A new Clethrionomys-derived hantavirus from Germany: evidence for distinct genetic sublineages of Puumala viruses in Western Europe

Puumala (PUU) viruses are the predominant etiologic agents of hantavirus infections in Europe. The most important reservoir is the bank vole, Clethrionomys glareolus (Cg), belonging to the subfamily Arvicolinae of the Muridae family. Here we report on the molecular characterization of the first rodent-derived sequence (PUU/Cg-Erft) from Germany. Comparison of the S and M segment coding regions revealed 92.5 and 92.8% identity, respectively, with PUU/H-9013, a human isolate from France. However, only 83.1% identity was found with the S segment of a previously reported PUU sequence from a German HFRS case (PUU/H-Berkel) indicating the co-existence of two distinct sublineages in Germany. Phylogenetic and alignment analyses of S and M segment coding regions enabled us to assign PUU viruses/sequences to at least six distinct genetic sublineages. Membership was defined by nucleotide sequence differences of < 8%, whereas a diversity of > 14% clearly outgrouped a virus/sequence. Based on S segment sequences the sublineage represented by Clethrionomys rufocanus-derived viruses from Japan diverged at a well supported node from the clade harbouring all Clethrionomys glareolus-derived European PUU viruses. A correlation between genetic relationship and geographic origin of PUU viruses was observed which may support a co-evolution of PUU viruses with distinct subspecies of their reservoir host.

A new picornavirus isolated from bank voles (Clethrionomys glareolus)

A previously unknown picornavirus was isolated from bank voles (Clethrionomys glareolus). Electron microscopy images and sequence data of the prototype isolate, named Ljungan virus, showed that it is a picornavirus. The amino acid sequences of predicted Ljungan virus capsid proteins VP2 and VP3 were closely related to the human pathogen echovirus 22 (approximately 70% similarity). A partial 5' noncoding region sequence of Ljungan virus showed the highest degree of relatedness to cardioviruses. Two additional isolates were serologically and molecularly related to the prototype.

The muskrat (Ondatra zibethicus) as a new reservoir for puumala-like hantavirus strains in Europe

We have used an indirect immunofluorescent assay (IFA) and reverse transcription-PCR (RT-PCR) to screen the sera and tissues of muskrats (Ondatra zibethica) caught in the northwest of Brandenburg and in the northeast of Saxony-Anhalt, Germany, for hantavirus infection. Kidney and/or lung tissue from 6 (3.1%, CI = 1.1-6.5%) out of 197 muskrats were found to be positive for genomic sequences of hantavirus by RT-PCR. We could also demonstrate that 14 (5%, CI = 2.9-8.7%) out of 266 muskrat's sera available for testing contained hantavirus-specific antibodies in IFA. Thus, a total of 8% of the investigated muskrat population was found to be positive for hantavirus infection by RT-PCR and IFA. None of the animals was found positive in both tests. Further analysis of the RT-PCR amplified fragments by genomic sequencing revealed sequences mostly related to the puumala (PUU) S segment sequence of the Hällnäs B1 hantavirus strain (97-99% similarity). Our data therefore demonstrate that Ondatra zibethicus serves as an additional reservoir for puumala-like hantavirus strains in Europe. The epidemiological implications of this finding for hantavirus infection in Europe and elsewhere are discussed.

A minority of seropositive wild bank voles (Clethrionomys glareolus) show evidence of current Puumala virus infection

Bank voles (Clethrionomys glareolus) serve as the reservoir for Puumala (PUU) virus, the aetiologic agent of nephropathia epidemica. The animals are believed to be persistently infected and the occurrence of serum antibodies is usually taken as an evidence of active infection. We found serum antibodies to PUU virus in 42 of 299 wild bank voles captured in a PUU virus endemic area. PUU virus RNA was demonstrated in lung specimens of 11 of these 42 animals and in 2 of them antigen was also found. Thus in the lungs of 31 of 42 seropositive animals neither PUU virus RNA nor antigen was detected. In 2 of 257 seronegative animals, lung specimens showed presence of PUU virus antigen and RNA. Isolation of PUU virus from lung tissue was successful in all 4 antigen-positive bank voles but in none of 16 tested antigen-negative animals. In conclusion, only a minority of bank voles with serum antibodies to PUU virus showed evidence of current infection.

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).

Cell culture adaptation of Puumala hantavirus changes the infectivity for its natural reservoir, Clethrionomys glareolus, and leads to accumulation of mutants with altered genomic RNA S segment

This paper reports the establishment of a model for hantavirus host adaptation. Wild-type (wt) (bank vole-passaged) and Vero E6 cell-cultured variants of Puumala virus strain Kazan were analyzed for their virologic and genetic properties. The wt variant was well adapted for reproduction in bank voles but not in cell culture, while the Vero E6 strains replicated to much higher efficiency in cell culture but did not reproducibly infect bank voles. Comparison of the consensus sequences of the respective viral genomes revealed no differences in the coding region of the S gene. However, the noncoding regions of the S gene were found to be different at positions 26 and 1577. In one additional and independent adaptation experiment, all analyzed cDNA clones from the Vero E6-adapted variant were found to carry substitutions at position 1580 of the S segment, just 3 nucleotides downstream of the mutation observed in the first adaptation. No differences were found in the consensus sequences of the entire M segments from the wt and the Vero E6-adapted variants. The results indicated different impacts of the S and the M genomic segments for the adaptation process and selective advantages for the variants that carried altered noncoding sequences of the S segment. We conclude that the isolation in cell culture resulted in a phenotypically and genotypically altered hantavirus.

The effect of cowpox virus infection on fecundity in bank voles and wood mice

Although epidemic infectious diseases are a recognized cause of changes in host population dynamics, there is little direct evidence for the effect of endemic infections on populations. Cowpox virus is an orthopoxvirus which is endemic in bank voles (Clethrionomys glareolus), wood mice (Apodemus sylvaticus) and field voles (Microtus agrestis) in Great Britain. It does not cause obvious signs of disease nor does it affect survival, but in this study we demonstrate experimentally that it can reduce the fecundity of bank voles and wood mice by increasing the time to first litter by 20-30 days. The pathogenic mechanisms causing this effect are at present not known, but this finding suggests that natural subclinical infection could have a considerable effect on the dynamics of wild populations.

Puumala and Dobrava viruses cause hemorrhagic fever with renal syndrome in Bosnia-Herzegovina: evidence of highly cross-neutralizing antibody responses in early patient sera

Hantavirus infection was diagnosed serologically by mu-capture IgM and IgG ELISAs in hemorrhagic fever with renal syndrome (HFRS) patients admitted to Tuzla Hospital, Bosnia-Herzegovina. The results indicated that more than one hantavirus caused the outbreak. To address the question of which hantavirus serotypes were involved, sequentially drawn sera were analyzed by focus reduction neutralization test (FRNT) for antibodies against Puumala, Hantaan, Dobrava, and Seoul hantaviruses. The data revealed that acute- or early convalescent-phase sera, even when drawn as late as 3 weeks after the onset of disease, could not be used for typing of the causative hantavirus; a significant number of these samples showed similar reactivity of neutralizing antibodies to several different hantavirus serotypes. Moreover, although several acute-phase sera showed the highest FRNT titer to Hantaan virus, convalescent sera from these patients in all cases showed high specificity for Puumala or Dobrava viruses. This phenomenon, interpreted as a cross-neutralizing primary antibody response, makes several earlier reports concerning causative agents of HFRS questionable. Serological examination of small rodents trapped in the endemic area identified Puumala- and Dobrava-like virus infections. RT-PCR and sequencing of rodent lung samples identified Dobrava virus in one yellow-necked field mouse (Apodemus flavicollis). Cross-FRNT data, using polyclonal rabbit antibodies, clearly confirmed Dobrava virus as a unique hantavirus serotype. In conclusion, the results revealed that both Puumala- and Dobrava-like viruses caused HFRS in Bosnia-Herzegovina, whereas no signs of Hantaan or Seoul virus involvement were found.

Community structure and prevalence of hantavirus infection in rodents: a geographic division of the enzootic area in far eastern Russia

The results of an extensive rodent trapping effort throughout the southern part of far eastern Russia and hantavirus antigen screening of tissues were used to develop a multifaceted approach for the geographic division of the enzootic territory of hantavirus. Four species of rodents (Apodemus agrarius, Apodemus peninsulae, Microtus fortis, and Clethrionomys rufocanus) comprised 88.5 percent of 10,595 captured rodents and 94.1 percent of 996 antigen-positive animals. Rodent fauna and the prevalence and distribution of hantavirus antigen-positive animals were compared among major biotic communities in the region. The species composition of the rodent communities and the predominant hantavirus reservoir species were used as criteria to define zones with similar enzootic characteristics.

High prevalence of hantavirus antibodies in bank voles (Clethrionomys glareolus) captured in the vicinity of households afflicted with nephropathia epidemica

Puumala virus, the causative agent of nephropathia epidemica (NE), occurs endemically in Europe and is spread mainly by the bank vole (Clethrionomys glareolus). In the vicinity of each of four households afflicted with NE, we studied rodents with regard to population density and prevalence of Puumala virus-specific antibodies. For each case area, a control area was randomly selected 10 km away, without regard to the presence of human settlement. During 6,000 trap nights, 328 rodents were caught, of which 299 were C. glareolus. The mean rodent densities of case and control areas were 6.6 and 3.7 animals per 100 trap nights (P < 0.001). The prevalence of serum antibodies was 15.9% in case areas compared with 5.6% in control areas (P < 0.05). In three of the case areas, where NE had occurred 3-10 weeks before trapping, the rodent density and seroprevalence were much higher than in the fourth area, where NE occurred 38 weeks before trapping. In conclusion, C. glareolus seropositive for Puumala virus occurred more frequently near households afflicted with NE than in control areas 10 km away.

Cowpox in British voles and mice

Serosurveys indicate that bank voles, field voles and woodmice are probably reservoir hosts of cowpox virus in western Europe, although virus has not yet been isolated from these species. In this study, bank voles, field voles, woodmice and laboratory mice were shown to be susceptible to combined intradermal and subcutaneous inoculation with 3-20 plaque-forming units (pfu) of cowpox virus. Bank and field voles, but not laboratory mice, were also susceptible to combined oral and nasal inoculation with 50 pfu. Few clinical signs were seen and virus was generally recovered only from inoculation sites. Bank voles were not susceptible to injection of ectromelia virus (5000 pfu) into the skin (as described above). These results provide information on which further pathogenesis and transmission studies can be based, and support the view that the orthopoxvirus antibody detected in British wild voles and woodmice indicates infection with cowpox virus. However, further investigation of the pathogenesis of cowpox in these species is needed to understand better the epidemiology of the disease.

Quasispecies in wild-type tula hantavirus populations

Tula virus (TUL) is a recently detected hantavirus carried by European common voles. Reverse transcriptase PCR cloning was used to study TUL S segment/N protein quasispecies. Both the distribution and character of mutations observed in three mutant spectra indicated limited selection at the protein level. At least 8% of the mutations were neutral or well tolerated; fixation of such mutations may play a role in TUL evolution in its natural host.

Isolation and characterization of Tula virus, a distinct serotype in the genus Hantavirus, family Bunyaviridae

A Vero E6 cell culture isolate of Tula virus (TUL), a hantavirus first detected in European common voles (Microtus arvalis and M. rossiaemeridionalis) by RT-PCR was obtained after initial passaging of TUL-infected vole lung samples in laboratory-colonized M. arvalis. TUL was defined as a classical serotype by a cross-focus-reduction neutralization test (FRNT) and was also shown to be distinct from other hantaviruses by haemagglutination inhibition assay. The sequences of S, M and partial L genome segments of the isolate were determined: the S segment was 99.9% identical to the original rodent-derived sequence. Serological evidence for a previous TUL infection was obtained from the serum of a blood donor living near a TUL focus in Moravia, Czech Republic, showing at least a 16-fold higher FRNT titre to TUL as compared to Puumala or other hantaviruses.

Characterization of Tula virus antigenic determinants defined by monoclonal antibodies raised against baculovirus-expressed nucleocapsid protein

Tula virus was recently discovered by RT-PCR in lung samples from European common voles (Microtus arvalis and M. rossiaemeridionalis). Since virus isolation attempts had been unsuccessful, no antigen was available for analysis or for use in immunoassays. To circumvent this, complete Tula virus nucleocapsid protein (bac-TUL-N) was expressed in recombinant baculovirus. Rodent antibody end-point titers to bac-TUL-N and to truncated N fragments indicated that the NH2-terminal region is the major antigenic target and revealed a high cross-reactivity to Puumala virus N. Immunizations with crude bac-TUL-N preparations evoked high antibody responses to native hantavirus N in Balb/c mice and six monoclonal antibodies (Mabs) were generated. Epitope mapping of the Mabs, based on a competitive assay, reactivities to truncated recombinant N fragments, and reactivity patterns to different hantavirus strains, identified five recognition sites on Tula virus N. One epitope, which was identified as specific for Tula virus, was located in a region of N which is highly variable among the hantaviruses (aa 226-293), and four epitopes were mapped to the NH2-terminal region of the protein (aa 1-61). One epitope was expressed only in Tula and Prospect Hill viruses, one epitope in Tula, Prospect Hill, Khabarovsk, and Sin Nombre viruses, while two epitopes were conserved in all examined hantaviruses carried by rodents within the subfamily Arvicolinae of the Muridae family.

Rodents, human remains, and North American hantaviruses: risk factors and prevention measures for forensic science personnel--a review

In 1993, a previously unrecognized hantavirus was identified as the cause for a severe form of respiratory distress later termed Hantavirus Pulmonary Syndrome (HPS). In the past two years, several distinct hantaviruses, of which many are pathogenic, have been found in rodent populations in the US. Rodents shed the virus in their saliva, urine, and feces. Humans usually become infected after inhaling either aerosolized droplets of urine or particulates contaminated with rodent excreta. Rodents, including those identified as hantavirus reservoirs, will often infest and disturb human remains. Forensic science personnel should recognize the potential HPS risks associated with rodent contaminated remains and consider using High Efficiency Particulate Air-filter respirators, disinfectants, and insecticides to minimize risks.

Distribution and genetic heterogeneity of Puumala virus in Sweden

Small mammals trapped in Sweden were analysed for specific antibody responses against three hantavirus serotypes and for the presence of viral antigen. To determine the genetic identity of viral RNA in lungs of seropositive bank voles (Clethrionomys glareolus), polymerase chain reactions and subsequent partial sequencing of both the M and S segments were employed. The sequences obtained were all identified as Puumala (PUU) virus, with a high degree of heterogeneity between the different geographical localities. Alignment of nucleotide and deduced amino acid sequences, together with phylogenetic analysis, showed that PUU viruses circulating in central Sweden were distinct from those in the northern region. The localization of the two distinct PUU virus genotypes was shown to correlate with the postglacial recolonization of Sweden by bank voles.

Khabarovsk virus: a phylogenetically and serologically distinct hantavirus isolated from Microtus fortis trapped in far-east Russia

Two hantavirus strains, MF43 and MF113, isolated from Microtus fortis trapped in the Khabarovsk region of far-eastern Russia, were analysed by direct nucleotide sequencing of PCR generated fragments of the M and S segments, by immunofluorescence and by focus reduction neutralization tests (FRNT). The nucleotide sequences revealed that the two isolates were closely related to each other but distinct from all other hantaviruses. Phylogenetic analysis of the M and S segments showed that the MF strains form a separate branch in the Hantavirus tree, positioned between the branches of Prospect Hill and Puumala viruses. The strains were shown to be serologically distinct from the other hantavirus serotypes by FRNT using immune rabbit sera. Puumala virus was the closest relative, both genetically and serologically. We propose that this new hantavirus serotype should be named Khabarovsk (KBR).

Vector-borne viral diseases in Sweden--a short review

Ockelbo disease, caused by a Sindbis-related virus transmitted to man by mosquitoes, was first described in the central part of Sweden in the 1960s as clusters of patients with fever, arthralgia and rash. An average annual rate of 30 cases was recorded in the 1980s but no cases have been diagnosed during the last few years. Nephropathia epidemica (NE) characterized by fever, abdominal pain and renal dysfunction has been known to cause considerable morbidity in Sweden during the last 60 years but the etiologic agent (Puumala virus) was not isolated until 1983. This virus's main reservoir is the bank vole (Clethrionomys glareolus). NE is endemic in the northern two thirds of Sweden where more than a hundred cases are diagnosed each year. Tick-borne encephalitis transmitted by Ixodes ricinus ticks is restricted to the archipelago and Lake M-alaren on the east coast close to Stockholm. Between 30 and 110 cases are diagnosed every year. Inkoo virus, a California encephalitis group virus, has been isolated from mosquitoes in Sweden. The antibody prevalence to Inkoo virus is very high in a normal population, but no disease has as yet been associated with this virus in Sweden. Among the vector-borne virus diseases imported to Sweden, dengue is the most important, with approximately 50 cases recorded every year.

Isla Vista virus: a genetically novel hantavirus of the California vole Microtus californicus

Prospect Hill virus (PH) was isolated from a meadow vole (Microtus pennsylvanicus) in 1982, and much of its genome has been sequenced. Hantaviruses of other New World microtine rodents have not been genetically characterized. We show that another Microtus species (the California vole M. californicus) from the United States is host to a genetically distinct PH-like hantavirus, Isla Vista virus (ILV). The nucleocapsid protein of ILV differs from that of PH by 11.1% and a portion of the G2 glycoprotein differs from that of PH by 19.6%. ILV antibodies were identified in five of 33 specimens of M. californicus collected in 1975 and 1994-1995. Enzymatic amplification studies showed that 1975 and 1994-1995 ILV genomes were highly similar. Secondary infection of Peromyscus californicus was identified in Santa Barbara County, California. A long-standing enzootic of a genetically distinct hantavirus lineage is present in California voles.

Molecular linkage of hantavirus pulmonary syndrome to the white-footed mouse, Peromyscus leucopus: genetic characterization of the M genome of New York virus

The complete M segment sequences of hantaviruses amplified from tissues of a patient with hantavirus pulmonary syndrome in the northeastern United States and from white-footed mice, Peromyscus leucopus, from New York were 99% identical and differed from those of Four Corners virus by 23%. The serum of this patient failed to recognize a conserved, immunodominant epitope of the Four Corners virus G1 glycoprotein. Collectively, these findings indicate that P. leucopus harbors a genetically and antigenically distinct hantavirus that causes hantavirus pulmonary syndrome.

Genetic variation in Tula hantaviruses: sequence analysis of the S and M segments of strains from Central Europe

Hantavirus carried by the European common vole Microtus arvalis from Moravia (Czech Republic) was analyzed by RT-PCR-sequencing and by reactivity with a panel of monoclonal antibodies (MAbs). Sequencing of the full-length S segment and the proximal part of the M segment showed that the virus belonged to genotype Tula (TUL) we discovered earlier in Microtus arvalis from Central Russia. This finding supported the concept of host dependence of hantaviruses. Phylogenetic analyses suggested a similar evolutionary history for S and M genes of TUL strains; thus far there is no evidence for reassortment in TUL. Geographic clustering of TUL genetic variants was observed and different levels of the genetic variability were revealed resembling those estimated for another hantavirus, Puumala (PUU). Comparison of the deduced N protein sequence from Russia and from Moravia showed that genetic drift in TUL occurred not only by accumulation of point mutations but also by the deletion of a nucleotide triplet. It encoded Ser252 which was located within a highly variable hydrophilic part of the N protein carrying B-cell epitopes and presumably forming a loop. Analysis of naturally expressed TUL N-antigen derived from lung tissue of infected voles with MAbs indicated antigenic heterogeneity among TUL strains.

Coexistence of several novel hantaviruses in rodents indigenous to North America

Three genetically distinct members of the Hantavirus genus have been detected in Nevada rodents by RT-PCR and nucleotide sequence analysis. These include Sin Nombre (SN), El Moro Canyon (ELMC), and Prospect Hill (PH)-like viruses which are primarily associated with Peromyscus maniculatus (deer mouse), Reithrodontomys megalotis (western harvest mouse), and Microtus spp. (voles), respectively. Although this region of the United States is ecologically diverse, rodents infected with different hantaviruses appear to coexist in several different geographical and ecological zones. In two widely separated states, Nevada and North Dakota, PH-like viruses are present in three different species of vole. In addition, ELMC-like virus has been detected in both R. megalotis and M. montanus (mountain vole). SN virus is a cause of hantavirus pulmonary syndrome throughout much of the United States. SN virus RNA is found in 12.5% of P. maniculatus in Nevada and eastern California. Two lineages of SN virus coexist in this region and differ from SN viruses originally found in infected rodents in New Mexico, Arizona, and Colorado. These data show the complexity of hantavirus maintenance in rodents. Distinct hantaviruses or virus lineages can coexist either in different or the same rodent species and in either different or the same geographic or ecological zones.

Genetic characterization of a new hantavirus detected in Microtus arvalis from Slovakia

A new hantavirus, called Malacky, has been identified in lung tissue specimens of a vole, Microtus arvalis, by the reverse transcriptase polymerase chain reaction (RT-PCR). The voles were trapped in a geographical area in Slovakia where hemorrhagic fever with renal syndrome (HFRS) is endemic in the human population. Sequence analysis of a major part of the S segment showed this virus to represent a new subtype within Tula, a new hantavirus genetic group defined very recently.