Utility of the Intradermal Skin Test in a Test-and-Cull Approach to Control Bovine Tuberculosis: A Pilot Study in Ethiopia

Matios Lakew; Sreenidhi Srinivasan; Beruhtesfa Mesele; Abebe Olani; Tafesse Koran; Biniam Tadesse; Getnet Abie Mekonnen; Gizat Almaw; Temertu Sahlu; Bekele Seyoum; Kebede Beyecha; Balako Gumi; Gobena Ameni; Hagos Ashenafi; Douwe Bakker; Vivek Kapur; Solomon Gebre

doi:10.3389/fvets.2022.823365

Utility of the Intradermal Skin Test in a Test-and-Cull Approach to Control Bovine Tuberculosis: A Pilot Study in Ethiopia

Front Vet Sci. 2022 Mar 7:9:823365. doi: 10.3389/fvets.2022.823365. eCollection 2022.

Authors

Matios Lakew^{1

2}, Sreenidhi Srinivasan³, Beruhtesfa Mesele⁴, Abebe Olani¹, Tafesse Koran¹, Biniam Tadesse¹, Getnet Abie Mekonnen¹, Gizat Almaw¹, Temertu Sahlu⁴, Bekele Seyoum⁴, Kebede Beyecha⁴, Balako Gumi², Gobena Ameni^{2

5}, Hagos Ashenafi², Douwe Bakker⁶, Vivek Kapur^{3

7}, Solomon Gebre¹

Affiliations

¹ National Animal Health Diagnostic and Investigation Center, Sebeta, Ethiopia.
² Aklilu Lemma Institute of Pathobiology, Addis Ababa University, Addis Ababa, Ethiopia.
³ Huck Institutes of the Life Sciences, The Pennsylvania State University, University Park, PA, United States.
⁴ Alage Agricultural Technical and Vocational Education Training (ATVET) College, Alage, Ethiopia.
⁵ Department of Veterinary Medicine, College of Agriculture and Veterinary Medicine, United Arab Emirates University, Al Ain, United Arab Emirates.
⁶ Independent Researcher and Technical Consultant, Lelystad, Netherlands.
⁷ Department of Animal Science, The Pennsylvania State University, University Park, PA, United States.

Abstract

Bovine tuberculosis (bTB) is one of the top three, high-priority, livestock diseases in Ethiopia and hence, the need for evaluation of potential control strategies is critical. Here, we applied the test-and-segregate followed by cull strategy for the control of bTB in the intensive Alage dairy farm in Ethiopia. All cattle reared on this farm were repeatedly skin tested using the Comparative Cervical Tuberculin (CCT) test for a total of five times between 2015 and 2021. During the first (October 2015) and second (March 2017) rounds of testing, all reactor animals (>4 mm) were culled, while those that were deemed as inconclusive (1-4 mm) were segregated and retested. At retest, animals with CCT >2 mm were removed from the herd. In the third (December 2017) and fourth (June 2018) rounds of tuberculin testing, a more stringent approach was taken wherein all reactors per the severe mode of CCT test interpretation (>2 mm) were culled. A final herd status check was performed in May 2021. In summary, the number of CCT positives (>4 mm) in the farm dropped from 23.1% (31/134) in October 2015 to 0% in December 2017 and remained 0% until May 2021. In contrast, the number of Single Cervical Tuberculin (SCT) test positives (≥4 mm) increased from 1.8 to 9.5% (from 2017 to 2021), indicating that CCT test might not be sufficient to effectively clear the herd of bTB. However, a more stringent approach would result in a drastic increase in the number of false positives. The total cost of the bTB control effort in this farm holding 134-200 cattle at any given time was conservatively estimated to be ~US$48,000. This, together with the need for culling an unacceptably high number of animals based on skin test status, makes the test-and-cull strategy impractical for nationwide implementation in Ethiopia and other low- and middle-income countries (LMICs) where the infection is endemic. Hence, there is an increased emphasis on the need to explore alternate, affordable measures such as vaccination alongside accurate diagnostics to help control bTB in endemic settings.

Keywords: Ethiopia; bovine tuberculosis; control program; prevalence; test and cull.