Factors Inherent in the Pathogen Affecting Establishment and Course of Disease

Variation in the infection capacity of a pathogen may be due to different relationships: the actual stage in the life-cycle of the pathogen, the variability in terms of biotype or race and the virulence of the pathogen in terms of the amount of inoculum needed to establish infection. These factors will be discussed in the following sections: (1) pathogenicity as related to the life-cycle or ontogenesis of the pathogen, (2) pathogenicity as related to physiologic or pathogenic races or strains of the pathogen (pathotypes), (3) pathogenicity as related to infection potential of the pathogen, (4) pathogenicity as related to the actual condition of the pathogen. These aspects are all important with regard to seed transmission of the pathogen and to their bearing on further secondary spread of disease.