Lesions associated with Eucoleus sp. in the non-glandular stomach of wild urban rats (Rattus norvegicus)

• We used histology to examine wild rats for stomach pathology.
• Reactive lesions in the stomach of wild rats were associated with Eucoleus sp.
• Sexually mature and heavy rats had increased odds of infection.
• This represents a substantial host response to parasitism.

Histological lesions associated with Eucoleus sp. infection of the non-glandular stomach were discovered in a wild, urban population of Norway rats (Rattus norvegicus) trapped over a 1-year period in Vancouver, Canada. Four distinct categories of histological lesions in the non-glandular stomach were identified in association with infection in a sample of 183 rats. The apparent prevalence of Eucoleus sp. in the upper gastrointestinal tract (ventral tongue, oropharynx, esophagus and non-glandular stomach) was 43.1% (79/183). Infection with Eucoleus sp. was significantly associated with hyperkeratosis, mucosal hyperplasia, keratin pustules and submucosal inflammation in the non-glandular stomach (P < 0.05). Eucoleus sp. infection and/or related stomach pathology was present in 135/183 (73.8%) of rats. Statistical analysis showed the odds of being affected by Eucoleus sp. or associated stomach pathology were greater in heavier (OR = 1.06, 95% CI = 1.00–1.12) and sexually mature rats (OR = 4.64, 95% CI = 1.23–17.10). Eucoleus sp. infection is common in wild rats in Vancouver and induces substantial host response. The impact of Eucoleus sp. and associated lesions on the health of individual rats and the population as a whole remains to be investigated.

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