Polypeptide Fragment Skin Test for Bovine Tuberculosis Differentiation
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Solution Overview
Problem
Current diagnostic methods for bovine tuberculosis, such as the tuberculin skin test, face challenges in differentiating infected animals from those vaccinated with BCG, and are not suitable for regions with high exposure to environmental mycobacteria, leading to reduced sensitivity and specificity.
Innovation Solution
Development of polypeptide fragment skin test diagnostic reagents comprising specific 40mer fragments of ESAT-6, CFP-10, and Rv3615c antigens, which provide improved sensitivity and specificity by eliciting a positive result in infected animals while avoiding cross-reactivity with vaccinated animals and environmental mycobacteria.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If purified protein derivative (PPD) extracts from heat-killed mycobacteria cultures are used in skin tests, then the test can detect mycobacterium infections, but the test cannot differentiate between infected animals and those vaccinated with BCG due to cross-reactive antigens
Solution Approach 1:
The patent segments the whole cell antigen into specific protein components by identifying and isolating antigens that are present in field strains but absent or not immunogenic in BCG vaccine strain. This segmentation allows the test to detect infections caused by specific mycobacteria while ignoring responses from BCG vaccination.
Solution Approach 2:
The patent extracts specific antigens (such as ESAT-6, CFP-10, and other early secreted antigens) from the complex whole cell antigen preparation. By taking out only the relevant antigens that differentiate between infection and vaccination, the test achieves both sensitivity and specificity.
2Ease of manufacture
If crude whole cell antigen preparation is used in tuberculin skin test, then the test can be performed with available materials, but the presence of cross-reactive antigens renders the test unable to differentiate infected from vaccinated animals
Solution Approach 1:
The patent changes the parameters of antigen preparation from crude whole cell extracts to purified or recombinant specific protein antigens. This parameter change maintains ease of production through recombinant technology while dramatically improving diagnostic specificity by eliminating cross-reactive antigens.
Solution Approach 2:
The patent uses composite approaches by combining multiple specific antigens (ESAT-6, CFP-10, and other early secreted antigens) into a diagnostic reagent mixture. This composite material provides both the simplicity of standardized production and the specificity needed to differentiate infection from vaccination.
3Measurement precision
If single intradermal comparative cervical tuberculin test (SICCT) is used to improve test specificity in regions with high exposure to environmental mycobacteria, then test specificity improves, but assay sensitivity is reduced
Solution Approach 1:
The patent extracts only the specific antigens relevant to bovine tuberculosis (ESAT-6, CFP-10, early secreted antigens) that are not present in environmental mycobacteria. This extraction allows the test to maintain high sensitivity by detecting M. bovis infections while achieving high specificity by ignoring environmental mycobacteria that do not produce these specific antigens.
Data Source
AI summary
There is provided a skin test diagnostic reagent comprising: at least one 40mer polypeptide consisting of any one of SEQ ID NOs: 1, 3 or 4; at least one 40mer polypeptide consisting of any one of SEQ ID NOs: 7 or 8; and at least one 40mer polypeptide consisting of any one of SEQ ID NOs: 10, 11 or 12, characterised in that the reagent elicits a positive result when administered in a skin test to an animal infected with Mycobacterium bovis or Mycobacterium tuberculosis.