ABSTRACT
Diseases affecting pigs can be quite complex. It is well recognized that often these conditions are multifactorial, especially as in the case of respiratory diseases, hence the term ‘porcine respiratory disease complex’ (PRDC) has been accepted (Brockeier, 2002). The concept of the disease triad (Fig. 1) emphasizes this complexity and the interaction between not only different pathogens, but the host, pathogen and the environment.
