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As part of studies on the nature of the endemic virus infections in natural rodent hosts, the possible association of cyst forms of Pneumocystis spp. with the presence of hanta-, cowpox-, and arenavirus antibodies in wild mice (Apodemus flavicollis, N=105; Apodemus agrarius, N=63; Micromys minutus, N=50) and the common shrew (Sorex araneus, N=101) was studied in south-central Finland. One hantavirus (Saaremaa virus, SAAV) seropositive A. agrarius, and 2 cowpoxvirus (CPXV) seropositive S. araneus were detected, and antibodies against an arenavirus (Lymphocytic choriomeningitis virus, LCMV) were found in all 3 mouse species but not in shrews. Cyst forms of Pneumocystis spp. were detected in all species except A. agrarius. There was no significant association between virus antibodies (LCMV in mice, and CPXV in shrews) and cyst forms of Pneumocystis in any of the species. Concurrent presence of virus antibodies (LCMV) and cyst forms of Pneumocystis were detected only in 1 M. minutus. In conclusion, we found no evidence of any association between Pneumocystis and antibodies to any of the viruses tested.

The microparasite component communities of 2 species of shrews, Notiosorex crawfordi and Sorex ornatus, were investigated for the first time in 2 isolated and 3 continuous landscapes in southern California. With microscopical examination, a total of 6 parasite species was found in N. crawfordi and 8 species in S. ornatus. The highest number (5) of parasite species was detected in the lungs. The corrected estimate of parasite species richness did not significantly correlate with the host abundance in either shrew species. Altitude, and also latitude in N. crawfordi, appeared to be significantly positively associated with the parasite species richness, but this could be due to a false association because of the rare occurrence of some of the parasites or the small altitude range (or both). No other landscape variable analyzed (location, size of the study site, disturbance) was significantly associated with the parasite species richness of the shrews. The parasite assemblages of the 2 shrew species were similar despite the fact that N. crawfordi has a lower metabolic rate than S. ornatus.

Cyst forms of the opportunistic fungal parasite Pneumocystis carinii were found in the lungs of 34% of the desert shrew, Notiosorex crawfordi (n = 59), 13% of the ornate shrew, Sorex ornatus (n = 55), 6% of the dusky-footed wood rat, Neotoma fuscipes (n = 16), 2.5% of the California meadow vole, Microtus californicus (n = 40), and 50% of the California pocket mouse, Chaetodipus californicus (n = 2) caught from southern California between February 1998 and February 2000. Cysts were not found in any of the harvest mouse, Reithrodontomys megalotis (n = 21), California mouse, Peromyscus californicus (n = 20), brush mouse, Peromyscus boylii (n = 7) or deer mouse, Peromyscus maniculatus (n = 4) examined. All infections were mild; extrapulmonary infections were not observed. Other lung parasites detected were Hepatozoon sp./spp. from M. californicus and Notiosorex crawfordi, Chrysosporium sp. (Emmonsia) from M. californicus, and a nematode from S. ornatus.

Seasonal dynamics of Pneumocystis carinii in the field vole, Microtus agrestis, and in the common shrew, Sorex araneus, were investigated in southern and central Finland by microscopical examination of methenamine silver-stained tissue sections. In both host species at both localities the number of P. carinii cyst forms was highest in late autumn (November). In S. araneus, prevalence was higher than in M. agrestis during all seasons. None of the animals was heavily infected or apparently ill, and neither species showed any extrapulmonary dissemination. In this study covering an increase phase and 4 peak host-density phases of the vole cycle, the occurrence of P. carinii seemed to be related to the population density of M. agrestis.

We examined 30 Sorex cinereus, 5 Sorex fumeus, and 21 Blarina brevicauda collected from Pennsylvania in 1995 for blood parasites. Trypomastigotes of Trypanosoma sp. were visible in 13% of the S. cinereus. Ten percent of S. cinereus, 20% of S. fumeus, and 14% of B. brevicauda were infected with Bartonella sp. (or spp.). In S. cinereus, we detected no concurrent Trypanosoma and Bartonella infections.

We examined lung parasites of three species of soricids, Sorex cinereus (n = 58), Sorex fumeus (n = 23) and Blarina brevicauda (n = 45) collected from Pennsylvania (USA), from 1990 to 1995. Yeast-like cells of Hisfoplasma capsulatum var. capsulatum were found in lung sections stained with Grocott's modification of Gomori's methenamine silver, periodic acid-Schiff, Giemsa, and hematoxylin-eosin in two (3%) S. cinereus, eight (35%) S. fumeus and two (4%) B. brevicauda. The number of spores of H. capsulatum in the lungs was low and no inflammatory reaction was evident. The infection was not disseminated to other organs. This is the first report of H. capsulatum infection in any species of shrews of the genus Sorex and the prevalence in S. fumeus was remarkably high compared to those reported for other wild mammals. A nematode, possibly Angiostrongylus michiganensis, was found in the lungs of one S. fumeus on necropsy and in a stained lung section of one S. cinereus. In both cases the host was also infected with the fungus. Pneumocystis carinii, which is the most common lung parasite in Sorex araneus (the numerically dominant Eurasian species of shrew), was not found in any of the North American species of shrew examined in this study.

We carried out an immunohistological and morphological study on Pneumocystis carinii originating from the common shrew, Sorex araneus. Immunologic properties were studied by applying two commercially available immunofluorescence staining kits with differing developmental form specificity to a lung homogenate. The cyst form-specific staining kit reacted with cysts originating from S. araneus. Ultrastructurally this particular antigen epitope specifically deposited on the electron-lucent middle layer of the cyst pellicle. The immunohistochemical staining kit reacting with both cyst and trophozoite forms from human and rat origin did not react with any developmental forms of P. carinii originating from S. araneus. Both kits demonstrated P. carinii in the lung homogenate of a field vole, Microtus agrestis. In morphologic examination, the methenamine silver-stained cyst forms of P. carinii from S. araneus and from M. agrestis differed in size from each other and from those originating from laboratory rats. Ultrastructurally P. carinii from S. araneus did not differ from organisms of rat origin.

Histologic and quantitative techniques were compared in an evaluation of the intensity of Pneumocystis carinii infection in common shrews (Sorex araneus) at Espoo, southern Finland, from September 1992 to May 1993. The histological scores were comparable to the results of the cyst count technique. The number of P. carinii cysts found in common shrews was low compared to those reported by others in clinically ill laboratory rats. The inflammatory changes detected in the lung sections had no significant relation to the presence of P. carinii infection.

The prevalence of Pneumocystis carinii was compared in two species of shrews, Sorex araneus and Sorex caecutiens in Finnish Lapland. The overall prevalence of P. carinii in S. araneus was 70% and in S. caecutiens was 17%. The prevalence for S. araneus is the highest reported for wild animals. The interspecific differences in prevalence were significant for all sex and age groups except for adult males. Based on multiway contingency tables (log-linear models), there was no dependence between sex or age of S. araneus and occurrence of P. carinii. In individual S. araneus the intensity of P. carinii was not related to the total number of helminths or the number of helminth species, and no dependence was observed between the presence of P. carinii and various helminth species.