Biomedical subjects
Publications and source records attributed to R Wiger.
2 freely growing confined populations of Norwegian lemmings displayed population peaks and declines which were similar to natural populations. In most other studies of confined populations of rodents, the number of animals stabilized and maintained fairly constant numbers. Juvenile mortality and reduced pregnancy rate contributed to the decline.
Ultrastructure of the cuticle and pseudobursa of adult males of four species of Trichinella has been studied by SEM. T. nativa differs markedly from T. spiralis, T. nelsoni and Trichinella sp. in the form of the pseudobursa. Trichinella sp. differs only slightly from T. spiralis and T. nelsoni. The ultrastructure of the cuticle revealed no characters suitable for the differentiation of the taxons under study.
Five virus strains with close serological relationship to the tick-borne encephalitis (TBE) complex have been isolated from Ixodes ricinus ticks. The ticks were collected in early June 1976 at three different locations in Sogn & Fjordane County, Norway. One of the virus-yielding pools was composed of ticks collected between the cabins on a tourist camping ground.
Three virus strains serologically related to the California encephalitis group (Bunyaviridae) of arboviruses were isolated from 7331 mosquitoes collected in Norway in June-August 1975. Two of the isolates (S 548 and S 618) seemed to be closely related and the third, S 568, more distantly related by serological techniques to Tahyna virus. Viruses were found in the mosquito species Aedes sticticus, A. diantaeus and A. hexodontus colllected (in order) from Oyern (59 degrees N, 11 degrees 12' E), Trandum (60 degrees 08' N, 11 degrees 10' E) and Masi (69 degrees 26' N, 23 degrees 39' E). The Masi isolate seems to be the northernmost arbovirus isolate in the world so far. Strain S 568 was from 16 male A. diantaeus, indicating transovarial transmission of the virus. An accidental infection demonstrated the potential human pathogenicity of one of the newly-isolated strains (S 568), and the ability of CE viruses to persistently infect suckling mouse brains was indicated by in vivo findings. The biological characteristics of the new strains so far investigated are consistent with those of the California encephalitis group. During this work the Aerosil absorption method for production of haemagglutinating antigens proved useful for Tahyna virus and the newly-isolated strains. Trypsinization of erythrocytes improved the haemagglutinating capacities of these viruses.
Experimental infections of Babesia microti in laboratory-reared Clethrionomys glareolus revealed that approximately 15% of the erythrocytes were infected with single ring forms during peak parasitemia. Infected erythrocytes could be detected in blood smears up to one month post infection. C. glareolus treated with a single injection of Depo-Medrol i.m. two days prior to infection displayed a four-fold increase in number of infected erythrocytes at peak parasitemia, 35% of which contained more than one Babesia, and a prolongation of the infection. B. microti infections in 35 laboratory--reared Lemmus lemmus were fatal. Multiple invasion of erythrocytes, anemia, icterus, hemoglobinuria, anorexia and weight loss, and adrenal and splenic hypertrophy were characteristic for B. microti infections in Norwegian lemmings.
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Both natural and experimental Trypanosoma lemmi infections in Norwegian lemmings caused slight anemias and hypoglycemia. Leucocyte counts remained the same. Adrenal and splenic hypertrophy were associated with natural infections whereas only splenic hypertrophy was present in the experimental infection. Grahamella sp. infections were also associated with adrenal and splenic hypertrophy in wild lemmings. It is suggested that blood parasites which are associated with anemia, hypoglycemia and adrenal hypertrophy might also interfere with both male and female reproduction, and should be considered in the interpretation of the population regulation of small rodents.