More importantly, this statement addresses the pre-modern medicine belief that fevers did nt happen because of an infectious pathogen, but because of something that was eaten.

The basis of adaptive immunity lies in the capacity of immune cells to distinguish between the body's own cells and infectious pathogens.

Animals reared in a gnotobiotic colony often have poorly developed immune systems, lower cardiac output, thin intestinal walls and high susceptibility to infectious pathogens.

The studies suggest that the unusual polymorphism of major histocompatibility complex genes has evolved primarily through natural selection by infectious pathogens.

Recent research suggests that infectious pathogens play a much smaller role in the pathogenesis than was commonly assumed only a few years ago.