host-associated 526 animal host 526 mammalian host 526 human host 526 digestive tract 522 industrialized 497 mouth 467 adult 341 saliva 324 intestine 261 urban 137 child 127 airways 59 adolescent 40 elderly 13 skin 4 rural 2 non-industrialized 2 infant 1 built environment 1 anthropogenic 1 terrestrial 1