Economic analysis of vaccination to control bovine brucellosis in the States of Sao Paulo and Mato Grosso, Brazil.

Brucellosis is a zoonotic disease that causes important economic losses in Brazil, and the country has therefore established a national program for its control and eradication. Using data generated in the last national brucellosis survey, we conducted an economic analysis in two Brazilian States with different brucellosis status, Mato Grosso (with high prevalence) and Sao Paulo (with low prevalence). The economic analysis was based on the calculation of the additional benefits and costs of controlling bovine brucellosis through the vaccination of heifers aged between 3 and 8 months with S19 vaccine, considering maximal and minimal impacts of the disease. The analysis showed that vaccinating 90% of the replacement heifers aged 3-8 months of age offers the best economic performance in a vaccination program against bovine brucellosis if compared to vaccination rates of 70% and 80%. Moreover, regions with higher prevalences of bovine brucellosis would experience significant economic advantages when implementing a vaccination strategy to control the disease. This economic analysis will allow decision makers to plan more economically effective vaccination programs.

Situação epidemiológica da brucelose bovina no Estado da Bahia / Epidemiological situation of bovine brucellosis in the State of Bahia, Brazil

O trabalho consistiu em estratificar o Estado da Bahia em quatro regiões com características homogêneas (circuitos produtores) para que fossem amostradas aleatoriamente, em cada uma delas, 300 propriedades. Em cada propriedade foram escolhidas, de forma aleatória, 10 a 15 fêmeas bovinas adultas, das quais foi obtida uma amostra de sangue. No total, foram amostrados 10.816 animais, provenientes de 1.413 propriedades. O protocolo de testes utilizado foi o da triagem com o teste do antígeno acidificado tamponado (Rosa Bengala) e a confirmação dos positivos com o teste do 2-mercaptoetanol. O rebanho foi considerado positivo se pelo menos um animal reagiu às duas provas sorológicas. As prevalências de focos e a de fêmeas adultas soropositivas do Estado foram de 4,2 por cento [3,1-5,3 por cento] e 0,66 por cento [0,41-0,93 por cento], respectivamente. Para os circuitos produtores foram: circuito 1, 5,8 por cento [3,6-8,7 por cento] e 0,86 por cento [0,41-1,3 por cento]; circuito 2, 3,1 por cento [1,5-5,6 por cento] e 1,2 por cento [0,25-2,1 por cento]; circuito 3, 6,3 por cento [4,0-9,3 por cento] e 1,7 por cento [0,66-2,7 por cento]; e circuito 4, 0,60 por cento [0,07-2,2 por cento] e 0,07 [0,00-0,21 por cento]. Para a análise de fatores de riscos associados à doença foi aplicado um questionário epidemiológico em cada propriedade visitada. Os fatores de risco (odds ratio, OR) associados à condição de foco foram: compra de reprodutores (OR= 2,27) e presença de áreas alagadiças (OR= 1,76). A vacinação de fêmeas de três até oito meses de idade foi um fator de proteção (OR= 0,53).

A study to characterize the epidemiological situation of bovine brucellosis in the State of Bahia was carried out in 2004. The State was divided into four similar production regions, 300 herds were randomly sampled in each region, and 10 to 15 adult bovine females were sampled in each of these herds. A total of 10,816 serum samples from 1,413 herds were collected. The serum samples were screened for antibodies to Brucella spp. by the Rose-Bengal Test (RBT), and all RBT-positive sera were re-tested by the 2-mercaptoethanol test (2-ME) for confirmation. A herd was considered positive if at least one animal was positive on both RBT and 2-ME tests. The prevalence of infected herds and seropositive adult bovine females in Bahia State were: 4.2 percent [3.1-5.3 percent] and 0.66 percent [0.41-0.93 percent], respectively. In the production regions, prevalence of infected herds and animals were, respectively: region 1, 5.8 percent [3.6-8.7 percent] and 0.86 percent [0.41-1.3 percent]; region 2, 3.1 percent [1.5-5.6 percent] and 1.2 percent [0.25-2.1 percent]; region 3, 6.3 percent [4.0-9.3 percent] and 1.7 percent [0.66-2.7 percent]; and region 4, 0.60 percent [0.07-2.2 percent] and 0.07 percent[0.00-0.2 percent]. In each herd, an epidemiological questionnaire was applied. The risk factors (odds ratio, OR) associated with the presence of the infection were: purchase of breeding animals (OR = 2.27) and presence of flood areas (OR= 1.76). Vaccination of heifers from three to eight months of age was a protective factor (OR=0.53).