Developing diagnostic technology to aid the detection, control and management of Johne’s disease on farm.
Effective diagnosis is essential to support any programme investigating or evaluating disease control, but challenging due to the nature of this disease.
The biology of Johne’s infection presents significant challenges for diagnostic tests. Most tests are designed to detect the presence of Johne’s bacteria directly (PCR or culture) or detect the host’s immune response to the infection (ELISA). However in the early stages of the disease the bacteria can remain hidden in the gut wall for many years with little or only intermittent shedding so that even highly sensitive tests such as the PCR (Polymerase Chain Reaction) are unable to detect Johne’s bacteria in routine clinical samples. Similarly, an immune response measured by serological tests like ELISA (Enzyme-Linked Immunosorbent Assay) will only develop once the disease has progressed. Therefore testing aimed at identifying the early subclinical stages of Johne’s infection is expensive and ineffective in practice.
As the disease progresses diagnosis becomes easier and more reliable as antibody levels rise and Johne’s bacteria are increasingly shed in faeces. Careful application of PCR and ELISA tests can be used to identify and rank Johne’s shedders (for deer and cattle) as well as clinical cases of Johne’s disease. The research recommends that focusing effort on identifying high-risk shedders that are spreading infection to young stock and becoming less productive will make diagnostic testing a highly effective tool to manage JD risks and reduce the economic and welfare impact of JD.
- Diagnostic workshop presentation, Johne’s Management Limited. 2015. Download here.
- Diagnostic test comparison, Abacus Bio Ltd. 2015 (publication pending).