Could myocarditis, insulin-dependent diabetes mellitus, and Guillain-Barré syndrome be caused by one or more infectious agents carried by rodents?

The numbers of small rodents in northern Sweden fluctuate heavily, peaking every 3 or 4 years. We found that the incidence of Guillain-Barré syndrome and insulin-dependent diabetes mellitus, as well as the number of deaths caused by myocarditis, followed the fluctuations in numbers of bank voles, although with different time lags. An environmental factor, such as an infectious agent, has been suggested for all three diseases. We hypothesize that Guillain-Barré syndrome, myocarditis, and insulin-dependent diabetes mellitus in humans in Sweden are caused by one or more infectious agents carried by small rodents. Also, a group of novel picornaviruses recently isolated from these small rodents is being investigated as the possible etiologic agent(s)

Surveillance of Echinococcus multilocularis in rodents in the vicinity of the finding of the first infected red fox (Vulpes vulpes) in Sweden

Olsson, G.E., Hörnfeldt, B., Ågren, E., Wahlström, H

How predation and landscape fragmentation affect vole population dynamics

Background: Microtine species in Fennoscandia display a distinct north-south gradient from regular cycles to stable populations. The gradient has often been attributed to changes in the interactions between microtines and their predators. Although the spatial structure of the environment is known to influence predator-prey dynamics of a wide range of species, it has scarcely been considered in relation to the Fennoscandian gradient. Furthermore, the length of microtine breeding season also displays a north-south gradient. However, little consideration has been given to its role in shaping or generating population cycles. Because these factors covary along the gradient it is difficult to distinguish their effects experimentally in the field. The distinction is here attempted using realistic agent-based modelling. Methodology/Principal Findings: By using a spatially explicit computer simulation model based on behavioural and ecological data from the field vole (Microtus agrestis), we generated a number of repeated time series of vole densities whose mean population size and amplitude were measured. Subsequently, these time series were subjected to statistical autoregressive modelling, to investigate the effects on vole population dynamics of making predators more specialised, of altering the breeding season, and increasing the level of habitat fragmentation. We found that fragmentation as well as the presence of specialist predators are necessary for the occurrence of population cycles. Habitat fragmentation and predator assembly jointly determined cycle length and amplitude. Length of vole breeding season had little impact on the oscillations. Significance: There is good agreement between our results and the experimental work from Fennoscandia, but our results allow distinction of causation that is hard to unravel in field experiments. We hope our results will help understand the reasons for cycle gradients observed in other areas. Our results clearly demonstrate the importance of landscape fragmentation for population cycling and we recommend that the degree of fragmentation be more fully considered in future analyses of vole dynamics

Milder winters in northern Scandinavia may contribute to larger outbreaks of haemorrhagic fever virus

The spread of zoonotic infectious diseases may increase due to climate factors such as temperature, humidity and precipitation. This is also true for hantaviruses, which are globally spread haemorrhagic fever viruses carried by rodents. Hantaviruses are frequently transmitted to humans all over the world and regarded as emerging viral diseases. Climate variations affect the rodent reservoir populations and rodent population peaks coincide with increased number of human cases of hantavirus infections. In northern Sweden, a form of haemorrhagic fever called nephropathia epidemica (NE), caused by the Puumala hantavirus (PUUV) is endemic and during 2006–2007 an unexpected, sudden and large outbreak of NE occurred in this region. The incidence was 313 cases/100,000 inhabitants in the most endemic areas, and from January through March 2007 the outbreak had a dramatic and sudden start with 474 cases in the endemic region alone. The PUUV rodent reservoir is bank voles and immediately before and during the peak of disease outbreak the affected regions experienced extreme climate conditions with a record-breaking warm winter, registering temperatures 6–9°C above normal. No protective snow cover was present before the outbreak and more bank voles than normal came in contact with humans inside or in close to human dwellings. These extreme climate conditions most probably affected the rodent reservoir and are important factors for the severity of the outbreak

Female offspring desertion and male-only care increase with natural and experimental increase in food abundance

In species with biparental care, one parent may escape the costs of parental care by deserting and leaving the partner to care for the offspring alone. A number of theoretical papers have suggested a link between uniparental offspring desertion and ecological factors, but empirical evidence is scarce. We investigated the relationship between uniparental desertion and food abundance in a natural population of Tengmalm's owl Aegolius funereus, both by means of a 5-year observational study and a 1-year experimental study. Parents and offspring were fitted with radio-transmitters in order to reveal the parental care strategy (i.e. care or desert) of individual parents, and to keep track of the broods post-fledging. We found that 70 per cent of the females from non-experimental nests deserted, while their partner continued to care for their joint offspring alone. Desertion rate was positively related to natural prey population densities and body reserves of the male partner. In response to food supplementation, a larger proportion of the females deserted, and females deserted the offspring at an earlier age. Offspring survival during the post-fledging period tended to be lower in deserted than in non-deserted broods. We argue that the most important benefit of deserting may be remating (sequential polyandry)

Distribution of Ljungan virus in Fennoscandia

In 1998 a new virus, named ‘Ljungan’ (LV) was isolated in wild populations of bank voles (Myodes glareolus) in Sweden (Niklasson et al, 1998), and soon after in Denmark and the USA. LV is one of two species of the Parechovirus genus within the Picornaviridae family. Interestingly, there is some evidence that LV may cause diabetes-like symptoms in the bank vole and laboratory mouse (Mus musculus). In addition, it has also been suggested that this virus may be associated with human pathologies such as intrauterine fetal deaths (IUFD), CNS malformations (hydrocephaly and anencephaly), and Sudden Infant Death Syndrome (SIDS). Some authors maintain that LV should be considered a potential zoonotic agent (e.g. Greene Macdonald, 2009), while others are distinctly more sceptical (e.g. Hindersson et al., 2005; Krous et Langlois, 2009; Tapia et al., 2010). Recent optimization and testing of a serological test show that humans can be infected with LV (Jääskeläinen et al 2013). One hypothesis is that the bank vole and other rodents could act as reservoirs and/or vectors of LV. Therefore, knowledge of LV’s geographical and host range is crucial to assessing its potential importance as human pathogen and identifying zoonotic reservoirs. Tissue samples are currently being collected from rodents across the EU as part of the EU FP7 project EDENext and ongoing molecular studies suggest that LV has a wide geographical and host distribution, including commensal species. Here we present recent results of the distribution of the virus in 457 samples (17 sites) across Sweden and Finland, one of the most intensive prevalence studies conducted thus far. These results suggest that LV has a focal distribution along the coast. Future studies will include comparative phylogenomics and identification of possible strains of LV, as well as temporal variation in infection, mode of transmission, and ecological (biotic and abiotic) correlation