Seroprevalence Study of Brucellosis in Cattle and Human in Bahirdar Milkshed
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2005-06
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Abstract
A cross-sectional study was conducted in South Gondar, West Gojjam and Awi zones of Amhara Regional State, between October 2004 and March 2005, to determine the sero-prevalence of brucellosis in cattle and humans as well as to identify the likely potential risk factors. Two stage cluster-sampling was employed, by which 11 towns are identified as primary units and 195 farms as secondary units in semi-intensive production system. Similarly, 29 Peasant Associations as primary units and 145 individual cattle owners as secondary units were selected for the extensive production system. In the government cattle breeding ranch all eligible cattle were sampled. Human risk groups were sampled using purposive sampling method. The study methods involved collection serum sample, data, questionnaire surveys and serological tests conducted in laboratories. Accordingly, 1944 cattle (341 clusters in the three production systems) were sampled. The sampling involved all cattle above 6 months of age with no history of previous vaccination against brucellosis. The number of cattle sampled in extensive, semi-intensive and ranch were 864, 754 and 326, respectively. The types of tests used to detect the presence of Brucella antibodies were Rose Bengal Plate Test (RBPT) as screening test, and Complement Fixation Test (CFT) as confirmatory test. Results of the two tests were interpreted serially. A cluster was said to be positive if at least one animal reacts positively by both RBPT and CFT.
The overall individual and cluster level sero-prevalence of cattle in the extensive, semi-intensive and ranch were 4.63 % (n=90) and 14.96 % (n=51), respectively. The within cluster sero- prevalence varied between 0% and 100%, with an overall mean (±SD) of 24.27% (±17.68). For semi-intensive production system, the sero-prevalence varied between 0% and 100% the mean (+SD) sero- prevalence was 26.82 % (±22.52), and in the extensive production system the within cluster sero-prevalence varied between 0% and 50% and an average (+SD) sero- prevalence of 25.44% (±10.45).
There was a highly significant difference in sero-prevalence to Brucella antibody among Awi, West Gojjam, South Gondar at both individual level (p=0.000) and cluster level (p=0.000). However, Awi and West Gojjam zones did not vary significantly at both individual and cluster
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levels. In the midland and highland Brucella sero-reactor varied significantly at both individual level (p=0.000) and cluster level (p=0.000), respectively. Apparently there was no significant difference among the ranch, extensive and semi-intensive production systems, at both individual and cluster levels (p=0.082) and (p=0.255), respectively.
Sero-reactor female and male were found to vary significantly in the semi-intensive production (p=0.042) as opposed to extensive (p=0.115) and ranch (p=0.50). Generally, females were found more affected. Significant difference in sero- prevalence to Brucella antibody among age groups (0.5-1,>1- 3, >3 years) was observed in the semi-intensive production (p=0.001), yet in extensive production and ranch the variation was not significant. Virtually, the sero-porevalences of the three herd categories having < 5 cattle, 5- 10 cattle and those with > 10 cattle were found significantly different in semi-intensive production (p=0.000); however, herd size had not been crucially important in extensive production. Our current finding revealed no significant variation between the two breeds of cattle, Fogera (indigenous zebu) and cross bred (Fogera X Friesian).
Abortion and retained fetal membrane were found to be significantly related to brucellosis in the semi-intensive production (p=0.021) and (p=0.001), respectively; however, the two clinical signs were not found significantly associated in the extensive production. None of the management and husbandry related factors from the questionnaires were found significantly associated with sero-positivity, though a few of them had some association.
Of the total 238 human serum samples tested, 3.78% (n=9) sera were found positive; both sexes were almost equally affected. Although not statistical significant, middle and old age groups were more affected than younger ones. In conclusion, the present study revealed a wider distribution of sero-reactor cattle in the study area; similarly the zoonotic importance of the disease was established, hence warranting future detailed study in the area.
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Sero-prevalence, sero-reactor, sero-positive, semi-intensve, extensive