ABSTRACT

Leptospirosis is an infectious disease that causes losses of productivity in cattle due to reduction of milk production, reproductive disorders and calf mortality, while also increasing costs associated with veterinary care, vaccines and diagnostic tests. The objective of this study was to analyze serological findings for bovine leptospirosis in the State of Rio Grande do Sul, Brazil, in order to detect temporal trends in the frequency of seropositive animals and to generate hypothesis about the fluctuation in seroprevalence along the period from 1996 to 2006. Simple linear regression and generalized linear models were used to analyze trends and verify factors influencing the frequency of seropositive animals, respectively. During 11 years, 18,806 serum samples were analyzed, in which 9,385 were positive (49.9%). The time-series analysis by serovars revealed a statistically significant increasing trend in the frequency of the following serovars: Australis, Autumnalis, Bratislava, Copenhageni, Grippotyphosa, Pyrogenes and Tarassovi (p < 0.01). Conversely, a statistically significant decreasing trend was observed for the serovars Hardjo and Wolffi (p < 0.01). There was a significant association between rain precipitation (mm) and the number of samples seropositive for leptospirosis (p = 0.01, OR = 1,003).

KEY WORDS
Leptospirosis; generalized linear model; bovine; time-series