No abstract

Bovine brucellosis is a zoonotic disease spread worldwide. The infection in cattle is predominantly caused by Brucella abortus and is usually detected in pregnant females through abortions. The disease is endemic in Argentina; however, infection in humans is underestimated and often not reported. The prevalence of bovine brucellosis in countries bordering Argentina is quite variable: 0.04% in Uruguay, 10.20% in the north and 0.06% in the south of Brazil, 0.2% in Chile, 3.15% in Paraguay and 2.27% in Bolivia. In 1999, the Argentine National Control and Eradication Program was implemented. Its strategies include identification of vaccinated animals, compulsory vaccination with B. abortus S19 of 100% of 3- to 8-month-old females, negative serological tests before animal movements and categorization of farms in terms of their brucellosis status. The epidemiological surveillance in milk is performed through the milk ring test and the indirect ELISA. The result of a national brucellosis survey performed in 2004 indicates that 12.4% (95% CI: 10.89-14.0) of Argentine beef farms are seropositive to Brucella and that the apparent prevalence in cattle is 2.10% (95% CI: 1.90-2.40). The official serological diagnostic tests are as follows: buffered plate antigen test, as screening, serum agglutination test, 2-mercaptoethanol and fluorescence polarization assay, competitive ELISA, as confirmatory tests, and complement fixation test, as definitive test. Santa Fe and a district in Córdoba have 'Outstanding Plans'. Tierra del Fuego is a 'Zone free from bovine brucellosis'. One question arising when studying the Argentine situation is why the disease remains endemic if good regulations exist to control and eradicate it. In future, some different aspects might be evaluated to understand it, and further studies should be performed to prioritize, select and refine control strategies.

BackgroundBovine brucellosis (BB) is a zoonotic disease caused by Brucella abortus. BB is endemic in Argentina, where vaccination with Brucella abortus strain 19 is compulsory for 3-to-8 month-old heifers. The objectives of this study were to quantify the prevalence of BB and to identify factors associated with its occurrence, along with the spatial distribution of the disease, in the provinces of La Pampa and San Luis. A two-stage random sampling design was used to sample 8,965 cows (3,513 in La Pampa and 5,452 in San Luis) from 451 farms (187 in La Pampa and 264 in San Luis).ResultsCow and herd prevalence were 1.8 % (95 % CI: 1.3–2.2; n = 157) and 19.7 % (95 % CI: 17.0–22.4; n = 89), respectively. Both cow-level and herd-level prevalence in La Pampa (2.4 and 26.0 %, respectively) were significantly higher than in San Luis (1.4 and 15.5 %, respectively). There were not differences between the proportions of reactive cattle compared to that obtained in a survey conducted in 2005. However, herd prevalence in La Pampa was significantly (P < 0.05) higher compared to that study. Disease was found to be spatially clustered in west La Pampa. The lower the bovine density and the calf/cow ratio, the higher odds of belonging to the cluster.ConclusionsThe increase of farm prevalence in the last five years suggests that the disease is spreading and that control measures should be applied in the region.The cluster of infected farms was located in the west region of La Pampa. There, farms have lower animal densities and smaller cow/calf indices compared to the rest of the province. Although western La Pampa has more infected herds, within-farm prevalence was not higher, which suggests that the control program has been relatively successful in controlling the disease at the farm level, and/or that low animal density inherently results in low disease prevalence. Our results provide baseline information on the epidemiology of BB and its potential pattern of transmission in Argentina, which will ultimately help to improve BB control programs in the country.