Clara Marcé

Abstract :

Paratuberculosis is a worldwide incurable disease of ruminants resulting in a decrease in milk production and slaughter value. The aim of this thesis was to evaluate the epidemiological and economic effectiveness of selected paratuberculosis control programmes in infected dairy herds. A stochastic simulation model has been developed to represent both the population dynamics within a dairy herd and the indirect transmission of Mycobacterium avium subsp. paratuberculosis (Map). It has been coupled to an existing bioeconomic model. The spontaneous within-herd progression of
Map infection after the introduction of one infected cattle in an initially susceptible herd was studied in the absence of control measure. The effect of within-herd contacts on Map spread in a persistently infected herd was investigated. The cost-effectiveness of test-and-cull strategies to control Map infection in dairy herds was assessed. Simulation outcomes put forward that, even when no control measure is implemented, fadeout can occur if less than two clinically affected animals are present. In persistently infected herds, the two main transmission routes are transmission via the environment of the farm and in utero transmission. Isolating calves from their herd mates during the first weeks of age has no significant impact on Map transmission. Limiting or delaying calf exposure to adults and early culling of clinically affected adults are thus recommended
to decrease Map prevalence in infected dairy herds. Depending on the targeted objective in terms of infection control and the level of hygiene implemented in the herd, test-andcull strategies can be prioritized. Systematic test-and-cull appears cost-effective both in epidemiological and economic terms if implemented from the day one infected cattle is introduced in an initially fully susceptible herd. The tool designed here is flexible and enables studying other control options within a dairy herd.