Prevalence and risk factors of Brucellosis in Commercial Cattle farms in Lusaka Province.

Abstract

A cross-sectional study was conducted in Lusaka Province of Zambia to estimate brucellosis seroprevalence and identify associated risk factors. This study was done between January 2007 and February 2008 in commercial cattle farms in 3 districts of Lusaka Province (Kafue, Chongwe and Lusaka districts) and one district in Central Province(Chibombo). Sera were collected from animals randomly selected from sampling herds and at the same time data such as sex, age and parity were also recorded. The collected sera were screened for Brucella antibodies using the Rose Bengal test (RBT) followed by confirmation on Competitive Enzyme Linked immunosorbent Assay (C-ELISA). Results were interpreted both in series and parallel. The risk factor identification was done using a pre-tested questionnaire which was administered simultaneously with the blood sampling. The factors assessed included types of cattle breeds, farm ownership, care responsibilities, marketing, feeding practices, herd size, stock density, disease control and proximity to other herds. Prevalence estimates, including the 95% confidence interval, were determined for each district and also for Lusaka province as a whole. The Fisher’s exact test was used to test for associations between Brucella positivity on the farm and the hypothesised risk factors.

A total of 897 serum samples from Lusaka province (n=849) and Chibombo district (n=48) were screened. The estimated overall seroprevalence in Lusaka province was 9.4% (95% CI: 5.0% to 13.6%) while that for Chibombo district was 18.7% (95% CI: 7.5% to 29.9%) based on serial interpretation. The overall herd level prevalence for Lusaka Province was 40.6% (95% CI: 16.4% to 67.9 %) while that for Chibombo was 100%. The prevalences according to sex were oxen 0%; cows 8.1% (95% CI: 4.6% to 11.6%) and bulls 12.5% (95% CI: 3.8% to 21.1%). Prevalences according to age groups were 1 to 4 years 10.7% (95% CI: 4.9% to 16.9%); 4.5 to 5 years 4.2 % (95% CI: 0.0 to 7.8%); 5.5 to 7 years 6% (95% CI: 2.0% to 9.9%) and more than 7 years 9.9% (95% CI: 2.3% to 17.5%). At the animal level, seroprevalence varied according to sex with bulls having slightly higher odds of being seropositive (OR=1.7) compared to females, according to age groups, with the age category 1 to 4 years recording the highest seroprevalence. Chongwe district had a significantly higher prevalence (p < 0.001) than all the other districts in Lusaka province.

A univariate analysis of risk factors showed that the method of acquiring a farm was the most important risk factor. However, other factor such as source of animals was significant at 95% confidence level. The study therefore highlights the need for effective control measures to be put in place to reduce the observed brucellosis prevalences