Bovine brucellosis in Argentina: current situation and intraherd simulation model

Bovine brucellosis is an infectious disease, which can negatively affect cattle productivity and human health. It is endemic in Argentina, where 0.8% of cattle and 12% of farms are infected, having this percentages remained stable throughout the years.
This thesis studies the disease in the country.
At first a review on the Argentine situation is presented, which leads to two remarkable aspects: brucellosis remains endemic and it is not possible to reach its eradication.
In order to to clarify those points, four main studies were performed.
The study 1 is an analysis of cattle movement that showed that there are some districts potential spreaders of the disease while others have more at risk of introduction.
The study 2 constitutes an estimation of the brucellosis prevalence and identification of the risk factors associated with an increased occurrence, which helps to improve the knowledge of the epidemiology of the disease in the country. When assessing the situation at the provinces under study, a spatial cluster of infected farms was detected. In that region, farms are considerably large, having lowanimal densities and few movements. Those factors probably correlate with infrequent veterinary control and poor sanitary conditions of the herds. Special attention should be paid to those zones sharing these characteristics since there is high chance of finding clusters of the disease.
In the study 3 a method for evaluating some farmers' and veterinarians' management practices in relation to brucellosis and for assessing the vaccination campaign and coverage is developed. It shows that the vaccination campaign is globally well implemented, but the immunization coverage and some management practices should be improved.
Finally, the study 4 develops an intra herd simulation model. Its aim is to predict the effects of the disease and to test different control and eradication strategies in different situations. As brucellosis is a contagious disease, when introducing one infected animal in a free herd, it might become endemic. In the case of endemic farms that do not eliminate the reactors, all the tested vaccination strategies produce a reduction in the disease outputs (abortions, infectious deliveries, new infected and born infected) whereas when no vaccination is applied, the outputs remain stable. The isolation of heifers from the general herd reduces the disease outputs by a half. Despite it, if the reactors are not eliminated the sources of infection are kept in the herd. Therefore, a strategy of elimination of infected animals has to be applied. Independently from the chosen vaccination strategy, applying serological tests of high sensitivity and specificity with immediate elimination of reactors produces a dramatic reduction in the disease prevalence. These results might explain the fact that the disease keeps on being endemic in Argentina. Since for achieving eradication at country level, other measures additional to vaccination have to be applied, the mandatory elimination of infected cattle could be taken into account.
Summarizing all these issues, it can be concluded that, although there are good regulations to control and eradicate bovine brucellosis in Argentina. The prevalence is not so high and stable throughout the years and, some improvements have to be made in order to achieve eradication. This thesis attempted to assess the Argentine current situation and to provide tools for policy makers and farmers to obtain that goal.