties that have been determined to have had Mycoplasma bovis through ELISA testing did not provide positive PCR results until after they were depopulated, and therefore couldn't be classified as Infected Properties.
Restricted Place classification
A Restricted Place is a legal definition, which means that we have determined that Mycoplasma bovis is present on the property using either PCR or ELISA testing. All animal movements have been restricted, and the property will be depopulated.
Restricted Place also misses a small number of early properties, as it cannot be declared retrospectively. In a small number of cases, the infection is confirmed when there are no animals left on the property, and these cannot be declared a Restricted Place.
Restricted Place Notices will still be used by the programme. However, we will no longer report the number of Restricted Places, as this will be captured under the Active Property classification.
When is a property determined to have had M. bovis?
A Confirmed Property is a property that is determined by the programme's epidemiologists to have met the definition for having Mycoplasma bovis that:
- has returned a positive PCR result, or
- serology levels (through ELISA testing) indicate that the disease is, or was, present, or
- has had repeated marginal serology results combined with other risk factors, indicating the disease is present, and that depopulation is the only responsible decision to achieve eradication.