Table 1.

Major histologic lesions that may impact individual rat health observed at ≥10% prevalence, and demographic characteristics associated with increased odds of having the lesion, among a sample of wild urban Norway rats (Rattus norvegicus) trapped in Vancouver, British Columbia, Canada.

Category	Histologic description	n/N*	Prevalence	95% CI	Demographic characteristics†
Cardiomyopathy	Lymphoplasmacytic myocarditis, fibrosis, and/or myocardial degeneration	128/406	32	27–36	Male sex & heavy body mass
Stomach lesions‡	Hyperkeratosis, mucosal hyperplasia, granulocytic inflammation	231/388	60	54–65	Heavy body mass & sexual maturity
Thyroid follicular hyperplasia	Hypertrophic follicular cells surround small or absent follicular lumens lacking colloid§	142/279	51	45–57	Male sex & heavy body mass
Inducible BALT	Peribronchiolar and/or perivascular lymphoplasmacytic cuffs¦	270/403	67	62–72	Heavy body mass
Tracheitis	Lymphoplasmacytic and/or granulocytic submucosal and/or periglandular inflammation	192/372	52	47–59	Heavy body mass
Interstitial nephritis	Interstitial lymphoplasmacytic inflammation#	121/405	30	26–35	Heavy body mass
Pyelitis	Lymphoplasmacytic inflammation in interstitium immediately adjacent to the renal pelvis	85/255	33	28–40	Heavy body mass, body condition score, & Leptospira interrogans infection

BALT = bronchus-associated lymphoid tissue; CI = confidence interval.

^*The number of rats examined for each lesion varies because not all tissues were available for each individual rat because of sampling error, tissue artifacts, and/or autolysis.

^†Demographic characteristic(s) associated with increased odds of having the lesion as determined by multivariable logistic regression modeling with a random effect for city block to control for clustering.

^‡Lesions were associated with Eucoleus sp. infection including hyperkeratosis (keratin layer >45 μm thick in areas without artificial separation and not adjacent to the limiting ridge [junction with glandular stomach]), mucosal hyperplasia (mucosa is >4–6 cells thick, affecting mainly the basal layers and >25% of the section), and inflammation (keratin pustules and submucosal inflammation with granulocytes infiltrating >2 foci not adjacent to the limiting ridge). Details of statistical associations are available elsewhere.⁸⁵

^§Follicular cells were tall cuboidal-to-columnar and had to affect >50% of the thyroid gland and with ≤10 normal follicles.

^¦Lymphocytes and plasma cells surrounding ≥3 secondary or tertiary bronchioles or 1 primary bronchiole and/or ≥3 blood vessels.

^#Present in ≥2 locations within the renal interstitium and excluding areas immediately adjacent to the renal pelvis.