Antigenic and genetic properties of viruses linked to hemorrhagic fever with renal syndrome.

Hemorrhagic fever with renal syndrome (HFRS) comprises a variety of clinically similar diseases of viral etiology that are endemic to and sporadically epidemic throughout the Eurasian continent and Japan. Although HFRS has not been reported in North America, viruses that are antigenically similar to HFRS agents were recently isolated from rodents in the United States. Examination and comparison of eight representative isolates from endemic disease areas and from regions with no known associated HFRS indicate that these viruses represent a new and unique group that constitutes a separate genus in the Bunyaviridae family of animal viruses.

Genetic variation of wild Puumala viruses within the serotype, local rodent populations and individual animal.

Reverse transcriptase polymerase chain reaction cloning and sequencing were used to determine the range of S gene/N protein variability in wild Puumala virus (PUU) strains and to study phylogenetic relationships between two groups of strains which originated from Finland and from European Russia. Analyses of the nucleotide and predicted amino acid sequences showed: (1) all PUU strains shared a common ancient ancestor; and (2) the more recent ancestors were different for the Finnish branch and the Russian branch of PUU strains. A cluster of amino acid substitutions in the N protein of Finnish strains was found; this cluster was located within a highly variable region of the molecule carrying B-cell epitopes (Vapalahti et al., J. Med. Virol., 1995, in press). Different levels of S gene/N protein diversity of PUU were revealed supporting the view of geographical clustering of genetic variants. Puumala virus from individual voles was found to be a complex mixture of closely related variants-quasispecies. The ratio of non-silent to silent nucleotide mutations registered in the S genes/N proteins of PUU quasispecies was 4- to 16-fold higher than that in Puumala virus strains, resulting in a more wide range of quasispecies N protein sequence diversity.

Clinical and serological diagnosis of Nephropathia epidemica, the mild type of haemorrhagic fever with renal syndrome.

The serological diagnosis of Nephropathia epidemica (NE), the mild European type of haemorrhagic fever with renal syndrome (HFRS), was studied by means of an indirect immunofluorescent antibody technique (IFAT) in a large outbreak in Finland (morbidity 1.4/1000 population). Acetone-fixed sections of lung of bank voles (Clethrionomys glareolus) naturally infected with Puumala virus served as antigen. Altogether 65 patients were followed serologically for up to 20 months. Serological results obtained by NE-IFAT were compared with the clinical diagnosis of NE. Of the 41 clinically accepted NE cases 40 were serologically positive. Use of the NE-IFAT serological test allowed the diagnosis to be made in seven patients for whom the clinical data were not sufficient for diagnosing NE. The antibody response in NE often appears to be slower than that against Hantaan virus. Practical recommendations are given for the clinical and serological diagnosis of the milder forms of HFRS.

Renal biopsy findings and clinicopathologic correlations in nephropathia epidemica.

A series of 126 adult patients with a serologically confirmed diagnosis of nephropathia epidemica (NE) were studied during the acute phase of the disease. In 86 cases, renal biopsy was performed. The severity of renal failure correlated slightly with blood inflammatory parameters and the degree of hematuria but not with the amount of proteinuria. The degree of hematuria correlated inversely with the level of thrombocytopenia. The most common histopathologic lesion was acute tubulointerstitial nephritis. Interstitial edema and inflammatory cell infiltrations were most usually present, followed by tubular epithelial and luminal alterations. Slight glomerular mesangial changes were present in 25% of the biopsy specimens. Except for hemorrhage in the outer renal medulla, the histologic lesions were relatively mild and unspecific. Interstitial hemorrhage should remind a pathologist of the possibility of NE. Tubular, interstitial and glomerular histologic damage were but vascular lesions were not associated with the clinical severity of renal failure. Glomerular alterations did not relate to the amount of urine protein excretion. Correlations, however, were so weak that in clinical work renal biopsy is usually not indicated for determination of the severity of renal failure in NE. Intrinsic renal events are probably important in the development of renal failure in NE.

Serological survey with the antigen of haemorrhagic fever virus with renal syndrome in small rodents in Slovakia.

Results of serological survey in small rodents with the antigen of haemorrhagic fever with renal syndrome (HFRS) virus indicate the existence of a natural focus of this virus in Slovakia. Antibodies were found in the following free-living rodent species: Clethrionomys glareolus, Apodemus agrarius, Apodemus sylvaticus, Pitymys subterraneus, Microtus arvalis and Microtus economus. A total 10 out of 120 (8.2%) small rodents trapped in investigated localities of Western and Eastern Slovakia had antibodies to the HFRS virus antigen as detected by complement fixation (CF) and/or immunofluorescence (IF) tests.

Haemorrhagic fever virus with renal syndrome in small rodents in Czechoslovakia.

The antigen of haemorrhagic fever with renal syndrome (HFRS) was detected in the lungs of the following free-living small rodents trapped in different localities in Eastern Slovakia: Clethrionomys glareolus (2 positive samples of 7), Apodemus flavicollis (1 sample of 24) and Apodemus agrarius (7 positive samples of 66). The virus was first identified by indirect fluorescent antibody (FA) staining using human convalescent serum from a case of epidemic nephropathy (NE) of Scandinavia. The lung suspensions selected according to positive immunofluorescence were inoculated by intramuscular (i.m.) route into suckling rats; the antigen prepared from the lungs of these rats by sucrose-acetone extraction reacted with the prototype human serum in complement-fixation (CF) reaction. The results of the latter assay were in good agreement with those of the indirect FA staining.

Tick-borne viruses in Finland.

Ixodes ricinus is the only one of six tick species reported from Finland found to carry viruses. It transmits tick-borne encephalitis and Uukuniemi viruses, and transmission of a Kemerovo group virus is suggested by antibody findings. Tick-borne encephalitis is common only in the SW-archipelago; it is also found near the SE-boarder but is very rare elsewhere. In contrast, Uukuniemi virus is common throughout the distribution area of I. ricinus, being commoner on the mainland than in the archipelago. Medium, large and small mammals participate in the cycle of tick-borne encephalitis virus, though birds are not excluded and apparently they act as host to the Uukuniemi virus. The encephalitis virus causes clinical illness in man, with cases limited mostly to the SW-archipelago; the disease is a relatively mild form of tick-borne encephalitis, with biphasic and meningeal symptoms dominating.

Mosquito-borne viruses in Finland.

Inkoo virus, the Finnish representative of the California group, was isolated from a pool of Aedes communis/punctor. It is distinguishable from Tahyna, California encephalitis, Trivittatus and Melao viruses, but seems to be antigenically related to the Jamestown Canyon virus. The prevalence of Inkoo antibodies increases towards the north in both human beings (16% to 69%) and cows (37% to 88%). Inkoo antibodies are common also in other mammals of large size (reindeer, moose, foxes), less frequent in snow hares, rare in hazel grouse and not detected in other birds and small mammals. Some show hare serum samples react with Inkoo virus only in the hemmaglutination inhibition test suggesting the existence of another California group virus in Finland. In addition, antibodies against some other mosquito-borne viruses have been found in Finland. A Batai virus epizootic among cows may have occured in the early 1960's in southern coastal Finland, and some serological data point to the existence of alphaviruses in Finland. The overwintering mechanism of the Finnish mosquito-borne viruses is still unsolved.