Table 1.

Categories of microscopic changes in the non-glandular stomach of wild urban Norway rats (Rattus norvegicus).

Change	Inclusion criteria	Exclusion criteria
Eucoleus sp. infection	Presence of Eucoleus sp. nematodes or eggs in the mucosa of the ventral tongue, oropharynx, esophagus or non-glandular stomach	Absence of inclusion criteria
Hyperkeratosis	Superficial keratin layer ⩾ 45 μm thick in sections not adjacent to limiting ridge and where keratin is not artifactually separated	Keratin < 45 μm thick or > 45 μm only in areas immediately adjacent to limiting ridge
Keratin pustules	Aggregates of polymorphonuclear cells and cell debris within the superficial keratin	Food debris or superficial bacterial overgrowth
Mucosal hyperplasia	Mucosa ⩾ 5 layers thick affecting ⩾ 25% of the section examined	Mucosa < 5 layers thick or < 25% of the section affected
Submucosal inflammation	Polymorphonuclear cells infiltrating submucosa in ⩾ 2 foci in sections not adjacent to limiting ridge	<2 foci or immediately adjacent to limiting ridge