Gastrointestinal helminths of Norway rat (Rattus norvegicus) from the Belgrade area were studied as a part of a wider ecological research of rats in Serbia (data on the distribution, population ecology, economic and epizoothiological-epidemiological importance, and density control). Rats were captured from May 2005 to July 2009 at both urban and suburban-rural sites. Of a total of 302 trapped rats 48% were males and 52% females, with 36.5% and 38.8% of juvenile-subadult individuals, per sex respectively. Intestinal helminth infection was noted in 68.5% of rats, with a higher prevalence in male hosts and in adult individuals. Higher numbers of infected juveniles-subadults were noted in suburban-rural habitats, while an opposite tendency was noted in adult rats. Seven helminth species were recovered, of which five were nematode (Heterakis spumosa, Nippostrongylus brasiliensis, Capillaria sp., Trichuris muris and Syphacia muris) and two cestode species (Hymenolepis diminuta and Rodentolepis fraterna). The most prevalent parasites were Heterakis spumosa (36.7%) and Hymenolepis diminuta (30.5%). Sex and habitat-related differences were noted in the prevalence of infection with Capillaria sp. and Trichuris muris, while there were no age-related differences in the prevalence of infection with any individual helminth species. Significantly higher prevalence of infection was noted in summer as compared to spring or winter, with a tendency to be higher in autumn as compared to spring. The only significant difference in the prevalence of infection between habitat-related was noted during spring. H. spumosa was most prevalent in summer, while H. diminuta and N. brasiliensis in autumn. The mean intensity of infection with H. spumosa, R. fraterna, S. muris and T. muris was higher in autumn than in the other seasons, while N. brasiliensis and Capillaria sp. occured in winter. No more than four helminth species were found in one host.

The nematode Calodium hepaticum and the cestode Taenia taeniaeformis are zoonotic helminths primarly found in the liver of common wild rats. Most reports on these helminth species with cosmopolitan distribution are from Asia, and there is paucity of data for Europe. Wild Norway rats (Rattus norvegicus) from urban and suburban habitats of the Belgrade area were examined for the presence of Calodium hepaticum and Taenia taeniaeformis larvae liver infections. The presence of visible cysts and a histomorphology of parasite-related inflammatory liver responses were sought as signs of infection. The total prevalence of infection was 10.9% (C. hepaticum) and 29.9% (T. taeniaeformis), with no differences between the sexes. No difference in the annual prevalence of both helminth species was noted. Data obtained in this study provide new information relevant to wild Norway rats as sources of C. hepaticum and T. taeniaeformis liver infection in this geographic area, and, in a wider context, in Europe.

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Basic immune-related health-relevant changes (total and differential white blood cell counts and activity, leukocyte tissue infiltration, and related pathohistology) were assessed in wild Norway rats from urban habitats. Comparative measurements were conducted in individuals of several laboratory strains of Norway rat in order to gain insight into environmental effects on the health of wild rats. Changes in leukocyte counts and activity along with tissue infiltration were noted only in wild rats, indicating systemic as well as tissue inflammation in these animals. Coincidence of these changes with chronic inflammatory pulmonary and kidney disease was observed in the majority of affected rats