Knowledge base

To avoid disease transmission it is important to try to keep the sources of infection (e.g. animals, persons, vermin) separated from the susceptible contacts (healthy animals) as much as possible. This can be achieved through the prevention of direct contacts between high-risk (infectious) and low-risk (susceptible) animals, as well as the prevention of indirect contacts.

Even with the best possible biosecurity measures, it is not possible, and probably not even desirable, to keep animals under sterile conditions. Therefore, it is important to have good cleaning and disinfection procedures in place. In that way, biosecurity measures aim at reducing the infection pressure under a level that allows the natural immunity of the animals to cope with the infections.

Some transmission routes may transmit many different pathogens with a high efficiency (e.g. direct animal-animal contact), whereas other transmission routes (e.g. air) are at lower risk of transmitting disease. Therefore, when designing biosecurity control programs, it is of important to focus first on the high-risk transmission routes and only subsequently on the lower risk transmission routes.

Besides the probability of transmission of a pathogen through the different transmission routes, the frequency of occurrence of the transmission route plays a very significant role as well. If a certain transmission route (eg. transmission via hands of animal care takers) has only a low probability of occurrence, but it is repeated very frequently (eg. animal care taker is touching the animals several times a day without precautionary measures), the risk of disease transmission ends up being very substantial anyway.

The larger herds or flocks become, the more important biosecurity measures will be. In large groups of animals, there are more animals that can become infected and maintain an infection cycle to subsequently build up the infection pressure above the limit that the animals can cope with. Moreover, larger herds or flocks have more frequent contacts with the outside world (eg. movements of animals, transport of feed, professional visitors, among others) that all may carry a certain risk of disease introduction. Also in larger and/or high productive herds, the high-producing animals may be more susceptible to disease, and therefore the consequences of disease introduction may be more severe compared to smaller herds.