Field evaluation of Specific Mycobacterial Proteins-Based Skin Test for
the Differentiation of Mycobacterium bovis-Infected and Bacillus
Calmette Guerin-Vaccinated Crossbred Cattle in Ethiopia
Bovine tuberculosis (bTB) challenges intensive dairy production in
Ethiopia and implementation of the test and slaughter control strategy
is not economically acceptable in the country. Vaccination of cattle
with Bacillus Calmette-Guerin (BCG) could be an important adjunct to
control, which would require a diagnostic test to differentiate
Mycobacterium bovis (M. bovis)-infected and BCG-vaccinated animals (DIVA
role). This study describes evaluation of a DIVA skin test (DST) that is
based on a cocktail (DSTc) or fusion (DSTf) of specific (ESAT-6, CFP-10
and Rv3615c) M. bovis proteins in Zebu-Holstein crossbred cattle in
Ethiopia. The study animals used were 74 calves (35 BCG-vaccinated and
39 unvaccinated) aged less than three weeks at the start and 68 known
bTB positive cows. Six weeks after vaccination, the 74 calves were
tested with DSTc and the single intradermal cervical comparative
tuberculin (SICCT) test. The cows were tested with DSTc and SICCT test.
Reactions to DSTc were not observed in BCG-vaccinated and unvaccinated
calves while SICCT test reactions were detected in vaccinated calves.
DSTc reactions were detected in 95.6% of the cows and single
intradermal tuberculin (SIT) positive reactions were found in 98.2%
(95% confidence interval, CI, 92.1–100%). The sensitivity of DSTc was
95.6% (95% CI, 87.6–99.1%), and significantly (P<0.001)
higher than the sensitivity (75%, 95% CI, 63.0-84.7%) of the SICCT
test at 4mm cutoff. DSTf and DSTc reactions were correlated (r = 0.75;
95% CI =0.53–0.88). In conclusion, DSTc could differentiate M.
bovis-infected from BCG-vaccinated cattle in Ethiopia. DST had higher
sensitivity than the SICCT test. Hence, DSTc could be used as a
diagnostic tool for bTB if BCG vaccination is implemented for the
control of bTB in Ethiopia and other countries.