EPIDEMIOLOGY OF TUBERCULOSIS IN CAMELS SLAUGHTERED AT AKAKI ABATTOIR, CENTRAL ETHIOPIA
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2017-06
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Abstract
Camels are important sources of milk and meat for the pastoral communities of East Africa as they are adapted to the harsh environment in this region. However, these animals are facing different health constraints including tuberculosis (TB). TB can also be transmitted to pastoralists from camels since their milk is consumed raw and as the pastoralists live in close physical contact with potentially infected camels. However, little data is available on the epidemiology of TB in camels in this region. In addition, the diagnostic performance of the single intra-dermal comparative cervical tuberculin test (SICCT) for diagnosis of TB in camels has not been evaluated in Ethiopia. This study was undertaken between February, 2014 and July, 2016 to investigate the epidemiology of TB and to evaluate the performance of SICCT in camels slaughtered at Akaki abattoir, central Ethiopia. In order to achieve these objectives, a cross-sectional study design was used to recruit 2070 camels for epidemiological studies while the evaluation of SICCT was conducted on 168 camels. Gross pathology was used as a gold standard to define the disease status of each camel. Methodologically, SICCT, post mortem examination, bacteriological culturing and molecular typing were employed.
The prevalence of TB in camels slaughtered at Akaki Abattoir was 7.54% (95%CI: 6.45% -8.7%). Statistically significant association (χ2=26.2, p=0.000) was observed between body condition of the camels and lesion prevalence of TB. However, no significant association (p>0.05) was observed between prevalence and either age, sex, or origin of the camels. Multivariate logistic regression analysis revealed that poor body condition was significantly associated [p= 0.000, (Adjusted OR=2.55, 95%CI: 1.743 - 3.734)] as a risk factor for TB in camels. Relatively higher frequency of lesion was detected in female, poor body conditioned, and Borena camels with a proportion of 87.2%, 46.2%, and 84%, respectively. Anatomically, lesion was frequently found in the sub-mandilbular (54.8%) and retro-pharyngeal (16.94%) lymph nodes. Moreover, severe lesion was observed in sub-mandibular (2.47±0.24), retro-pharyngeal (0.35±0.2) and trachea-broncheal (0.35±0.2) lymph nodes. The result of the validation of SICCT showed that at the cut-off value of ≥3mm, the SICCT had optimum performance. At this cut-off value, the sensitivity and specificity of SICCT were 60.7% and 85%, respectively. Moreover, at a cut-off value ≥3mm, the receiver operating characteristics (ROC) analysis revealed that area under the ROC curve was 0.729 (0.615-0.842) which was statistically significant (p=0.000) for sensitivity and specificity evaluation.
Of the total 168 camels tissues cultured, 36 camels tissues were culture positive for mycobacteria with the isolation rate of 21.4% (36/168). A total of 80 isolates were harvested from the different lymph node tissues of 36 culture positive camels. Identification of the isolates using multiplex polymerase chain reaction (PCR) revealed that 48.8% (39/80) were members of the Mycobacterium tuberculosis complex (MTBC) while the rest were non-tuberculous mycobacteria (NTM). Spoligotyping of the 39 isolates indicated that majority of the isolates (94.9%) identified as orphan strains with no shared spoligotype international type (SIT) in the Spoligotype database while two isolates were identified as SIT-1088 and SIT-118. The lineage of the strains based on Conformal Bayesian Network (CBN) analysis revealed that the dominant lineages were Euro-American (84.6%) and Indo-Oceanic (12.8%) lineages while only one strain was identified as M. africanum lineage (2.6%). The result of the present study suggested the use of ≥3mm cutoff point for the SICCT to diagnose TB in dromedary camels of Ethiopia. Strains of M. tuberculosis identified in camels in the present study could help to elucidate the potential role of camels in the epidemiology of tuberculosis in humans and warrants further investigation as to the transmission dynamics of the disease between pastoralists and their camels which would be helpful to design disease control programs.
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PhD Thesis
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Akaki abattoir, central Ethiopia, comparative tuberculin test, gross pathology