Spatial risk factors related to outbreaks of contagious bovine pleuropneumonia in northern Italy (1990-1993)

In October 1990, an outbreak of contagious bovine pleuropneumonia (CBPP) was reported in Italy after an absence of approximately one century. Since October 1990, ninety-four outbreaks have occurred in Italy, of which forty-seven were concentrated in three areas of northern Italy (Lombardy region). The disease was eradicated in September 1993. The data used for the analysis were obtained from the epidemiological investigations undertaken during the outbreaks of 1990-1993. The unit of interest for the analysis is the farm. Spatial segregation of infected and uninfected farms within the study area was determined through the Pielou index of segregation. Data from herds within the same set of outbreaks were analysed through logistic regression to identify factors which could be used to discriminate between infected and uninfected herds. The study indicated a clear spatial segregation between infected and uninfected herds. The results of the analysis do not indicate the mode of disease spread. However, the study demonstrated that both aerosol and indirect transmission of the infection could have occurred, as previously documented in Africa. The possibility that indirect transmission played a prominent role in the spread of CBPP in the region of Lombardy is a completely new suggestion. Further studies are required to understand the epidemiology of CBPP in regions with intensive farming and a relatively cold climate. In particular, three aspects require consideration; firstly, animal movement among neighbouring herds could produce a pattern of disease similar to the one produced by indirect transmission (this possibility was excluded in the epidemiological outbreak investigations conducted by field veterinarians). Secondly, the methods of spatial analysis used in this study have not been previously used in the field of veterinary epidemiology. Further validation of the efficacy of these methods is thus required. Thirdly, the epidemiology of CBPP under conditions of high animal density and a relatively cool climate, as encountered in Lombardy, requires further investigation.