Factors associated with the prevalence and pathology of Calodium hepaticum and C. splenaecum in periurban micromammals.

Calodium hepaticum (syn. Capillaria hepatica) and Calodium splenaecum (syn. Capillaria splenaecum) are nematodes that infect the liver and spleen, respectively, of mammals. While the host range, distribution, pathology and zoonotic potential of C. hepaticum are well known, very little is known about C. splenaecum. The observed prevalence of these two parasites, the factors associated with prevalence, and the lesions resulting in the different host species were studied in 408 micromammals captured in two periurban areas of Barcelona (NE Spain) from 2011 to 2013. C. hepaticum was found in 4% of 322 wood mice (Apodemus sylvaticus) (with local prevalence up to 16%) and 1 of 2 Norwegian rats (Rattus norvegicus). C. splenaecum was found in 10 % of 38 greater white-toothed shrew (Crocidura russula) (local prevalence up to 30%). Neither parasite was detected in 29 Algerian mice (Mus spretus) and 17 black rats (Rattus rattus). Prevalence of C. hepaticum was significantly higher in wood mice captured in natural areas (6.4%) than those from residential areas (0%), and infected mice were in better body condition. No differences in prevalence were found among age and sex groups, years and seasons. Lesions of hepatic capillariasis in wood mice consisted mainly of mild to moderate multifocal granulomas around degenerating adult parasites and/or eggs, while lesions seen in a rat consisted of multifocal granulomatous hepatitis and bridging fibrosis extending from the necrotic areas caused by the parasites. Splenic lesions found in shrews due to C. splenaecum, representing the first histological description of this parasite, were single nodules that corresponded to finely encapsulated clusters of eggs with adult parasites.