Evidence for Ljungan virus specific antibodies in humans and rodents, Finland.

Objectives Ljungan virus (LV) belongs to the genus Parechovirus. Human parechoviruses (HPeV) are common viruses causing diarrhea and gastroenteritis, and the first infection is commonly faced during the early childhood and 90% of humans acquire HPeV antibodies by the age of two. Ljungan virus, however, is known as a rodent-borne parechovirus first isolated (LV 87-012) near Ljungan river in Sweden from a wild bank vole (Myodes glareolus). Puumala hantavirus causes Nephropatia epidemica (NE) in humans and these cases are fairly common in Finland comprising approximately 800-3000 suspected NE cases per year depending somewhat on the size of rodent population. However, the abundance of Finnish patients diagnosed with NE, i.e., with a history of rodent contact, makes any connection between human disease and Ljungan virus infection likely to be found in the country. With this study, we sought to find evidence of Ljungan virus in Finnish humans and rodents. We aimed to develop a reliable method for serological screening of LV in humans and rodents, and to confirm the specificity of this method. Methods Initially, neutralization assays were designed and carried out followed by an immunofluorescent assay (IFA) for serology screening. The IFA and neutralization assays were set up using Vero-cells infected with Ljungan virus strain 145SLG kindly provided by Conny Tolf et al. (Uppsala University, Uppsala, Sweden). Serological assays were used for detecting Ljungan virus antibodies both in humans and rodents. Furthermore, 8 human sera used in the Ljungan virus neutralization assay were cross-checked for titres of neutralizing antibodies to six different human parechoviruses (HPeV 1-6), that are closely related to Ljungan virus. Neutralization effect of the antibodies to 42 different human picornaviruses against Ljungan virus (145SLG) was also studied. Results and Conclusion The study is ongoing, but preliminary data indicates that we have LV specific antibodies in Finland. Twenty-six sera out of 41 human serums were not able to neutralize Ljungan 145SLG virus. However, 15 human serum samples neutralized the Ljungan 145SLG virus. Wide titer range of the HPeV 1-6 antibodies were also detected in eight human serums studied in more closely. The preliminary IFA results are also supporting the neutralization results. In total, 8 out of the 50 (16%, 95% CI: 8.1–28.8%) rodent samples (Konnevesi, Finland, year 2008) were Ljungan antibody positive. Our data is first evidence of human Ljungan virus infections in Finland both in humans and rodents. This data can be used as a stepping stone for further studies of Ljungan virus: the broad seroprevalence study both in humans and rodents, and to investigate the role of Ljungan virus infection in Finland.