final report - ARCHIVE: Defra

Diagnosis
2.3.2 Conventional microscopy and culture-based detection remain valuable confirmatory techniques. While
various technical advances continue to be introduced in the laboratory culture of mycobacteria, some
of which may achieve enhancements in numbers of bacilli recovered (Biketov et al., 2000; Sweeney et
al., 2006), we do not attach priority to research in this area for the reasons outlined in 2.3.1.
2.3.3 As with Mtb, it has been difficult to achieve consistent sensitivity results with nucleic acid (DNA
or RNA) amplification tests. However, there are several promising developments in the diagnosis of
human TB in this area (Perkins & Cunningham, 2007). Ultimately, such tests may partially replace
culture confirmation but again we do not attach priority to this area; this is partly due to the extensive
efforts to produce economic and sensitive tests for Mtb and partly again for the reasons outlined in
2.3.1.
2.3.4 Antigen and antibody detection: In many infectious diseases, diagnosis may be achieved by detecting
a highly specific component(s) of the causal organism that can be recognized with an antibody
preparation or by detecting antibodies made by the infected individual against such components.
While antigen tests are not used in bTB, there has been a considerable resurgence of interest in this
field in human TB. Specific detection of such molecules as lipoarabinomannan in urine holds out some
promise (Boehme et al., 2005; Perkins & Cunningham, 2007). In this field, as in many others, we
advise a watching brief on developments in human TB. At some point, it could be worth adapting tests
developed for human investigations for use in cattle. It is possible, however, that these tests may be
compromised by exposure to environmental mycobacteria, including Mycobacterium paratuberculosis.
2.3.5 Several tests for detection of antibodies against Mb in cattle are available. Without exception, these do
not achieve sufficient sensitivity or specificity to be of value in the UK control programme. We consider
it unlikely that a conventionally developed antibody test will be of value. However, new techniques
to precisely map the B-lymphocyte response to the entire proteome of micro-organisms have opened
up this field (Zhu et al., 2006) and to date have not been tested for their potential in the context of
diagnosis of bTB. These rely on high-throughput, large-scale in vitro expression of the proteome of an
organism once its genome has been sequenced. By transferring these products to microarray chips, up
to several thousand individual proteins can be screened using sera from infected/vaccinated animals to
define the immunogenic determinants. It may be possible to perform this using expressed proteomes
from Mtb, Mb and environmental mycobacteria to identify potentially useful and specific antigens for
an antibody-based diagnostic test.
2.3.6 Tests of cell-mediated immunity: It has recently become possible to detect specific immune responses
to antigens that do not elicit antibodies (T lymphocyte-stimulating antigens) in an amenable test format
(e.g. Bovigam). These tests have made a considerable impact on the assessment of TB infection in both
human and bovine contexts (Pai et al., 2004; Vordermeier et al., 2006). In general, the cells in the
animal’s blood are stimulated with T-cell antigens specific to Mb and the responses are measured by
quantifying mediator proteins (cytokines) manufactured or released as a result. The Bovigam test uses
Mb tuberculin as the antigen mix and g-IFN as the detected cytokine. There is considerable room for
further development of these tests.
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