Spatial-temporal cluster analysis of fatal Clostridium chauvoei cases among cattle in Styria, Austria between 1986 and 2013.

Clostridium chauvoei is a gram positive, spore building bacterium that causes blackleg, a mostly fatal disease in cattle and other ruminants. Although the disease is common, little is known on the epidemiology of blackleg. As infection occurs through the environment, the risk of blackleg might be increased in areas with a specific climate or soil type. Therefore, the objective of the present study was to identify spatial and temporal clusters in the incidence of blackleg in the province of Styria, Austria. Data were collected within the governmentally delivered blackleg control program which includes vaccination of cattle with access to known blackleg pastures and compensation for fallen stock. Between 1986 and 2013, 1448 suspect blackleg cases were reported to official veterinarians; with blackleg confirmed through bacteriology in 266 cases (18%). The number of confirmed blackleg cases was highest in 2011 (25 cases) and lowest in 2004 (2 cases). Mean annual blackleg incidences varied considerably between different municipalities from 0 cases in most of the Southern parts of the province to 584 cases/1,000,000 cattle in some Northwestern municipalities. The spatio-temporal analysis identified one high risk cluster in the Northwest where cattle had 9.56 times the risk to develop blackleg compared to those in Northern and Northeastern parts of the province. Furthermore, a low-risk cluster was identified in the southeastern part of the province, where cattle had a relative risk of 0.015 to die of blackleg. No temporal or spatio-temporal clusters were identified. Results of the present study suggest that blackleg cases are clustered within certain geographic areas which might be due to soil type and water permeability. Results of this study should be used to motivate farmers to vaccinate cattle against Clostridium chauvoei in known areas with high risk.