[Infectious disease factors in poultry].

The increased importance of multicausal diseases of poultry in the present time is due to a better control and prevention of the monocausal diseases and epidemics predominant in the past. This development is supported by the intensive methods of modern poultry husbandry, the high stocking densities and the improved performance of the poultry by genetic selection. Opportunistic as well as pathogenic organisms can be involved in the development of infectious factorial diseases. A variety of clinical signs can be observed. Above all immunosuppression accompanied by mixed infections and other factors causes health problems of great economical importance. Frequently series of events take place in the development of infectious factorial diseases, in the course of which a preceding disturbance acts as factor of further diseases. Some examples of diseases and syndroms are given to substantiate the multiple involvement of different factors and infections in the development of series of events.