Pathology of camel tuberculosis and molecular characterization of its causative agents in pastoral regions of Ethiopia

Abstract

A cross sectional study was conducted on 906 apparently healthy camels slaughtered at Akaki and Metehara abattoirs to investigate the pathology of camel tuberculosis (TB) and characterize its causative agents using postmortem examination, mycobacteriological culturing, and multiplex polymerase chain reaction (PCR), region of difference-4 (RD4)-based PCR and spoligotyping. The prevalence of camel TB was 10.04% (91/906) on the basis of pathology and it was significantly higher in females (χ(2) = 4.789; P = 0.029). The tropism of TB lesions was significantly different among the lymph nodes (χ(2) = 22.697; P = 0.002) and lung lobes (χ(2) = 17.901; P = 0.006). Mycobacterial growth was observed in 34% (31/91) of camels with grossly suspicious TB lesions. Upon further molecular characterization using multiplex PCR, 68% (21/31) of the colonies showed a positive signal for the genus Mycobacterium, of which two were confirmed Mycobacterium bovis (M. bovis) by RD4 deletion typing. Further characterization of the two M. bovis at strains level revealed that one of the strains was SB0133 while the other strain was new and had not been reported to the M. bovis database prior to this study. Hence, it has now been reported to the database, and designated as SB1953. In conclusion, the results of the present study have shown that the majority of camel TB lesions are caused by mycobacteria other than Mycobacterium tuberculosis complex. And hence further identification and characterization of these species would be useful towards the efforts made to control TB in camels.

Figure 1. Tuberculous lesions from camels on different organs.

(A1) Disseminated and distinct tuberculous lesions in mediastinal parts of the lung. (A2) Tuberculous lesion in mediastinal lymph node and nodules on other parts as indicated by arrows. (A3) Tuberculous lesions in hepatic lymph node. The arrows show that pea-sized lesions throughout the lymph node. (B) Tuberculous lesion in mesenteric lymph nodes as indicated by arrow.

Figure 2. Proportion of mycobacterial culture positivity of the lymph nodes and lungs of TB suspected camels.

Figure 3. Gel electrophoresis separation of PCR products by multiplex PCR genus typing of mycobacteria isolated from naturally infected camels.

Lane 1 = 100bp DNA Ladder; Lane 2 = Mycobacterium avium complex (positive control), Lane 3 = Qiagen H₂O (negative control), Lane 4 = Mycobacterium tuberculosis complex (positive control), Lanes 5–34 were isolates from individual camels with tuberculous lesions. Lane 7 (sample 63), Lane 8 (sample 62) were positive for Mycobacterium tuberculosis complex and Lane 5, 6, 7, 8, 9, 11, 12–13, 15–22, 25, 28, 29, 34 were positive for genus Mycobacterium, Lane 10, 14, 23, 24, 26, 27, 30–33 were negative for genus Mycobacterium.

Figure 4. Gel electrophoresis separation of PCR products by RD4 deletion typing of mycobacteria isolated from naturally infected camels.

Lane 1 = 100bp DNA ladder, Lane 2 = M. tuberculosis positive control, Lane 3 = Qiagen H₂O (negative control), Lane 4 = M. bovis positive control, Lane 5–7 were isolates from camel, Lane 6 and 7 were positive for M. bovis.

Figure 5. Schematic representation of the spoligotyping patterns of isolates of Mycobacterium bovis from camels with tuberculous lesions.

A = M.bovis SB1176 (positive control); B = Qiagen H₂O (negative control); C = M. tuberculosis (positive control); D = sample 63 (SB1953-New strain); E = sample 62 (SB0133). The black rectangles represent positive signals, and the white rectangles indicate negative signals.