Tuberculosis testing in deer
The Animal Health and Welfare Panel of EFSA was invited by the European Commission to issue a scientific opinion on the suitability of existing tuberculosis (TB) tests in deer for the purpose
of granting official TB-free status in the framework of Directive 92/65/lEEC, on the modalities for the validation of such tests and a definition, including options for possible testing
regimes, giving sufficient guarantees for a animal/holding/region to be qualified/ maintained/ regained as officially free from TB infection in deer. It was also agreed that the opinion should
consider testing in relation to trade in animals between countries that are not free from TB, noting that any requirements for testing will facilitate efforts towards future TB freedom in these
The report focuses on farmed deer. The role of wildlife species was only considered due to the risk posed to farmed deer. Relevant deer species and the farmed deer industry are described in the
opinion. TB in deer is generally a slowly progressing disease, with lesions similar to those observed in cattle. TB-infected deer present a public health hazard, and can act as a reservoir for
the infection of livestock and wildlife, including protected and endangered species.
Fourteen diagnostic tests were assessed for their performance (sensitivity – Se; specificity – Sp), repeatability, reproducibility and practicality. The suitability of these tests varied
according to the stage of infection and the component of the immune response being measured. The cell mediated immune response predominates during initial stages of infection, and circulating
antibodies during later stages. A combination of different tests («combined tests») suitable for both phases of infection is often used to diagnose tuberculosis in a holding with
unknown infection status. Infected animals may appear clinically healthy in spite of advanced lesions.
The Se and Sp of these diagnostic tests were quantitatively assessed using two sources of information; expert opinion and systematic literature review. Using a meta-analysis, these data were
combined, and Bayesian logistic regression models were used to estimate the diagnostic Se and Sp.
At any given time, it is highly unlikely that all infected animals in an infected herd will be detected, either using a single test or any combination of tests. Testing will have to be repeated
on at least a second occasion to provide any degree of certainty concerning freedom from infection.
The two intradermal tuberculin tests (comparative: SICCT and single: SST) are currently the only tests suitable for large scale screening in live animals. These tests are primarily intended for
the detection of TB on a herd basis. When validated for use in deer, gamma-interferon assay (GINT) and ELISA in combination with SICCT and SST have the potential to maximize detection of
Interference (immunosuppression) with previous tests is reported for a period of 60 days but not at 120 days. Therefore, a minimum test interval of 120 days is recommended to be applied for
Meat inspection is currently the only method suitable for large scale screening in slaughtered animals. The final confirmation is through the identification of species within the M.
tuberculosis complex by culture following necropsy and usually in combination with histology.
Validation of diagnostic tests in deer is similar to validation of tests for tuberculosis in non-deer species. Realistic estimates of test Se and Sp can only be calculated if data are available
from surveillance studies under field conditions.
It is recommended that freedom be defined as a prevalence of infection that is lower than the designated design prevalence. This recommendation is made under the condition that adequate and
ongoing surveillance and control measures are in place. It is also recommended that an output based standard is used, based on a specified and desired probability of freedom from infection.
Recommendations are made for the levels of freedom to be applied at animal, at holding and at country levels; thus an officially free animal is an animal that comes from an officially free
A modelling approach was used to assess the ability of a range of testing strategies, to achieve, maintain and regain the recommended proof-of-freedom from TB in deer, when applied in a variety
of scenarios with different probabilities of introduction of new infection. A testing interval of one year has been assumed.
The risk of introduction of TB infection to new holdings through movement of TB- infected deer plays a significant role in determining the amount of testing that is required to achieve the
required probability of freedom. Two separate routes of infection are considered: contact with wildlife (e.g. badgers and wild deer) or farmed non-deer species (e.g. cattle) «outside the
fence» and, secondly, from animals brought ‘inside the fence’ through the introduction of infected deer. The risk of introduction from non deer farmed species is likely to be proportional
to the TB prevalence of the region, zone or Member State (MS) of the holding. It is recommended that each MS clarifies the risk posed by wildlife species. For an adequately fenced holding, the
risk from wildlife and non-deer farmed species is estimated to be reduced by 90%. Demonstration of freedom using the available tests is only possible when the probability of introduction is
relatively low (approx. < 10%). Based on the model applied, examples of different testing regimes are presented in the opinion.
For the movement of animals between non-free holdings, a simplified approach is recommended based on a suggested system of holding classification. Animals may only be moved between holdings of
the same status (except restricted holdings, from which no movements are permitted) and from holdings of a higher status to holdings of a lower status. No testing should be required for any of
the these movements, except for movements between untested herds, in which case each of the animals moved should be tested with either of the two (SST or SICCT) intradermal tests (or the ELISA
or GINT, when they have been validated).
Appropriate testing facilities are needed to ensure that animal welfare is not compromised.