Anàlisi de risc de la introducció de la diarrea vírica bovina i l'herpesvirus boví 1 en funció de les mesures de bioseguretat aplicades a les granges de vaques de llet

Résumé

The general aim of this PhD thesis was to develop a risk assessment tool to support biosecurity measures prioritization decision making in dairy farms. In the first study, a stochastic risk analysis model was developed to quantify Bovine viral diarrhea virus (BVDV) and Bovine herpesvirus type 1 (BoHV-1) introduction through animal movements. Purchasing cattle, rearing replacement heifers offsite and showing cattle at competitions, were considered in the model. Besides a review of the scientific literature, parameters were estimated using animal movement database, biosecurity surveys and the opinion of field veterinarians. In this model, 46 farms from Galicia and Catalonia that moved animals during 2017 were included. Results showed that the annual probability of BVDV and BoHV-1 introduction was very heterogeneous, being close to 0 in some farms and in others close to 1. The median of the probability of introduction of BVDV was 12% and for BoHV-1 9%, with an inter-quartile range from 1.2% to 28% for BVDV and 3% to 23% for BoHV-1. The highest probabilities were associated with local movements of cattle (i.e., inside the same autonomous community) and the fact of sharing the transport vehicle between farms. By evaluating the effect of biosecurity measures on a selected farm, implementation of a correct quarantine or not sharing transport with other farms greatly decreased this probability. In the second study, the probability of BVDV and BoHV-1 introduction through indirect contacts was quantified also with a stochastic risk analysis model. Vehicles transporting calves, cattle to slaughterhouse, dead animals, and food mix, as well as visits by veterinarians and hoof trimmers, farm workers and contacts with neighbors were considered in the model. For this study were included the 127 farms that participated in the project. Data to estimate model parameters was obtained from the sources indicated before as well as from interviews with hoof trimmers, animal transporters and a rendering company. Results evidenced that the median annual probability of introduction for BVDV was 2.1% and for BoHV-1 3.9%, in a range of 0.5% to 14.6% and 1.0% to 24.9% for BVDV and BoHV-1, respectively. The calf transport vehicle and veterinarians’ visits were the routes with the highest risk. The biosecurity measures with the greatest impact in reducing the probability of introduction of both viruses were the use of boots and clothing belonging to the farm and avoiding the driver that transports cattle coming into contact with the animals on the farm. The two models allowed establishing the riskiest pathways for each studied farm and thus are a useful tool to prioritize biosecurity measures that must be implemented or improved to reduce the probability of BVDV and BoHV-1 introduction into a farm.