Seroepidemiological Study of Bovine Brucellosis in Tigray Region, Northern Ethiopia
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Date
2005-06
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Abstract
A cross-sectional epidemiological study was carried out from September 2004 to March 2005 to determine the seroprevalence of bovine brucellosis in the intensive and extensive cattle production systems of Tigray Region, to identify the risk factors that contribute to the occurrence of brucellosis and assess the public health significance of the disease.
The study populations were comprised of indigenous and crossbred cattle in the Region and samples were selected by two-stage cluster sampling. Serum samples collected from 1,951 cattle above six months of age, of which 1,135 from the intensive farms and 816 from the extensively managed herds were screened for Brucella antibodies by the Rose Bengal Plate Test (RBPT) and the reactor sera were further tested by the Complement Fixation Test (CFT). Moreover, information was gathered on age, sex, herd size, management, and agro-ecology of each sampled animal to determine the risk factors for brucellosis seropositivity. Likewise, data on farm or herd-level risk factors and other farm characteristics were obtained using a questionnaire survey, which was administered in person to 112 intensive farms and members of animal owners in the 26 extensive herds. Furthermore, in order to assess the zoonotic importance of the disease, 185 human serum samples were also screened for brucellosis.
In this study, the overall seroprevalence of Brucella antibodies in cattle was 1.49%. However, individual animal seroprevalence was found to vary from 0.26% in the intensive farms to 3.19% in animals reared under the extensive management system. Statistically significant difference was observed in seroprevalence values between the intensive and extensive management systems (p<0.05). The overall herd-level prevalence varied from 2.68 % in the intensive farms to 42.31% in the extensively managed herds whereas within-herd prevalence differed from 0% - 33% in the intensive farms to 0% - 11% in the extensive herds based on CFT. However, no antibodies against Brucella were detected in the human sera.
The results of univariate logistic regression analysis revealed that age, herd size and parity number of animals had no statistically significant effect on individual animal seropositivity to brucellosis in the intensive management system. However, in the extensive management system, seropositivity to brucellosis was significantly higher in animals kept under the transhumance management sub-system than animals in the sedentary sub-system (p<0.001). The results also indicated that there was a statistically significant increase in seroprevalence to
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brucellosis with increasing age (p<0.01) but not parity (p>0.05). Significant increment of seropositivity was also observed as herd size increases from small to medium (p<0.05) and then to large sizes (p<0.001). In addition, a significantly higher seroprevalence was found in animals in the lowland than those in the highland agro-climatic zones. Nevertheless, in the multivariate logistic regression analysis, systemic factor (OR = 10.6%, 95% CI = 2.3 – 49.3, p<0.01) and age (OR = 4.2, 95% CI = 2.3 – 49.3, p<0.01) were identified as the major risk factor for individual animal seroprevalence in the extensive management system. Transhumance management sub-system was also significantly associated with increased herd seroprevalence (p<0.01) but not herd size (p>0.05) in the extensive management system. Furthermore, there was a statistically significant association between seropositivity to brucellosis and history of previous abortions (Fisher’s exact p<0.001) and stillbirths (Fisher’s exact p<0.05) in the extensive herds but only of abortion (Fisher’s exact p<0.01) in the intensive farms.
The results of this study showed that brucellosis is an endemic and widely distributed disease in Tigray Region with relatively high seroprevalence in the extensive than the intensively managed cattle. The implementations of better management practices are recommended to prevent further spread of the disease.
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Bovine, brucellosis, seroepidemiology, seroprevalence, Tigray Region