Abstract
Brucellosis is an important zoonotic disease that affects animal and human health worldwide, particularly in developing countries including Pakistan. Punjab is the most populous province having about 50% of the human and animal population of the country. In Punjab, dense animal and human populations, smallholder farming systems, poor husbandry practices, and lack of vaccination and animal movement control are important factors that have increased the risk of transmission of the disease. Hence, the government has launched a brucellosis control program to reduce the spread of bovine brucellosis using an active surveillance approach. This large-scale population-based study under the brucellosis control program aimed to i) estimate the seroprevalence, ii) identify important risk factors and iii) provide the spatial distribution of bovine brucellosis in Punjab province of Pakistan. In this study, 12,406 livestock farms/holdings in 34 districts having 61,084 animals (31,307 cattle and 29,777 buffaloes) were georeferenced and screened for Brucella antibodies between July 2020 and June 2021 through an intensive network of laboratories under the directorate of Animal Disease Diagnostic, Reporting and Surveillance, Punjab. The sera were initially tested by Rose Bengal Plate Test and the positive samples were confirmed with Indirect Enzyme-linked Immunosorbent Assay. Data on various farm and animal-level risk factors was also collected and analyzed through multivariable mixed models. The overall animal-level seroprevalence was 0.84% (514/61,084), while the herd-level prevalence was 3.13% (389/12,406). Within-herd prevalence ranged from 0 to 100%. The prevalence was higher in the north-eastern part of the province with the highest in Hafizabad district [herd prevalence: 45.21% (95%CI: 39.88 – 50.64%), animal prevalence: 16.83% (95%CI: 14.49 – 19.38%)], followed by Gujranwala [herd prevalence: 22.17% (95%CI: 16.65 – 28.51%), animal prevalence: 7.47% (95%CI: 5.86 – 9.36%)], while in 14 districts no seropositive animal was detected. The spatial analysis identified significant clustering in the northeastern part of the province. The chances of Brucella infection were 1.70 times higher in females (P=0.029, 95% CI: 1.36-1.92) than in male animals. Every one-year increase in age increased the odds of being Brucella positive by 1.26 times (P <0.001, 95% CI: 1.22-1.30). The analysis of herd-level factors revealed that the odds of occurrence of brucellosis were 2.98 times on farms that had an abortion history (P<0.001). Similarly, farms with free stall housing (OR=3.01, P<0.001), animal purchase history during the last year (OR=1.35, P<0.001) and artificial insemination practice (OR=1.35, P<0.001) had also higher odds of occurrence of Brucella infection. In conclusion, the study provides a detailed insight into the epidemiology of bovine brucellosis in Punjab that will help to develop more targeted interventions for the control of brucellosis leading to better animal and human health.