Structuring the passive surveillance network improves epizootic detection and control efficacy: a simulation study on foot-and-mouth disease in France.

Rapid detection of infection is critical to the containment and control of contagious pathogens. Passive surveillance, based on the detection of clinical signs through farmers' observations and subsequent veterinarian notification, is the primary means of initially detecting an epizootic and for implementing control measures. The objective of this study was to analyse how the composition and structure of passive surveillance networks may impact epizootic spread and control. Three compositions of passive surveillance network were considered: (i) A veterinarian-based surveillance network composed of farmers and veterinarians (the common passive surveillance network where each veterinarian follows up a group of holdings), (ii) a farmer-based surveillance network composed of farmers only (the farmer plays the same role as in the preceding network as well as that of the veterinarian but his point of view is limited to his animals) and (iii) a hierarchical surveillance network composed of farmers, veterinarians and district-level veterinarian specialists (in case of doubt, the local veterinarian calls the specialist veterinarian). We compared the efficacy of these different network types where actors have successively a structurally wider perspective than the preceding ones using a specific stochastic model for the spread of foot-and-mouth disease (FMD). The model was forced by actual data to generate realistic simulated FMD epizootics in France. Our results show that maintaining the presence of field veterinarians following-up several holdings in breeding areas is fundamental and adding veterinarian specialists to passive surveillance networks could greatly enhance surveillance network efficacy.