host-associated 1,904 animal host 1,904 digestive tract 1,904 intestine 1,903 mammalian host 1,724 human host 1,650 industrialized 1,505 adult 771 urban 231 elderly 105 rural 28 adolescent 27 child 21 non-industrialized 17 infant 9 hunter-gatherer 3 full term birth 3 traditional agriculturalist 3 rumen 2