Infectious diseases in Emilia-Romagna (Italy) dairy farms: ecological modelling and network analysis

Abstract

Studying the spread of infectious diseases at the humans-domestic animals-wild animals interface is fundamental in order to preserve all three named compartments health. In particular, infection in livestock produced several impacts during the last two decades, threatening the sustainability of farming in different areas all over the world. The focus of this thesis is to disentangle the potential pathogens spread through farming systems, using ecological modelling methods. I worked on the dairy cattle system in the Emilia-Romagna (ER) region and in the Province of Parma (Italy). In the first chapter I reviewed the published models for bovine tuberculosis (bTB), a very dangerous disease for both cattle and humans health worldwide. In particular, I focused on the understanding of models structure and assumptions. In the second chapter, I evaluated the performance of bTB surveillance system in the ER system, a bTB-free region since 2007. The surveillance system is composed by three detection methods: on-farm routine skin-testing, exchanged cattle skin-testing, and slaughterhouse carcass inspection. In order to evaluate their performances, I built a stochastic network model, able to represent both within-farm and between-farm bTB dynamics, and calibrated on available data on ER dairy farms. The surveillance system was assessed through the comparative analysis of a number of statistics, including the time required for epidemic detection and the total number of infected farms during the epidemic. Results showed that slaughterhouse inspection and on-farm routine surveillance mainly contributed both to the surveillance system effectiveness, while exchanged cattle testing was relatively marginal. In the third chapter of my thesis, I analysed the indirect contacts existing between farms. These contacts are due to fomites mediated infections between farms, caused by farm-visitors moving between farms. In my case of study I analysed: private and government veterinarians, and milk trucks. My results showed that all three indirect contacts networks considered was very different in respect to direct one, and that they created an higher number of between-farm connections in respect to cattle movements. This suggested that the indirect contact route of transmission should not be neglected in control and surveillance effective strategies for highly contagious diseases.