Pathology of Bovine Tuberculosis in Three Breeds of Dairy Cattle and Spoligotyping of the Causative Mycobacteria in Ethiopia.

Mulualem Ambaw,Gobena Ameni,Adane Worku,Aboma Zewude,Aster Yohannis,Benti Deresa Gelalcha,Berecha Bayissa

doi:10.3389/fvets.2021.715598

Abstract

Different breeds of cattle were observed to have a variable degree of susceptibility to bovine tuberculosis (bTB). The screening of bTB was conducted on 720 dairy cattle consisting of three breeds using the single intradermal cervical comparative tuberculin (SICCT) test. Besides this, 43 SICCT test-positive cattle were used to compare the severity of the pathology of bTB among the three breeds and to identify the causative mycobacteria using spoligotyping. The overall SICCT test positivity was 17.92% (129/720) by pooling all animals in the three farms. There was a significant difference in SICCT test positivity among the three breeds (χ2 = 71.06; p < 0.001); the highest (25.34%) was recorded in the crossbreed followed by the Boran breed (10.08%), while the least (3.14%) was recorded in the Jersey breed. On other hand, the highest median pathology score (10.0, interquartile range, IQR = 6.0–17.0) was recorded in Boran followed by cross (5.0, IQR = 3.5–7.5), while the least (3.0, IQR = 2.25–3.0) was recorded in Jersey. Thus, the difference in the median pathology scores was significant [Kruskal Wallis = 18.78, p < 0.001] among the three breeds. Furthermore, multivariate analysis using ordinal logistic regression by considering age, sex, breed, reproductive status, and location of the farms also showed a significant [ = 11.97, p < 0.01] difference in pathology scores among the three breeds of cattle. Even at a single-herd level at Holeta, the difference in severity of pathology between the Boran and crossbreeds was significant (U = 33.5; p < 0.01). Culture positivity was 39% in 108 suspicious tissues. Fourteen Mycobacterium bovis (M. bovis) and two Mycobacterium tuberculosis (M. tuberculosis) were isolated from the lesions. All the 14 M. bovis isolates belonged to SB0912, while the two M. tuberculosis belonged to SIT54. In conclusion, although the frequency of the SICCT test positivity was high in the crossbreed, a more severe pathology was observed on the Boran (zebu) breed. In addition M. tuberculosis was isolated from TB lesions of dairy cattle, demonstrating the role of M. tuberculosis in causing TB in cattle.

Highlights

Bovine tuberculosis is a chronic infectious disease of cattle and is characterized by the formation of tubercles in the lungs, lymph nodes, intestine, kidney, and other tissues [1]. bTB is primarily caused by Mycobacterium bovis (M. bovis), the other members of Mycobacterium tuberculosis complex (MTBC) have been reported to cause bTB [2]
When individual farms are considered, the SICCT test positivity were 27.2% (31/114), 25.41% (92/362), and 2.26% (6/244) in the farms located at Bishoftu, Holeta, and Adaberga, respectively
There was a significant difference in SICCT test positivity among the three breeds (χ 2 = 71.06; p < 0.001); the highest SICCT test positivity (25.34%) was recorded in the crossbreed, followed by the Boran breed (10.08%), while the least (3.14%) was recorded in the Jersey breed

Summary

Introduction

Bovine tuberculosis (bTB) is a chronic infectious disease of cattle and is characterized by the formation of tubercles in the lungs, lymph nodes, intestine, kidney, and other tissues [1]. bTB is primarily caused by Mycobacterium bovis (M. bovis), the other members of Mycobacterium tuberculosis complex (MTBC) have been reported to cause bTB [2]. M. bovis is most frequently isolated from cattle and less frequently from several other animals, including humans [2, 3]. On the other hand M. tuberculosis is primarily adapted to human beings, though it is occasionally isolated from other mammals [2]. Both M. bovis and M. tuberculosis belong to MTBC, which consist of mycobacterial species exhibiting a 99.9% sequence similarity with conserved 16SrRNA, with the exception of M. canetti [4], and are capable of causing a serious disease with a similar pathology [5]. The disease is transmitted to humans, causing zoonotic TB in about 15% of the human population in developing countries [11]

Methods

Results

Conclusion