Despite complete movement bans and other bio-security measures, transmission of infectious animal diseases occurred during the last epidemics of, for example, foot-and-mouth disease, classical swine fever and avian influenza in the Netherlands and abroad.
With the aid mathematical modelling it has been shown that the transmission between spatially separated animals as observed in transmission experiments does not take place via direct (airborne) transmission, but rather through slow contamination of the environment between sending and receiving animals (via a combination of transport processes). This process is characterised by a build-up of infectious material in the environment until enough infectious material is accumulated at the receiving animal to cause infection.
Decay rate of the pathogen
The duration of this delay before first transmission occurs proved to be highly dependent on the decay rate of the pathogen in the environment. This form of transmission was shown to play an important role in intensive care units of hospitals too. Another important conclusion from the research is that transmission of pathogens with a low decay rate can occur at distant locations and long after an infectious source is removed.