Antigenic difference between viral strains causing classical and mild types of epidemic hemorrhagic fever with renal syndrome in China

Monitoring Neutralization Property Change of Evolving Hantaan and Seoul Viruses with a Novel Pseudovirus-Based Assay

The Hantaan virus (HTNV) and Seoul virus (SEOV) mutants have accumulated over time. It is important to determine whether their neutralizing epitopes have evolved, thereby making the current vaccine powerless. However, it is impossible to determine by using traditional plaque reduction neutralization test (PRNT), because it requires large numbers of live mutant strains. Pseudovirus-based neutralization assays (PBNA) were developed by employing vesicular stomatitis virus (VSV) backbone incorporated with HTNV or SEOV glycoproteins (VSVΔG^*-HTNVG or VSVΔG^*-SEOVG). 56 and 51 single amino acid substitutions of glycoprotein (GP) in HTNV and SEOV were selected and introduced into the reference plasmid. Then the mutant pseudoviruses were generated and tested by PBNA. The PBNA results were highly correlated with PRNT ones with R² being 0.91 for VSVΔG^*-HTNVG and 0.82 for VSVΔG^*-SEOVG. 53 HTNV mutant pseudoviruses and 46 SEOV mutants were successfully generated. Importantly, by using PBNA, we found that HTNV or SEOV immunized antisera could neutralize all the corresponding 53 HTNV mutants or the 46 SEOV mutants respectively. The novel PBNA enables us to closely monitor the effectiveness of vaccines against large numbers of evolving HTNV and SEOV. And the current vaccine remains to be effective for the naturally occurring mutants.

Wild Rats, Laboratory Rats, Pet Rats: Global Seoul Hantavirus Disease Revisited

Recent reports from Europe and the USA described Seoul orthohantavirus infection in pet rats and their breeders/owners, suggesting the potential emergence of a “new” public health problem. Wild and laboratory rat-induced Seoul infections have, however, been described since the early eighties, due to the omnipresence of the rodent reservoir, the brown rat Rattus norvegicus. Recent studies showed no fundamental differences between the pathogenicity and phylogeny of pet rat-induced Seoul orthohantaviruses and their formerly described wild or laboratory rat counterparts. The paucity of diagnosed Seoul virus-induced disease in the West is in striking contrast to the thousands of cases recorded since the 1980s in the Far East, particularly in China. This review of four continents (Asia, Europe, America, and Africa) puts this “emerging infection” into a historical perspective, concluding there is an urgent need for greater medical awareness of Seoul virus-induced human pathology in many parts of the world. Given the mostly milder and atypical clinical presentation, sometimes even with preserved normal kidney function, the importance of simple but repeated urine examination is stressed, since initial but transient proteinuria and microhematuria are rarely lacking.

Dentin matrix protein 1 correlates with the severity of hemorrhagic fever with renal syndrome and promotes hyper-permeability of endothelial cells infected by Hantaan virus

Hantaviruses are the major causative agents of hemorrhagic fever with renal syndrome (HFRS) in humans, which is characterized by increased capillary permeability. Dentin matrix protein 1 (DMP1) has been shown to degrade components of the basal membrane and interendothelial junctions via matrix metalloproteinase-9. To study the changes of serum DMP1 in HFRS, we determined the concentration of DMP1 using sandwich enzyme-linked immunosorbent assay. We found that serum DMP1 concentrations increased significantly, and reached peak value during the oliguric phase and in the critical group in HFRS patients. Moreover, serum DMP1 concentrations were closely related to blood urea nitrogen, creatinine, cystatin C, and vascular endothelial growth factor (VEGF). We further explored the role of DMP1 in HTNV-infected human umbilical vein endothelial cells (HUVECs) model. Data from immunocytochemistry showed that VEGF and tumor necrosis factor-α (TNF-α) promoted the expression of DMP1 on HTNV-infected HUVECs. Results from transwell assays demonstrated that the permeability of HUVECs increased significantly after HTNV infection with the addition of DMP1, VEGF, and TNF-α. This study suggests that elevated DMP1 concentrations may be associated with disease stage, severity, and the degree of acute kidney injury. DMP1 is involved in the regulation of capillary permeability in HFRS caused by hantavirus infection.

Comparison of serological assays to titrate Hantaan and Seoul hantavirus-specific antibodies

BACKGROUND

Hantaan and Seoul viruses, in the Hantavirus genus, are known to cause hemorrhagic fever with renal syndrome (HFRS). The plaque reduction neutralization test (PRNT), as conventional neutralization test for hantaviruses, is laborious and time-consuming. Alternatives to PRNT for hantaviruses are required.

METHODS

In this study, the methods for Hantaan and Seoul viruses serological typing including microneutralization test (MNT), pseudoparticle neutralization test (PPNT) and immunofluorescence assay based on viral glycoproteins (IFA-GP) were developed and compared with PRNT using a panel of 74 sera including 44 convalescent sera of laboratory confirmed HFRS patients and 30 patients sera of non-hantavirus infection. Antibody titres and serotyping obtained with different methods above were analyzed by paired-t, linear correlation, McNemar χ² and Kappa agreement tests.

RESULTS

Antibody titres obtained with MNT₅₀, PPNT₅₀ and IFA-GP were significantly correlated with that obtained with PRNT₅₀ (p < 0.001). GMT determined by PPNT₅₀ was statistically higher than that determined by PRNT₅₀ (p < 0.001), while GMT determined by MNT₅₀ and IFA-GP were equal with (p > 0.05) and less than (p < 0.001) that obtained with PRNT₅₀ respectively. Serotyping obtained with MNT₅₀ and PRNT₅₀, PPNT₅₀ and PRNT₅₀ were highly consistent (p < 0.001), whereas that obtained with IFA-GP and PRNT₅₀ were moderately consistent (p < 0.001). There were no significant differences for serotyping between PRNT₅₀ and MNT₅₀, as well as PRNT₅₀ and PPNT₅₀ (p > 0.05). IFA-GP was less sensitive than PRNT₅₀ and MNT₅₀ for serotyping of hantaviruses infection (p < 0.05). However, for 79.5% (35/44) samples, serotyping determined by IFA-GP and PRNT₅₀ were consistent.

CONCLUSIONS

MNT₅₀ and PPNT₅₀ both can be used as simple and rapid alternatives to PRNT₅₀, and MNT₅₀ is more specific while PPNT₅₀ is more sensitive than other assays for neutralizing antibody determination. So far, this work has been the most comprehensive comparison of alternatives to PRNT.

Prevalence of hemorrhagic fever with renal syndrome in Qingdao City, China, 2010-2014

Hemorrhagic fever with renal syndrome (HFRS) was considered to be transmitted by Apodemus agrarius and Rattus norvegicus, the principal animal hosts of Hantaan virus and Seoul virus, respectively. The aim of this study is to determine the correlation of HFRS incidence with capture rate and hantavirus infection rate of rodent species in Qingdao City, China. We collected HFRS patients' information and captured field and residential rodents in Qingdao City, China from 2010 to 2014. The correlations of HFRS incidence to rodent capture rate and hantavirus infection rate of rodents were analyzed statistically. The main findings of this study are that the high HFRS incidence (19.3/100,000) is correlated to the capture rate of field Mus musculus (p = 0.011, r = 0.037); but surprisingly it did not correlated to the capture rate of the principal rodent hosts Apodemus agrarius and Rattus norvegicus and the hantavirus infection rate of these rodent species in the field or residential area. These novel findings suggest that Mus musculus, a nontraditional animal host of hantavirus may play an important role in hantavirus transmission in Qingdao City.

Isolation and characterization of hantaviruses in Far East Russia and etiology of hemorrhagic fever with renal syndrome in the region

Hemorrhagic fever with renal syndrome (HFRS) is a serious public health issue in Far East Russia. Two different hantaviruses were isolated from rodents captured in the Khabarovsk region: Amur virus (AMRV; Khekhtsir/AP209/2005 strain from Apodemus peninsulae) and Hantaan virus (HTNV; Galkino/AA57/2002 strain from A. agrarius). Genetic analysis of the new isolates revealed that the M and L segments were apparently different between AMRV and HTNV, but S segments of the two viruses were closer. The antigenicities of AMRV, HTNV, and Seoul virus (SEOV) were differentiated by cross-neutralization. Serological differential diagnoses of 67 HFRS patients in the Prymorsky and Khabarovsk regions of Far East Russia were conducted using a neutralization test. The results revealed that the major cause of HFRS varied with location in Far East Russia: SEOV for Vladivostok city in the Prymorsky region, AMRV in rural areas of the Primorsky region, and probably HTNV for the Khabarovsk region.

Rodent-borne hantaviruses in Cambodia, Lao PDR, and Thailand

In order to evaluate the circulation of hantaviruses present in southeast Asia, a large scale survey of small mammal species was carried out at seven main sites in the region (Cambodia, Lao People's Democratic Republic, and Thailand). Small scale opportunistic trapping was also performed at an eighth site (Cambodia). Using a standard IFA test, IgG antibodies reacting to Hantaan virus antigens were detected at six sites. Antibody prevalence at each site varied from 0 to 5.6% with antibodies detected in several rodent species (Bandicota indica, B. savilei, Maxomys surifer, Mus caroli, M. cookii, Rattus exulans, R. nitidius, R. norvegicus, and R. tanezumi). When site seroprevalence was compared with site species richness, seropositive animals were found more frequently at sites with lower species richness. In order to confirm which hantavirus species were present, a subset of samples was also subjected to RT-PCR. Hantaviral RNA was detected at a single site from each country. Sequencing confirmed the presence of two hantavirus species, Thailand and Seoul viruses, including one sample (from Lao PDR) representing a highly divergent strain of Seoul virus. This is the first molecular evidence of hantavirus in Lao PDR and the first reported L segment sequence data for Thailand virus.

Hantavirus infections in humans and animals, China

Hemorrhagic fever with renal syndrome (HFRS) is a serious public health problem in the People's Republic of China. Although 7 sero/genotypes of hantaviruses have been found in rodents, only Hantaan virus (carried by Apodemus agrarius mice) and Seoul virus (carried by Rattus norvegicus rats) reportedly cause disease in humans. During 1950-2007, a total of 1,557,622 cases of HFRS in humans and 46,427 deaths (3%) were reported in China. HFRS has been reported in 29 of 31 provinces in China. After implementation of comprehensive preventive measures, including vaccination, in the past decade in China, incidence of HFRS has dramatically decreased; only 11,248 HFRS cases were reported in 2007. Mortality rates also declined from the highest level of 14.2% in 1969 to ?1% during 1995-2007. However, the numbers of HFRS cases and deaths in China remain the highest in the world.

Genetic analysis of hantaviruses carried by reed voles Microtus fortis in China

To gain more insights into the epidemiology of hantaviruses in China, the hantaviral S, M and L segment sequences were recovered from two Microtus fortis captured in Shenyang and four M. fortis trapped in Yuanjiang in China. Genetic analysis revealed that Shenyang sequences are closely related to the sequences of Fusong strains of Vladivostok virus (VLAV). Interestingly, the complete S segment and partial L segment sequences from Yuanjiang were quite distinct from those of Shenyang and Fusong strains, with up to 18% nucleotide (nt) and 5% amino acid (aa) sequence divergences. The partial M segment sequences (nt 2676-3650) from Yuanjiang were even more divergent from Shenyang and Fusong sequences (>20% and 8%, respectively). On the phylogenetic trees based on the S and partial M and L segment sequences, the Shenyang strains grouped together with Fusong strains. In contrast, four Yuanjiang sequences formed a distinct group that was a sister taxon to the Vladivostok-Fusong-Shenyang group. Our data indicated that the virus carried by M. fortis in Shenyang belong to VLAV. The newly characterized sequences from Yuanjiang might represent a novel distinct hantavirus species. Our results also demonstrated the great genetic diversity and complexity of the M. fortis-associated hantaviruses in China.

Genetic characterization of hantaviruses isolated from Guizhou, China: evidence for spillover and reassortment in nature

To gain more insights into the epidemiology of hantaviruses in the Guizhou province, China, rodents were captured in Guizhou during the period from 2001 to 2003. In addition, serum sample was collected from one patient. Virus isolation was attempted from human serum and rodent samples. Four hantaviruses were isolated successfully in cell culture from one human, two A. agrarius, and one R. norvegicus. The nucleotide sequences for the entire S and M and partial L segment were determined from these four isolates as well as six viruses isolated in 1980s. Phylogenetic analysis revealed that the S segment from all isolates belong to the Hantaan virus (HTNV) clade, regardless of the sources from which they were derived. According to the S sequences, these viruses could be divided into three distinct phylogroups, showing geographical clustering. Analysis of the entire M and the partial L segment sequences demonstrated that 8 out of the 10 isolates belong to the HTNV clade. However, two isolates (CGRn8316 and CGRn9415) isolated from R. norvegicus belong to the Seoul virus (SEOV) clade. In addition, these two isolates were distinct from other known members of SEOV clade. Together, the data suggest that at least three groups of HTNV are co-circulating and one new variant of SEOV may be present in Guizhou. Our results also suggest that HTNV from A. agrarius spilled over to R. norvegicus and natural reassortment between HTNV and SEOV occurred during or after the spillover.

Isolation and genetic characterization of hantaviruses carried by Microtus voles in China

To gain more insights into hantavirus distribution in China, Microtus fortis were caught in Jilin province and M. maximowiczii in the Inner Mongolia Autonomous Region. Hantavirus specific RNA was detected by RT-PCR in 3 out of 26 M. fortis and 5 out of 64 M. maximowiczii. Two hantaviruses (Fusong-Mf-682 and Yakeshi-Mm-59) were isolated successfully in cell culture and their S and M segment nucleotide sequences were determined. Phylogenetic analysis of the S and M segment sequences revealed that the Mf-originated strains from Fusong were closely related to Vladivostok hantavirus (VLAV) with 99% nucleotide identity, but differed from the Yakeshi-Mm strains, with an amino acid divergence of more than 8.8% for the N protein and 11.8% for the GnGc proteins. Yakeshi-Mm strains were closely related to the Khabarovsk hantavirus (KHAV) isolated earlier from M. fortis in Khabarovsk, with an amino acid sequence identity of more than 98.4% for the S segment and 95.6% for the M segment. On phylogenetic trees, Yakeshi-Mm strains clustered together with KHAV and Topografov virus (TOPV) carried by Lemmus sibiricus. The results suggest that the hantavirus carried by M. fortis in China belongs to VLAV type and should be considered as a distinct hantavirus species. They also suggest that M. fortis is the natural host of VLAV (including Fusong-Mf strains), whereas M. maximowiczii is the natural host of KHAV including Yakeshi-Mm strains. Thus, in addition to Hantaan, Seoul, Dabieshan and Puumala-like Hokkaido viruses, at least two other hantaviruses, namely KHAV and VLAV, are circulating in China.

Detection of phylogenetically distinct Puumala-like viruses from red-grey vole Clethrionomys rufocanus in China

In order to investigate whether Puumala virus (PUUV) or PUUV-like virus is present in China, Clethrionomys rufocanus and C. rutilus were captured in the Jilin province during the spring and autumn of 2002-2003 for detection of PUUV viral RNA by RT-PCR and confirmation of PUUV-positive antigens by an immunofluorescence assay. PUUV-positive RNA was identified in six out of 121 C. rufocanus but not in any of the 41 C. rutilus. Complete S and partial M sequences (nt 1,316-1,598 and 2,687-3,089) were amplified by RT-PCR directly from some of the antigen positive lung tissues and subjected to nucleic acid sequencing. It was found that the Chinese PUUV-like viruses were related most closely with the PUUV strains with 77.7-81.7% identity at the nucleotide level and 91.7-97% identity at the amino acid level for S segment, and with 77-78.8% identity at the nucleotide level and 91.5-92.6% identity at the amino acid level for the partial M segment (nt 1,316-1,598). Genetic analysis indicated that the Chinese PUUV-like viruses shared the highest level of identity with the viruses which circulate in C. rufocanus in the Far East region of Russia with 85.1-87.4% identity at the nucleotide level and 95.9% identity at the amino acid level for the partial M segment (nt 2,687-3,089), respectively. Phylogenetic analysis revealed that the Chinese PUUV-like viruses are distinct from those identified from Japan, South Korea, Europe or Russia. These results indicate that PUUV-like virus is present in China in addition to Hantaan, Seoul and Dabieshan viruses.

Isolation and characterization of hantavirus carried by Apodemus peninsulae in Jilin, China

To provide a better understanding of hantavirus epidemiology in China, Korean field mice (Apodemus peninsulae) and striped field mice (Apodemus agrarius) were captured in Jilin province, China, where haemorrhagic fever with renal syndrome (HFRS) is endemic. Hantavirus antigens were detected in eight of the 130 A. peninsulae individuals and in four of the 193 A. agrarius individuals by using an immunofluorescence assay. Partial S and M segments were amplified from all of the antigen-positive samples. Furthermore, two hantaviruses (CJAp89 and CJAp93) were isolated successfully in cell culture and the entire S and M segments were amplified from one of them (CJAp93). Phylogenetic analysis of these sequences (partial or complete) showed that hantaviruses carried by A. peninsulae and A. agrarius form two distinct lineages, although viruses carried by A. peninsulae are similar to those isolated previously from A. agrarius in China and from HFRS patients in Russia. However, the viruses detected in A. peninsulae in China are genetically different from those detected in A. peninsulae in other countries. These data suggest that A. peninsulae is also a natural host for HTNV in north-eastern China.

Genetic and antigenic characterization of the Amur virus associated with hemorrhagic fever with renal syndrome

The genetic and antigenic characteristics of the Amur (AMR) and Far East (FE) virus lineages, which are both within the genus Hantavirus, were studied. Representative viruses, H5 and B78 for AMR and Bao 14 for FE, were used. The entire small (S) and medium (M) segments, except for the 3'- and 5'-ends, were sequenced. The deduced amino acid sequences of AMR had 96.7 and 92.0-92.2% identities with the Hantaan (HTN) virus in the S and M segments, respectively. The amino acid sequences of FE had 99.1 and 97.9% identities in the S and M segments, respectively. The three viral strains and HTN virus had similar binding patterns to a panel of monoclonal antibodies (MAbs), except that one MAb did not bind AMR. However, sera from Apodemus peninsulae, naturally infected with AMR virus, neutralized homologous viruses at 1:160 to 1:320 dilutions and HTN at 1:20 to 1:40 dilutions. The anti-AMR serum neutralized homologous viruses at a 1:80 dilution and HTN at a 1:40 dilution. The anti-HTN serum did not neutralize AMR (<1:40 dilution), although it had a high neutralizing titer (1:320) against the homologous virus. Therefore, we suggest that AMR virus may constitute a distinct serotype within the genus Hantavirus.

Epizootiological and epidemiological study of hantavirus infection in Japan

Epizootiological surveys on hantavirus infections in rodents were carried out in various areas of Japan, including the four major islands of Hokkaido, Honshu, Shikoku, and Kyushu from 2000 to 2003. A total of 1,221 rodents and insectivores were captured. Seropositive animals were found in Apodemus (A.) speciosus (5/482, 1.0%), Rattus (R.) norvegicus (4/364, 1.1%), R. rattus (3/45, 6.7%), and Clethrionomys (C.) rufocanus (7/197, 3.6%). The partial S segment was amplified from one seropositive R. rattus captured at Hakodate. The nucleotide sequence showed 96% identity with the Seoul virus (SEOV) prototype strain SR-11. In addition, we conducted an epidemiological survey on human hantavirus infection in a high-risk population, the personnel of the Japan Ground Self-defense Force on Hokkaido. One out of 207 human blood samples was positive for anti-hantavirus antibody by IFA, ELISA, and WB analysis. The result of the serotype specific ELISA indicates that this individual acquired SEOV infection. This study indicates that A. speciosus, R. norvegicus, R. rattus, and C. rufocanus carry hantaviruses as the reservoir animals in Japan. Infected R. rattus and R. norvegicus in port areas could be the sources of human SEOV infection and a threat to travelers and individuals working in seaports.

Comparison of nucleotide sequences of M genome segments among Seoul virus strains isolated from eastern Asia

The nucleotide sequences of the M genome segments of three Seoul virus strains (KI strains) which were isolated from urban rats inhabiting the same enzootic focus between 1983 and 1988 were compared. The viral cDNAs were amplified by PCR and were directly sequenced. The nucleotide sequences of KI strains were extremely homologous regardless of isolation year (less than 10 substitutions in 3651 nucleotides, less than 4 substitutions in 1133 amino acids). In addition, the nucleotide sequence of the KI strain isolated in 1983 (KI-83-262) was also quite similar to that of other Seoul viruses, which were isolated from laboratory rats in Japan (strain SR-11, 98.1% and B-1 strain, 96.5%), from an urban rat in Korea (Seoul 80-39, 96.5%) and from an urban rat in China (R22 strain, 93.4%). All possible N-glycosylation sites in the deduced amino acid sequences were conserved among all Seoul viruses examined. The nucleotide and amino acid sequences of Seoul virus strains were highly conserved although they were isolated from various districts of eastern Asia. These results indicate the genetic stability of Seoul virus strains maintained under a natural environment and the homology of Seoul viruses isolated from various districts of eastern Asia. The relationship among Seoul virus strains isolated from eastern Asia was compared by phylogenetic analysis.

A novel mu-capture enzyme-linked immunosorbent assay based on recombinant proteins for sensitive and specific diagnosis of hemorrhagic fever with renal syndrome

Hantavirus nucleocapsid protein has recently been identified as a major antigen inducing an early and long-lasting humoral immune response in patients with hemorrhagic fever with renal syndrome. A mu-capture enzyme-linked immunosorbent assay utilizing recombinant nucleocapsid proteins of Hantavirus strains Hantaan 76-118 (Hantaan serotype) and CG 18-20 (Puumala serotype) as diagnostic antigens and specific monoclonal antibodies as the detection system has been developed. Histidine-tailed recombinant proteins were expressed in Escherichia coli and purified in a single step by affinity chromatography on a nickel-chelate resin. The assay was evaluated with a panel of sera from patients with hemorrhagic fever with renal syndrome originating from various geographic regions. The overall sensitivity of the mu-capture enzyme-linked immunosorbent assay (both recombinant antigens) was 100%, and its specificity was also found to be 100%. Immunoglobulin M antibodies were detected as early as on day 3, and maximum titers were obtained between days 8 and 25 after onset of the disease. The assay was regularly found to be positive within 3 to 4 months but in some cases up to 2 years after the acute phase of the disease.

Use of recombinant nucleocapsid proteins of the Hantaan and nephropathia epidemica serotypes of Hantaviruses as immunodiagnostic antigens

Hantavirus nucleocapsid protein has previously been identified as the major antigen recognized by the humoral immune response in hemorrhagic fever with renal syndrome (HFRS). It was therefore considered to be a suitable antigen for the development of rapid and reliable immunodiagnostic assays. Genes encoding the nucleocapsid proteins of two Hantavirus strains, one of the Puumala serotype [nephropathia epidemica virus (NEV)] and the other of the Hantaan serotype were expressed in E. coli, and the expression products were used as diagnostic antigens in solid-phase enzyme immunoassays. The assays were used to detect IgG- and IgM-antibodies in sera of HFRS patients originating from different geographic regions (China, Germany, Greece, Yugoslavia, Scandinavia). ELISA was highly sensitive and proved to be superior to the indirect immunofluorescence assay. Both antigens were necessary to diagnose all HFRS cases originating from the different countries. Most of the sera revealed a predominant reactivity with either 1 of the 2 antigens, allowing the characterization of the etiologic virus as Hantaan-like or NEV-like. The results of the analysis of sera obtained from China and Greece suggested that the Hantaviruses prevalent in these countries are closely related to the Hantaan serotype. In contrast, an NEV-like reactivity was observed in Central and Northern European patients. In the sera of Yugoslav patients both reactivity patterns were found, suggesting that both virus types occur in the Balkan region.

Development and application of protein G antibody assay for the detection of antibody to hantavirus

A new serodiagnostic method designated protein-G antibody assay (PGA) was developed for detection of hantavirus infection in various species of animals. The assay procedure includes reacting the sera with hantavirus-infected cells on glass slides, followed by incubation of biotinylated protein G and amplification with the avidin-biotinylated peroxidase complex. Specific antibody in rabbit, rat, mouse and Mongolian gerbil serum was detected by this method. The PGA titres were similar to those of the neutralization titre. In the sera of Mongolian gerbils infected with strain SR-11, antibody was first detected 10 days post infection, and the titre increased to 1:256 at 18 days post-infection. PGA was evaluated using sera of urban rats (Rattus norvegicus) captured in an endemic area of hantavirus infection. The negative (much less than 1:1, 24/62, 38.7%) and positive groups (much greater than 1:16, 38/62, 61.3%) were clearly distinguished. PGA titres were closely related to IFA titres in the sera. Two of 10 sera from Clethrionomys rufocanus and one from Apodemus speciosus captured in the same endemic area were positive to both PGA and IFA. These data indicate that PGA is a simple and useful method for seroepizootiological surveys of hantavirus infection, especially in wild rodent reservoirs.

Haemorrhagic fever with renal syndrome, virological and epidemiological aspects

Haemorrhagic fever with renal syndrome (HFRS) is characterized by fever, headache, abdominal pain, renal dysfunction and various haemorrhagic manifestations. The viruses causing HFRS all belong to the Hantavirus genus in the Bunyaviridae family. At least three of the different hantaviruses are associated with human disease: Hantaan, Seoul, and Puumala viruses. HFRS is endemic in a belt from Norway in the west, through Sweden, Finland, the Soviet Union, China, Korea to Japan in the east. The clinical severity of HFRS varies throughout this belt. A severe form with haemorrhagic manifestations and significant lethality (Korean haemorrhagic fever--caused by Hantaan and Seoul virus) occurs in Asia, while a milder form (nephropathia epidemica caused by Puumala virus) with less haemorrhagic manifestations and no or low lethality is found in Europe. All hantaviruses are spread by rodents where the major route of transmission to man is via aerosol from rodent urine, saliva and faeces. Although HFRS occurs with the same clinical picture in children as in adults both incidence rates and antibody prevalence rates are very low in children under 10 years. Men of working age make up the bulk of clinical cases.

Antibody-dependent enhancement of hantavirus infection in macrophage cell lines

Antibody-dependent enhancement (ADE) of hantavirus infections (strains Hantaan 76-118 and SR-11) was studied using macrophage-like cell lines (J774.1, P388D1, and U937). Significantly higher virus titers (1,000 to 4,000 FFU/ml) were obtained by pretreatment of the virus with immune serum as compared to normal serum (less than 20 FFU/ml). Monoclonal antibodies (MAbs) to strain Hantaan 76-118 were employed to determine the antigenic determinants responsible for the ADE activity. ADE of the infection occurred with MAbs to both G1 and G2 envelope glycoproteins, but not with MAbs to nucleocapsid protein. Antigenic determinants related to haemagglutination or virus neutralization were found to cause ADE of the infection.

Protective role of antigenic sites on the envelope protein of Hantaan virus defined by monoclonal antibodies

To investigate the role of Hantaan virus envelope glycoprotein in infection, a panel of monoclonal antibodies (MAbs) was examined in vitro with several serological tests and in vivo by passive transfer experiments in mice. An antigenic site, specific for the inhibition of infected cell focus was detected with the focus inhibition neutralization test (FINT), in addition to the neutralization related antigenic sites, which were revealed by the ordinary focus reduction neutralization test (FRNT). Suckling mice were given the MAbs by passive transfer followed by lethal Hantaan virus challenge. All neutralizing MAbs detected by either FRNT or FINT protected all mice from lethal infection, confirming the importance of the antigenic sites as a protective antigen. Mice given non-neutralizing MAbs by passive transfer, however, began to die earlier than the control group; mean time to death (18.2 +/- 2.1 to 21.5 +/- 2.8 days) being significantly shorter than that of the control group (25.8 +/- 1.8, p less than 0.01, Mann-Whitney, U probability test). Virus titers in brains of mice which died early, were about 10 times higher than those of control mice. These results indicated the early death phenomenon of mice which was mediated by the anti-virus antibody.

Molecular characterization and expression of glycoprotein gene of Hantavirus R22 strain isolated from Rattus norvegicus in China

A cDNA containing the complete open reading frame of the M genome segment of Hantavirus R22 strain isolated from Rattus norvegicus in China, was amplified by polymerase chain reaction (PCR), and then cloned. The M segment is 3656 nucleotides in length with a predicted region of 3402 bases encoding a precursor glycoprotein of 1134 amino acids subsequently processed into viral glycoproteins 1 and 2 (G1 and G2). A strain comparison between R22 and SR11 (isolated from a rat in Japan), and Hantaan 76-118 (isolated from Apodemus in Korea), and Hallnas B1 (isolated from a bank vole in Sweden) revealed 95%, 74%, and 53% homologies at the deduced amino acid sequence level respectively. This suggests that the rodent host species may be a more important determinant of genetic relationships than geographic proximity. Six potential asparagine linked glycosylation sites (five in G1 and one in G2) were identified, and among them all are conserved in SR11, five in Hantaan virus and four in Hallnas B1 virus. Although different degrees of homology exist among these four viruses at amino acid sequence level, more than 90% of the cysteine residues are conserved, suggesting that structural homology may be very strong between the Hantaviruses. Genetic differences in the M segment genome of R22 and SR11 viruses, within the same serotype viruses, were found as random coding changes; some limited to single amino acids, others in clusters. A recombinant vaccinia virus that contained the fully activated M segment cDNA of R22 was constructed. This recombinant virus expressed two glycoproteins G1 and G2 identical to R22 virus G1 and G2 in molecular weight, cleavage pattern and cellular immunofluorescent patterns.

Distribution of hantavirus serotypes Hantaan and Seoul causing hemorrhagic fever with renal syndrome and identification by hemagglutination inhibition assay

An epidemiologic evaluation of patients with hemorrhagic fever with renal syndrome from different locations in the People's Republic of China was conducted to define the prevalence of two Hantavirus serotypes, Seoul (SEO) and Hantaan (HTN). Serum specimens were collected between 5 and 14 days after the onset of illness and were tested for antibodies by both hemagglutination inhibition (HI) and plaque reduction neutralization (PRN). By the HI test, the geometric mean titer (GMT) of antibodies to SEO in the sera from individuals from Kaifeng City of Henan Province was five times higher than that to HTN. In contrast, by the HI test, the sera from individuals from Jiande County of Zhejiang Province had a GMT of antibodies to HTN that was seven times higher than that to SEO. In the sera from individuals from Shanghai, only a twofold difference was observed in HI antibody titers to the two hemagglutinins by the HI test, with that to HTN being higher than that to SEO. By the PRN test, the GMT ratios of antibody between HTN and SEO strains from individuals in Kaifeng, Jiande, and Shanghai were found to be 1:13, 14:1, and 2:1 respectively. A close correlation (r = 0.8219) and concordance rate (78.3%) were observed between the PRN and HI tests for the identification of the serotypes of individual cases of hemorrhagic fever with renal syndrome. The hantavirus serotypes from individuals in Kaifeng and Jiande were identified as predominantly SEO and HTN, respectively, and those from individuals in Shanghai had an indeterminant serotype defined by these two techniques. The HI test appears to be a simple and reliable way of determining the predominant hantavirus that causes HFRS in a given geographic area.

Monoclonal antibodies to three strains of hantaviruses: Hantaan, R22, and Puumala

Thirty hybrid cell lines that produce monoclonal antibodies to three strains of hantaviruses have been generated and characterized. One clone specific to Hantaan 76-118 strain, four clones specific to Rattus strains and one clone specific to Puumala virus have been identified. Most of the monoclones produced antibodies specific to nucleoproteins. Only two monoclones were found to produce glycoprotein specific, neutralizing antibodies. The immunofluorescent (IFA) staining patterns of the monoclonal antibodies show consistent correlation with viral protein specificities as described for other hemorrhagic fever viruses. Cross-reactivity studies with hantaviruses tested demonstrate conserved antigenic sites on nucleoproteins among these hantaviruses tested. Puumala specific monoclones, produced for the first time, reveal both conserved and strain specific sites on the viral nucleoproteins of the Scandinavian virus.

Antigenic subunits of Hantaan virus expressed by baculovirus and vaccinia virus recombinants

Baculovirus and vaccinia virus vectors were used to express the small (S) and medium (M) genome segments of Hantaan virus. Expression of the complete S or M segments yielded proteins electrophoretically indistinguishable from Hantaan virus nucleocapsid protein or envelope glycoproteins (G1 and G2), and expression of portions of the M segment, encoding either G1 or G2 alone, similarly yielded proteins which closely resembled authentic Hantaan virus proteins. The expressed envelope proteins retained all antigenic sites defined by a panel of monoclonal antibodies to Hantaan virus G1 and G2 and elicited antibodies in animals which reacted with authentic viral proteins. A Hantaan virus infectivity challenge model in hamsters was used to assay induction of protective immunity by the recombinant-expressed proteins. Recombinants expressing both G1 and G2 induced higher titer antibody responses than those expressing only G1 or G2 and protected most animals from infection with Hantaan virus. Baculovirus recombinants expressing only nucleocapsid protein also appeared to protect some animals from challenge. Passively transferred neutralizing monoclonal antibodies similarly prevented infection, suggesting that an antibody response alone is sufficient for immunity to Hantaan virus.

Hantavirus strains isolated from rodentia and insectivora in rural China differentiated by polymerase chain reaction assay

Polymerase chain reaction (PCR) assay and other techniques were applied to differentiate Hantavirus strains isolated from different animal hosts and geographic regions in China. Two groups of related strains, Hantaan and Seoul, have been classified by cross-neutralization, radioimmunoprecipitation (RIP), and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) assays. The molecular weights of glycoprotein 1 (G1) of Hantaan and Seoul viruses were 72k and 80k, whereas those of the nucleocapsid (N) and glycoprotein 2 (G2) remained the same, respectively. The PCR assay was used to differentiate these isolates using synthetic oligonucleotide primers selected from various regions of the M genome of 76118 and R22 strains. 76118-specific primers amplified only the RNAs extracted from Hantaan strains while R22-specific primers, the RNAs from Seoul strains. The PCR results for classification are consistent with those obtained by cross-neutralization, RIP and SDS-PAGE assays.

Virion proteins of viruses causing hemorrhagic fever with renal syndrome; monoclonal antibody analysis

SDS-polyacrylamide gel electrophoresis and Western blotting analysis by using 9 clones of monoclonal antibodies specific for hemorrhagic fever with renal syndrome (HFRS) viruses were carried out on the virion proteins of 17 strains of HFRS viruses isolated from different areas in Asia and different hosts such as Apodemus agrarius, Rattus norvegicus, domestic cat and HFRS patients. Polypeptide with apparent molecular weight about 50 kitodalton (Kd) could be detected in all 17 strains of HFRS viruses. On this polypeptide there are two different antigenic determinants and one of them might be genus specific.

Comparison of virulence between two strains of Rattus serotype hemorrhagic fever with renal syndrome (HFRS) virus in newborn rats

Two strains of hemorrhagic fever with renal syndrome (HFRS) virus from Rattus, SR-11 and KI-262, showed virtually identical antigenicity but differed from prototype strain Hantaan 76-118 (Apodemus origin) in a neutralization test. Wistar newborn rats inoculated intraperitoneally (i.p.) with SR-11, which was isolated from a laboratory rat associated with an outbreak of HFRS, developed clinical signs such as ataxia and limb paralysis and died at about 18 days after inoculation. The LD50 of SR-11 in 1-day-old rats was 10(1.2) focus-forming units (FFU). In contrast, the animals inoculated i.p. or intracerebrally with 10(4) FFU of KI-262, which was from a wild rat in a dumping-ground area--an enzootic focus where no human cases have been recorded--did not show any significant clinical signs. The susceptibility of rats to SR-11 fatal infection was age-dependent. Virus titers in brains, lungs, kidneys, and livers of the rats inoculated with SR-11 were significantly higher than those in the same organs of the animals infected with KI-262. Necrosis of neurons in the brain tissue occurred in the rats infected with SR-11, while it was mild in the animals infected with KI-262.

Immunoblot analysis of the serological response in Hantavirus infections

Sera from patients with nephropathia epidemica (NE) or Korean hemorrhagic fever (KHF) were tested for specific antibody response to antigens of Hällnäs virus and Hantaan virus strain 76-118. A Vero E6 derived cell line persistently infected with Hällnäs virus strain B1, and Vero E6 cells freshly infected with Hantaan virus type strain 76-118 were used as antigens in the immunofluorescence assay (IFA) and the immunoblot. Blots were prepared from whole cell lysates. The convalescent-phase sera of NE patients tested in this study regularly revealed a marked reaction with a 52 kilodalton (Kd) protein of Hällnäs virus and a 50 Kd protein of Hantaan virus. A convalescent serum from a patient with Korean hemorrhagic fever and a rat antiserum against Hantaan virus could recognize the 50 Kd band of Hantaan virus but showed no apparent reactivity with the 52 Kd component of Hällnäs virus in the standard dilutions. Some sera could additionally identify minor bands in the 55 Kd and/or 67 Kd region of the blots. A one-way cross reactivity between Hantaan and Hällnäs viruses was also evident from the results of the immunofluorescence assays in that NE convalescent sera reacted with both viruses, whereas KHF convalescent or anti-Hantaan sera gave strongly positive results with Hantaan virus but only faint reaction with Hällnäs virus.