Dynamic effects of predators on cyclic voles: field experimentation and model extrapolation. (49/710)

Mechanisms generating the well-known 3-5 year cyclic fluctuations in densities of northern small rodents (voles and lemmings) have remained an ecological puzzle for decades. The hypothesis that these fluctuations are caused by delayed density-dependent impacts of predators was tested by replicated field experimentation in western Finland. We reduced densities of all main mammalian and avian predators through a 3 year vole cycle and compared vole abundances between four reduction and four control areas (each 2.5-3 km(2)). The reduction of predator densities increased the autumn density of voles fourfold in the low phase, accelerated the increase twofold, increased the autumn density of voles twofold in the peak phase, and retarded the initiation of decline of the vole cycle. Extrapolating these experimental results to their expected long-term dynamic effects through a demographic model produces changes from regular multiannual cycles to annual fluctuations with declining densities of specialist predators. This supports the findings of the field experiment and is in agreement with the predation hypothesis. We conclude that predators may indeed generate the cyclic population fluctuations of voles observed in northern Europe.  (+info)

Cross-protection against challenge with Puumala virus after immunization with nucleocapsid proteins from different hantaviruses. (50/710)

Hantaviruses are rodent-borne agents that cause hemorrhagic fever with renal syndrome or hantavirus pulmonary syndrome in humans. The nucleocapsid protein (N) is relatively conserved among hantaviruses and highly immunogenic in both laboratory animals and humans, and it has been shown to induce efficient protective immunity in animal models. To investigate the ability of recombinant N (rN) from different hantaviruses to elicit cross-protection, we immunized bank voles with rN from Puumala (PUUV), Topografov (TOPV), Andes (ANDV), and Dobrava (DOBV) viruses and subsequently challenged them with PUUV. All animals immunized with PUUV and TOPV rN were completely protected. In the group immunized with DOBV rN, 7 of 10 animals were protected, while only 3 of 8 animals were protected in the group immunized with ANDV rN, which is more closely related to PUUV rN than DOBV rN. Humoral and cellular immune responses after rN immunization were also investigated. The highest cross-reactive humoral responses against PUUV antigen were detected in sera from ANDV rN-immunized animals, followed by those from TOPV rN-immunized animals, and only very low antibody cross-reactivity was observed in sera from DOBV rN-immunized animals. In proliferation assays, T lymphocytes from animals immunized with all heterologous rNs were as efficiently recalled in vitro by PUUV rN as were T lymphocytes from animals immunized with homologous protein. In summary, this study has shown that hantavirus N can elicit cross-protective immune responses against PUUV, and the results suggest a more important role for the cellular arm of the immune response than for the humoral arm in cross-protection elicited by rN.  (+info)

Molecular cloning of a vaccine antigen against infection with the larval stage of Echinococcus multilocularis. (51/710)

Alveolar and cystic hydatidosis are caused by infection with the larval stages of Echinococcus multilocularis and Echinococcus granulosus, respectively. A host-protective antigen has been identified in E. granulosus. Here we identify the presence of a closely related protein in E. multilocularis, characterize and express a cDNA encoding the antigen (designated EM95), determine the structure of the em95 gene, and demonstrate that the EM95 recombinant protein can be used to induce significant levels of protection against challenge infection with E. multilocularis eggs in mice.  (+info)

Demographic factors associated with hantavirus infection in bank voles (Clethrionomys glareolus). (52/710)

The bank vole (Clethrionomys glareolus) is the natural reservoir of Puumala virus (PUUV), a species in the genus Hantavirus. PUUV is the etiologic agent of nephropathia epidemica, a mild form of hemorrhagic fever with renal syndrome. Factors that influence hantavirus transmission within host populations are not well understood. We evaluated a number of factors influencing on the association of increased PUUV infection in bank voles captured in a region in northern Sweden endemic for the virus. Logistic regression showed four factors that together correctly predicted 80% of the model outcome: age, body mass index, population phase during sampling (increase, peak, or decline/low), and gender. This analysis highlights the importance of population demography in the successful circulation of hantavirus. The chance of infection was greatest during the peak of the population cycle, implying that the likelihood of exposure to hantavirus increases with increasing population density.  (+info)

Behavioral, physiologic, and habitat influences on the dynamics of Puumala virus infection in bank voles (Clethrionomys glareolus). (53/710)

Populations of bank voles (Clethrionomys glareolus) were monitored during a 4-year study in southern Belgium to assess the influence of agonistic behavior, reproductive status, mobility, and distribution of the rodents on the dynamics of Puumala virus (abbreviation: PUUV; genus: Hantavirus) infection. Concordance was high between data from serologic testing and results of viral RNA detection. Wounds resulting from biting or scratching were observed mainly in adult rodents. Hantavirus infection in adults was associated with wounds in the fall, i.e., at the end of the breeding season, but not in spring. In addition, sexually active animals were significantly more often wounded and positive for infection. Hantavirus infection was associated with higher mobility in juvenile and subadult males. Seroconversions observed 6 months apart also occurred more frequently in animals that had moved longer distances from their original capture point. During nonepidemic years, the distribution of infection was patchy, and positive foci were mainly located in dense ground vegetation.  (+info)

A blond coat color variation in meadow vole (Microtus pennsylvanicus). (54/710)

Color mutations occur frequently among rodents. Here we describe a blond coat color mutation in the meadow vole (Microtus pennsylvanicus) that arose in a captive breeding colony established from wild-caught animals from southern Illinois. The blond coat coloration results from changes in the color and distribution of pigments in the hair. The mutation is monogenic autosomal recessive.  (+info)

Mycobacterium microti infection (vole tuberculosis) in wild rodent populations. (55/710)

Mycobacterium microti (vole tuberculosis) infections in small wild mammals were first described more than 60 years ago in several populations in Great Britain. Few studies of vole tuberculosis have been undertaken since then, and little is known about the relationship between M. microti isolates originating from different populations or at different times or of the prevalence of this infection in wild rodent populations, despite human cases of M. microti infections being increasingly reported. In this study, field voles (Microtus agrestis), bank voles (Clethrionomys glareolus), and wood mice (Apodemus sylvaticus) were found to be infected, with up to 8% having external tuberculous signs, in wild populations in Northumberland and Cheshire, England. Spoligotyping applied directly to the clinical material simultaneously detected and typed M. microti bacteria in skin lesions, lymph glands, and internal abcesses. IS6110 restriction fragment length polymorphism typing of cultured bacteria was used to compare these isolates with previously isolated strains from both animals and humans. This demonstrated that although the current rodent isolates were distinct from those isolated from voles in the 1930s in Great Britain, they had a high degree of similarity to these strains and were distinct from the M. microti isolates from humans, a pig, and a ferret from The Netherlands. Thus, M. microti infection seems to be widespread in wild rodent populations, but more studies are needed to understand how M. microti might be transmitted from animals to humans and to determine better the zoonotic risk posed.  (+info)

Relationship of sertoli-sertoli tight junctions to ectoplasmic specialization in conventional and en face views. (56/710)

Ectoplasmic specializations are actin filament-endoplasmic reticulum complexes that occur in Sertoli cells at sites of intercellular attachment. At sites between inter-Sertoli cell attachments, near the base of the cells, the sites are also related to tight junctions. We studied the characteristics of ectoplasmic specializations from six species using conventional views in which thin sections were perpendicular to the plane of the membranes, we used rare views in which the sections were in the plane of the membrane (en face views), and we also used the freeze-fracture technique. Tissues postfixed by osmium ferrocyanide showed junctional strands (fusion points between membranes) and actin bundles, actin sheets, or both, which could be visualized simultaneously. En face views demonstrated that the majority of tight junctional strands ran parallel to actin filament bundles. Usually, two tight junctional strands were associated with each actin filament bundle. Parallel tight junctions were occasionally extremely close together ( approximately 12 nm apart). Tight junctional strands were sometimes present without an apparent association with organized actin bundles or they were tangential to actin bundles. En face views showed that gap junctions were commonly observed intercalated with tight junction strands. The results taken together suggest a relationship of organized actin with tight junction complexes. However, the occasional examples of tight junction complexes being not perfectly aligned with actin filament bundles suggest that a precise and rigidly organized actin-tight junction relationship described above is not absolutely mandatory for the presence or maintenance of tight junctions. Species variations in tight junction organization are also presented.  (+info)