Surveillance of endemic foci of tick-borne encephalitis in Finland 1995-2013: evidence of emergence of new foci.

The geographical risk areas for tick-borne encephalitis (TBE) in Finland remained the same until the beginning of the 21st century, but a considerable geographical expansion has been observed in the past 10 years. In order to support public health measures, the present study describes the number of laboratory-confirmed TBE cases and laboratory tests conducted and the associated trends by hospital district, with a particular emphasis on the suspected geographical risk areas. An additional investigation was conducted on 1,957 clinical serum samples throughout the country taken from patients with neurological symptoms to screen for undiagnosed TBE cases. This study identified new TBE foci in Finland, reflecting the spread of the disease into new areas. Even in the most endemic municipalities, transmission of TBE to humans occurred in very specific and often small foci. The number of antibody tests for TBE virus more than doubled (an increase by 105%) between 2007 and 2013. Analysis of the number of tests also revealed areas in which the awareness of clinicians may be suboptimal at present. However, it appears that underdiagnosis of neuroinvasive TBE is not common.

Characterization of a novel flavivirus from mosquitoes in northern europe that is related to mosquito-borne flaviviruses of the tropics.

A novel flavivirus was isolated from mosquitoes in Finland, representing the first mosquito-borne flavivirus from Northern Europe. The isolate, designated Lammi virus (LAMV), was antigenically cross-reactive with other flaviviruses and exhibited typical flavivirus morphology as determined by electron microscopy. The genomic sequence of LAMV was highly divergent from the recognized flaviviruses, and yet the polyprotein properties resembled those of mosquito-borne flaviviruses. Phylogenetic analysis of the complete coding sequence showed that LAMV represented a distinct lineage related to the Aedes sp.-transmitted human pathogenic flaviviruses, similarly to the newly described Nounané virus (NOUV), a flavivirus from Africa (S. Junglen et al., J. Virol. 83:4462-4468, 2009). Despite the low sequence homology, LAMV and NOUV were phylogenetically grouped closely, likely representing separate species of a novel group of flaviviruses. Despite the biological properties preferring replication in mosquito cells, the genetic relatedness of LAMV to viruses associated with vertebrate hosts warrants a search for disease associations.

Diagnostics of Pogosta disease: antigenic properties and evaluation of Sindbis virus IgM and IgG enzyme immunoassays.

Sindbis virus (SINV) is a mosquito-borne causative agent of a fever-rash arthritis, Pogosta disease, as verified recently by virus isolation from acutely ill patients. Pogosta disease occurs annually, but it emerges as unique epidemics every 7 years in Finland; over 10,000 patient samples have been analyzed for SINV antibodies, with over 2000 diagnosed acute SINV infections. However, the performance of these serological tests with a large number of samples has not been described before. The aim of the present study was to characterize and evaluate methods developed for the serodiagnostics of SINV infection, suitable for large sample numbers, and to examine the protein-specific responses to the antigen used. We developed SINV IgM and IgG enzyme immunoassays (EIA) using highly purified SINV. The EIAs were compared to hemagglutination inhibition (HI) and neutralization tests. We studied paired samples from 46 acutely ill patients taken at approximately 2-week intervals, with a verified SINV infection confirmed by a fourfold rise in HI antibody titer. The assay cut-off values and specificity were determined with confirmed negative sera. Protein-specific antibody responses were examined with immunoblot assay. The optical density values of the EIAs correlated well with the HI titers. The sensitivities of the IgM and IgG EIAs were 97.6% and 100%, and specificities were 95.2% and 97.6%, respectively. We consider that a verified serological diagnosis of acute SINV infection requires (1) in addition to a positive IgM result at least a fourfold increase in HI (or IgG) titer between paired sera or (2) a positive IgM result and a negative/borderline IgG result (which excludes old immunity) and specific reaction in HI. Both E1 and E2 glycoproteins of SINV were shown to be recognized by IgM and IgG antibodies early in infection.

Sindbis virus infection in resident birds, migratory birds, and humans, Finland.

Sindbis virus (SINV), a mosquito-borne virus that causes rash and arthritis, has been causing outbreaks in humans every seventh year in northern Europe. To gain a better understanding of SINV epidemiology in Finland, we searched for SINV antibodies in 621 resident grouse, whose population declines have coincided with human SINV outbreaks, and in 836 migratory birds. We used hemagglutination-inhibition and neutralization tests for the bird samples and enzyme immunoassays and hemagglutination-inhibition for the human samples. SINV antibodies were first found in 3 birds (red-backed shrike, robin, song thrush) during their spring migration to northern Europe. Of the grouse, 27.4% were seropositive in 2003 (1 year after a human outbreak), but only 1.4% were seropositive in 2004. Among 2,529 persons, the age-standardized seroprevalence (1999-2003) was 5.2%; seroprevalence and incidence (1995-2003) were highest in North Karelia (eastern Finland). Grouse may contribute to the epidemiology of SINV in humans.

Prolonged survival of Puumala hantavirus outside the host: evidence for indirect transmission via the environment.

The capability of rodent-borne viruses to survive outside the host is critical for the transmission dynamics within rodent populations and to humans. The transmission of Puumala virus (PUUV) in colonized bank voles (Clethrionomys glareolus) was investigated and additional longevity studies in cell culture with PUUV and Tula (TULV) hantaviruses were performed. Wild-type PUUV excreted by experimentally infected donor bank voles was shown to be transmitted indirectly between rodents through contaminated beddings, and maintained its infectivity to recipient voles at room temperature for 12-15 days. In cell culture supernatants, PUUV and TULV remained infectious for 5-11 days at room temperature and up to 18 days at 4 degrees C, but were inactivated after 24 h at 37 degrees C. Interestingly, a fraction of dried virus was still infectious after 1 h at 56 degrees C. These results demonstrated that hantavirus transmission does not require direct contact between rodents, or between rodents and humans, and that the indirect transmission of PUUV through contaminated environment takes place among the rodents for a prolonged period of time. The results also have implications for safety recommendations for work with hantaviruses and for preventive measures.

Clinical and laboratory manifestations of Sindbis virus infection: prospective study, Finland, 2002-2003.

Sindbis virus (SINV) is widespread in Europe, Africa, Australia, and Asia, but clinical infection occurs as epidemics in a few geographically restricted areas. We recently proved, by virus isolation from patients, that SINV is the causative agent of Pogosta disease, a mosquito-borne rash-arthritis occurring as larger epidemics every seventh year in Finland. Altogether, 86 patients with serologically verified SINV infection were recruited to the present study during the 2002 outbreak. We now describe in detail the duration, incidence, and characteristics of different symptoms; hematological parameters; antibody kinetics; and presence of SINV in different tissue samples. SINV RNA detection or virus isolation from blood and/or skin lesions was successful in 8 patients. Immunoglobulin (Ig) M antibodies became detectable within the first 8 days of illness, and IgG antibodies became detectable within the first 11 days of illness. During the acute phase of Pogosta disease, the typical symptoms were arthritis, itching rash, fatigue, mild fever, headache, and muscle pain. The most notable finding was that, in 50% of the patients, joint symptoms lasted for >12 months.

Causative agent of Pogosta disease isolated from blood and skin lesions.

Pogosta disease is a mosquito-borne viral disease in Finland, which is clinically manifested by rash and arthritis; larger outbreaks occur in 7-year intervals. The causative agent of the disease has been suspected of being closely related to Sindbis virus (SINV). We isolated SINV from five patients with acute Pogosta disease during an outbreak in fall 2002 in Finland. One virus strain was recovered from a whole blood sample and four other strains from skin lesions. The etiology of Pogosta disease was confirmed by these first Finnish SINV strains, which also represent the first human SINV isolates from Europe. Phylogenetic analysis indicates that the Finnish SINV strains are closely related to the viral agents that were previously isolated from mosquitoes and that are related clinically similar diseases in nearby geographic areas.