Introduction

In northern Europe, there is currently a tendency toward more “natural” livestock production. The proponents of this view believe that animals should be kept in herds and able to move about freely, that the (regular) administration of drugs should be reduced, and that it is wrong to destroy whole flocks to eradicate disease. In addition, there remain requirements for economically viable livestock production that yields safe food for human consumption. These aims can be reached in two ways: by complete eradication of certain agents (e.g., by mass vaccination), or by avoidance of disease caused by other agents. In writing about infectious diseases, the terminology often causes confusion. We adhere to the following definitions: agent – the microorganism that can sometimes cause disease (because disease does not always occur, and because the effect may even be favorable, the term pathogen is avoided); infection – colonization of the host (i.e., some replication of the agent in the host); and disease – clinical symptoms of the host caused by the agent. Eradication is preferable when the disease causes severe economic damage (e.g., foot-and-mouth disease, classic swine fever) or when there are serious consequences for human health (e.g., bovine tuberculosis, bovine spongiform encephalopathy).

When there is a high rate of reintroduction (e.g., from other animal species), the monetary costs to restore the infection-free status again and again can be higher than the losses caused by the disease.