Nephropathia epidemica and Puumala virus occurrence in relation to bank vole (Clethrionomys glareolus) dynamics and environmental factors in northern Sweden

The objectives of the thesis were to investigate the spatio-temporal patterns of nephropathia epidemica (NE) in humans and Puumala virus (PUU) occurrence in relation to bank vole (Clethrionomys glareolus) dynamics and environmental factors in a region of high incidence of NE in northern Sweden. Nephropathia epidemica is a mild form of hemorrhagic fever with renal syndrome, and in northern Sweden the most prevailing serious febrile viral infection, second to influenza. All serologically confirmed NE cases during 1991-2001 in the four northernmost counties (n = 2,468) were used to establish spatio-temporal patterns of the occurrence of the human disease. Within the study region, the bank voles show marked population fluctuations with 3-4 yr cycles and the incidence of NE has a temporal component strongly correlated to annual numbers of bank voles in autumn. People living in rural dwellings near coastal areas were abundant among notified cases and middle-aged males were over-represented. The patients were often infected in autumn when engaged in activities such as handling of fire wood, gardening or hay-handling near man-made rodent refugia or cleaning/redecorating within one. A proportion of these patients, confident about site of PUU exposure, were used to establish field sites in two separate studies. Firstly a five year study (1995-1999) at six sites spanning a bank vole population cycle, and secondly a spatially extensive study at 32 sites was conducted in autumn 1998. Densities, fluctuations and demography of vole populations differ between sites of known occurrence of NE were compared to random forest sites. Five years of repeated biannual sampling revealed that case sites harbored more bank voles than random forest sites, in particular during population peaks. For the individual bank voles, the probability of PUU infection was significantly higher in population peak year, increased with age and was higher for males than for females. In the spatially extended study, it was found that in particular environmental characteristics associated with old-growth moist forests (i.e. Alectoria spp., Picea abies, fallen wood and Vaccinium myrtillus) were associated with high bank vole numbers and numbers of PUU infected bank voles. This implies that success in circulation and persistence of PUU within local bank vole populations is strongly influenced by the local environments. In future modeling of PUU transmission, influence of bank vole demography and environmental factors should be useful on establishing risk assessments and identifying areas of particular risk of PUU exposure

Predicting High Risk for Human Hantavirus Infections, Sweden

An increased risk for hemorrhagic fever with renal syndrome caused by Puumala hantavirus was forecast for Sweden in 2007. The forecast was based on a predicted increase in the number of Myodes glareolus rodents (reservoir hosts). Despite raised awareness and preparedness, the number of human cases during July 2007–June 2008 was 1,483, a new high

Direct seeding for restoration of mixed oak forests: Influence of distance to forest edge, predator-derived repellent and acorn size on seed removal by granivorous rodents

Restoration of mixed oak forest in northern temperate regions is important for biodiversity and for adaptation of forest management to climate change. Direct seeding has been considered as a cost-effective method for the assisted regeneration of oaks. However, removal of acorns by granivorous rodents hinders its application. Patterns of acorn removal can vary with habitat type, presence of predators, and acorn size. In this field study, we tested the effects of distance to forest edge, predator excrement as a repellent, and acorn size on the performance of direct-seeded oak in southern Sweden. The experiment was carried out at two different sites. Our hypotheses were: (i) in clear-cuts, acorn removal is higher closer to the forest edge compared to open areas, (ii) treatment with predator excrement reduces acorn removal without affecting germination, and (iii) larger acorns will be removed more readily than smaller acorns. Finally, we also investigated if seedlings from larger acorns survive better and grow taller compared to smaller acorns in relation to habitat structure and predator excrement as repellent. Acorn removal differed at the two sites. At Skrylle (older clear-cut), no forest edge effects were found. At Klåveröd (new clear-cut site), our results suggest that removal of acorns was higher in the open clear-cut due to the presence of large slash piles. Less vegetation coverage correlated with lower rates of acorn removal, except near slash piles. Our results therefore suggest that forest managers should reduce understory vegetation and avoid slash piles during direct seeding of oak. Mink excrement failed to protect acorns against removal, but did not reduce acorn germination. Bigger acorns produced taller seedlings but did not enhance overall woodland establishment due to their higher removal rate. Our results further suggest a potential food satiation effect due to an extra supply of additional food. Satiation manipulation might potentially be a method of mitigating the impact of seed predation by granivorous rodents during the direct seeding of oak, but such an approach requires further research before it could be recommended

Seewis hantavirus in common shrew (Sorex araneus) in Sweden

Background Rodent borne hantaviruses are emerging viruses infecting humans through inhalation. They cause hemorrhagic fever with renal syndrome and hemorrhagic cardiopulmonary syndrome. Recently, hantaviruses have been detected in other small mammals such as Soricomorpha (shrews, moles) and Chiroptera (bats), suggested as reservoirs for potential pandemic viruses and to play a role in the evolution of hantaviruses. It is important to study the global virome in different reservoirs, therefore our aim was to investigate whether shrews in Sweden carried any hantaviruses. Moreover, to accurately determine the host species, we developed a molecular method for identification of shrews. Method Shrews (n = 198), caught during 1998 in Sweden, were screened with a pan-hantavirus PCR using primers from a conserved region of the large genome segment. In addition to morphological typing of shrews, we developed a molecular based typing method using sequencing of the mitochondrial cytochrome C oxidase I (COI) and cytochrome B (CytB) genes. PCR amplified hantavirus and shrew fragments were sequenced and phylogenetically analysed. Results Hantavirus RNA was detected in three shrews. Sequencing identified the virus as Seewis hantavirus (SWSV), most closely related to previous isolates from Finland and Russia. All three SWSV sequences were retrieved from common shrews (Sorex araneus) sampled in Vasterbotten County, Sweden. The genetic assay for shrew identification was able to identify native Swedish shrew species, and the genetic typing of the Swedish common shrews revealed that they were most similar to common shrews from Russia. Conclusion We detected SWSV RNA in Swedish common shrew samples and developed a genetic assay for shrew identification based on the COI and CytB genes. This was the first report of presence of hantavirus in Swedish shrews

Puumala Hantavirus Excretion Kinetics in Bank Voles (Myodes glareolus)

One-sentence summary for table of contents: Virus may be transmitted by saliva, urine, and feces, and saliva may play a role in transmission to humans

Human Hantavirus Infections, Sweden

The prevalent human hantavirus disease in Sweden is nephropathia epidemica, which is caused by Puumala virus and shed by infected bank voles (Clethrionomys glareolus). To evaluate temporal and spatial patterns of this disease, we studied 2,468 reported cases from a highly disease-endemic region in northern Sweden. We found that, in particular, middle-aged men living in rural dwellings near coastal areas were overrepresented. The case-patients were most often infected in late autumn, when engaged in activities near or within manmade rodent refuges. Of 862 case-patients confident about the site of virus exposure, 50% were concentrated within 5% of the study area. The incidence of nephropathia epidemica was significantly correlated with bank vole numbers within monitored rodent populations in part of the region. Understanding this relationship may help forestall future human hantavirus outbreaks

Synchrotron XRF Analysis Identifies Cerium Accumulation Colocalized with Pharyngeal Deformities in CeO2 NP-Exposed Caenorhabditis elegans

publishedVersio

Evolutionary Relationships of Ljungan Virus Variants Circulating in Multi-Host Systems across Europe

The picornavirus named ‘Ljungan virus’ (LV, species Parechovirus B) has been detected in a dozen small mammal species from across Europe, but detailed information on its genetic diversity and host specificity is lacking. Here, we analyze the evolutionary relationships of LV variants circulating in free-living mammal populations by comparing the phylogenetics of the VP1 region (encoding the capsid protein and associated with LV serotype) and the 3Dpol region (encoding the RNA polymerase) from 24 LV RNA-positive animals and a fragment of the 5′ untranslated region (UTR) sequence (used for defining strains) in sympatric small mammals. We define three new VP1 genotypes: two in bank voles (Myodes glareolus) (genotype 8 from Finland, Sweden, France, and Italy, and genotype 9 from France and Italy) and one in field voles (Microtus arvalis) (genotype 7 from Finland). There are several other indications that LV variants are host-specific, at least in parts of their range. Our results suggest that LV evolution is rapid, ongoing and affected by genetic drift, purifying selection, spillover and host evolutionary history. Although recent studies suggest that LV does not have zoonotic potential, its widespread geographical and host distribution in natural populations of well-characterized small mammals could make it useful as a model for studying RNA virus evolution and transmission