Only one virus is a candidate and that is Hep A, although it may be a marker for fecal oral contact as much as anything.The best candidates for Old Friends are Necator Americanus and Trichuris trichuria among helminths, and H Pylori among the protozoans, and soil saprophytes like Mycobacterium Vaccae and low virulence salmonella species among the prokaryotes.Pinworm might work immunologically but