DISTRIBUTION AND SEASONAL VARIATION OF LJUNGAN VIRUS IN BANK VOLES (MYODES GLAREOLUS) IN FENNOSCANDIA

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 3D^pol 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.

Geographical Distribution of Ljungan Virus in Small Mammals in Europe

Ljungan virus (LV), which belongs to the Parechovirus genus in the Picornaviridae family, was first isolated from bank voles (Myodes glareolus) in Sweden in 1998 and proposed as a zoonotic agent. To improve knowledge of the host association and geographical distribution of LV, tissues from 1685 animals belonging to multiple rodent and insectivore species from 12 European countries were screened for LV-RNA using reverse transcriptase (RT)-PCR. In addition, we investigated how the prevalence of LV-RNA in bank voles is associated with various intrinsic and extrinsic factors. We show that LV is widespread geographically, having been detected in at least one host species in nine European countries. Twelve out of 21 species screened were LV-RNA PCR positive, including, for the first time, the red vole (Myodes rutilus) and the root or tundra vole (Alexandromys formerly Microtus oeconomus), as well as in insectivores, including the bicolored white-toothed shrew (Crocidura leucodon) and the Valais shrew (Sorex antinorii). Results indicated that bank voles are the main rodent host for this virus (overall RT-PCR prevalence: 15.2%). Linear modeling of intrinsic and extrinsic factors that could impact LV prevalence showed a concave-down relationship between body mass and LV occurrence, so that subadults had the highest LV positivity, but LV in older animals was less prevalent. Also, LV prevalence was higher in autumn and lower in spring, and the amount of precipitation recorded during the 6 months preceding the trapping date was negatively correlated with the presence of the virus. Phylogenetic analysis on the 185 base pair species-specific sequence of the 5' untranslated region identified high genetic diversity (46.5%) between 80 haplotypes, although no geographical or host-specific patterns of diversity were detected.

Seroprevalence of lymphocytic choriomeningitis virus and Ljungan virus in Finnish patients with suspected neurological infections

Directly-transmitted rodent-borne zoonotic viruses, such as lymphocytic choriomeningitis virus (LCMV) can cause nervous system infections. Rodent-borne Ljungan virus (LV) is considered potentially zoonotic possibly causing neurological symptoms. Our objective was to understand the role of these two viruses compared to other pathogens in causing neurological infections in Finnish patients. Routine screening data were available for 400 patients aged 5-50 years, collected from December 2013 to December 2014 with suspected neurological infection. Depending on symptoms, patients were variously tested for herpesviruses, enteroviruses, varicella zoster virus, and Mycoplasma pneumoniae, while those suspected of tick bite were further tested for Borrelia spp. and tick-borne encephalitis virus using antibody and/or nucleic acid tests. For 380 patients, we also screened the RNA and antibody prevalence of LCMV and LV in order to test if either of these viruses were the causative agent. Data collected indicated that the causative microbial agent was confirmed in only 15.5% of all Finnish patients with neurological symptoms, with M. pneumoniae (26 cases) being the most common causative agent found in sera, whereas Borrelia spp. (15), herpes simplex viruses (7), and enteroviruses (5) were the most common agents confirmed in the CSF. The seroprevalences for LV and LCMV were 33.8% and 5.0%, respectively, but no samples were PCR-positive. In this study, M. pneumoniae and Borrelia spp. were the most common causative agents of neurological infections in Finland. No LCMV or LV infections were detected. We conclude there was no association of LV with neurological diseases in this patient cohort.