Assessing the feasibility of test-and-cull and test-and-segregation approaches for the control of high-prevalence bovine tuberculosis in Ethiopian intensive dairy farms.

Bovine tuberculosis (bTB) is endemic and has a substantial impact on the livestock sector in Ethiopia and other low and middle-income countries (LMICs). With a national emphasis on dairy farm intensification to boost milk production and spur economic growth, the incidence of bTB is anticipated to rise. However, Ethiopia, like other LMICs, lacks a comprehensive national bTB control strategy due to the economic and social infeasibility of traditional test-and-cull (TC) approaches. To inform the development of such a strategy, we evaluated the effectiveness and feasibility of TC and test-and-segregation (TSg) strategies for bTB control on Ethiopian dairy farms. A TC approach was used at Farm A [N = 62; comparative cervical test (CCT) > 4 mm, starting prevalence 11.3%] while TSg was implemented at Farm B (N = 45; CCT > 4 mm, prevalence 22.2%), with testing intervals of 2-4 months. Both strategies achieved a reduction in bTB prevalence to 0%, requiring seven rounds of TC over 18 months at Farm A, and five rounds of TSg over 12 months at Farm B's negative herd. The results show that adopting more sensitive thresholds [CCT > 0 mm or single cervical test (SCT) > 2 mm] during later rounds was pivotal in identifying and managing previously undetected infections, emphasizing the critical need for optimized diagnostic thresholds. Cost analysis revealed that TC was approximately twice as expensive as TSg, primarily due to testing, labor, and cow losses in TC, versus construction of new facilities and additional labor for TSg. This underscores the economic and logistical challenges of bTB management in resource-limited settings. Taken together, our study highlights an urgent need for the exploration of alternative approaches including TSg and or vaccination to mitigate within herd transmission and enable implementation of bTB control in regions where TC is not feasible.

BCG vaccination reduces bovine tuberculosis transmission, improving prospects for elimination.

Bacillus Calmette-Guérin (BCG) is a routinely used vaccine for protecting children against Mycobacterium tuberculosis that comprises attenuated Mycobacterium bovis. BCG can also be used to protect livestock against M. bovis; however, its effectiveness has not been quantified for this use. We performed a natural transmission experiment to directly estimate the rate of transmission to and from vaccinated and unvaccinated calves over a 1-year exposure period. The results show a higher indirect efficacy of BCG to reduce transmission from vaccinated animals that subsequently become infected [74%; 95% credible interval (CrI): 46 to 98%] compared with direct protection against infection (58%; 95% CrI: 34 to 73%) and an estimated total efficacy of 89% (95% CrI: 74 to 96%). A mechanistic transmission model of bovine tuberculosis (bTB) spread within the Ethiopian dairy sector was developed and showed how the prospects for elimination may be enabled by routine BCG vaccination of cattle.

A defined antigen skin test for the diagnosis of bovine tuberculosis.

Bovine tuberculosis (bTB) is a major zoonotic disease of cattle that is endemic in much of the world, limiting livestock productivity and representing a global public health threat. Because the standard tuberculin skin test precludes implementation of Bacille Calmette-Guérin (BCG) vaccine-based control programs, we here developed and evaluated a novel peptide-based defined antigen skin test (DST) to diagnose bTB and to differentiate infected from vaccinated animals (DIVA). The results, in laboratory assays and in experimentally or naturally infected animals, demonstrate that the peptide-based DST provides DIVA capability and equal or superior performance over the extant standard tuberculin surveillance test. Together with the ease of chemical synthesis, quality control, and lower burden for regulatory approval compared with recombinant antigens, the results of our studies show that the DST considerably improves a century-old standard and enables the development and implementation of critically needed surveillance and vaccination programs to accelerate bTB control.