Test performance data demonstrates utility of a cattle DIVA skin test reagent (DST-F) compatible with BCG vaccination

Abstract

Bacillus Calmette-Guérin (BCG), an attenuated strain of Mycobacterium bovis (M. bovis), is the lead candidate vaccine for control of bovine tuberculosis (TB) in cattle. However, BCG vaccination sensitises cattle to bovine tuberculin, thus compromising the use of the current bovine TB surveillance tests. To address this, we have developed a diagnostic skin test that is not compromised by BCG vaccination and is able to detect BCG vaccinated animals that subsequently develop bovine TB following exposure to M. bovis. Building on previous work using ‘in house’ formulated protein cocktail reagents, we herein present test performance data for a single fusion protein (DST-F) containing the mycobacterial antigens ESAT-6, CFP-10 and Rv3615c formulated as a ‘ready to use’ reagent by a commercial manufacturer. Our results demonstrate that, unlike tuberculin reagents, a diagnostic skin test using DST-F maintained high specificity in BCG vaccinated animals. Furthermore, the DST-F skin test demonstrated a high relative sensitivity in identifying M. bovis infected animals, including those where BCG vaccination failed to prevent bovine TB pathology following experimental exposure to M. bovis. The DST-F is currently undergoing field trials in Great Britain to support its licensure and commercialisation.

Protective Efficacy of BCG Vaccination in Calves Vaccinated at Different Ages

“…As many as 80% of calves vaccinated with BCG were reported to give skin test responses until at least 6 months after vaccination [ 35 ]. To overcome this, defined antigen combinations (antigens present in M. bovis but absent in BCG) have extensively been explored, and a DIVA skin test has been described that enables the differentiation of BCG-vaccinated individuals [ 5 , 20 , 36 , 37 ]. Field-testing of this DIVA skin test alongside BCG vaccination is now underway in the UK [ 38 ].…”

“…This interference in specificity of diagnostic tests has hampered the deployment of BCG vaccination in the field. However, the use of a recently developed DIVA skin test (DST) [ 18 , 19 , 20 ] will enable the differentiation of M. bovis -infected from BCG-vaccinated animals, further facilitating the deployment of BCG in the field.…”

Vaccination Strategies in a Potential Use of the Vaccine against Bovine Tuberculosis in Infected Herds

“…The compatibility of BCG with a fusion reagent (DSF-F), which includes ESAT-6, CFP-10, and Rv3615c, was recently demonstrated in an intradermal DIVA test. The reactive agent showed 90% sensitivity and 95% specificity [ 61 , 110 ]. Although promising under experimental conditions, the performance of this DIVA test under conditions of natural challenge in a field test in different regions is still pending.…”

Differences in skin test reactions to official and defined antigens in guinea pigs exposed to non-tuberculous and tuberculous bacteria

“…Antigenic reagents other than standard PPDs have been developed. Some have the capability to differentiate infected from Bacille Calmette-Guérin (BCG)–vaccinated animals (DIVA) because they are based on regions that are absent or not immunogenic in BCG vaccine strains (ESAT-6, CFP-10 and Rv3615c) 6 , like the defined antigens peptide cocktail long (PCL) and triple fusion protein (FP) used in previous studies 7 , 8 . A protein complex affinity-purified from the PPD-B called P22 has been developed as an alternative antigen in TB antibody based diagnosis 9 .…”