Etiologic studies of epidemic hemorrhagic fever (hemorrhagic fever with renal syndrome)

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.

Epidemiology of Hantavirus infections in humans: a comprehensive, global overview

Hantaviruses comprise an emerging global threat for public health, affecting about 30,000 humans annually. Infection may lead to Hantavirus pulmonary syndrome (HPS) in the Americas and hemorrhagic fever with renal syndrome (HFRS) in the Europe and Asia. Humans are spillover hosts, acquiring infection primarily through the inhalation of aerosolized excreta from infected rodents and insectivores. Risk factors for infection include involvement in outdoor activities, such as rural- and forest-related activities, peridomestic rodent presence, exposure to potentially infected dust and outdoor military training; prolonged, intimate contact with infected individuals promotes transmission of Andes virus, the only Hantavirus known to be transmitted from human-to-human. The total number of Hantavirus case reports is generally on the rise, as is the number of affected countries. Knowledge of the geographical distribution, regional incidence and associated risk factors of the disease are crucial for clinicians to suspect and diagnose infected individuals early on. Climatic, ecological and environmental changes are related to fluctuations in rodent populations, and subsequently to human epidemics. Thus, prevention may be enhanced by host-reservoir control and human exposure prophylaxis interventions, which likely have led to a dramatic reduction of human cases in China over the past decades; vaccination may also play a role in the future.

A possible case of hantavirus infection in a Borneo orangutan and its conservation implication

BACKGROUND

Natural infection of hantavirus in orangutans has never been reported.

METHODS

Enzyme-linked immunosorbent assays (ELISA), Indirect immunofluorescence assay (IFA), and RT-PCR were used to diagnosis a suspected case in a pet orangutan in southern Taiwan.

RESULTS

Although the RT-PCR result was negative, the high IgG titer in the beginning and its dramatic drop after treatments suggested a recent Seoul-type hantavirus infection.

CONCLUSIONS

Hantavirus transmission and its potential damage to wild orangutans should not be overlooked.

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.

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.

Tick-borne rickettsial pathogens in ticks and small mammals in Korea

In order to investigate the prevalence of tick-borne infectious agents among ticks, ticks comprising five species from two genera (Hemaphysalis spp. and Ixodes spp.) were screened using molecular techniques. Ticks (3,135) were collected from small wild-caught mammals or by dragging/flagging in the Republic of Korea (ROK) and were pooled into a total of 1,638 samples (1 to 27 ticks per pool). From the 1,638 tick samples, species-specific fragments of Anaplasma phagocytophilum (1 sample), Anaplasma platys (52 samples), Ehrlichia chaffeensis (29 samples), Ehrlichia ewingii (2 samples), Ehrlichia canis (18 samples), and Rickettsia rickettsii (28 samples) were amplified by PCR assay. Twenty-one pooled and individual tick samples had mixed infections of two (15 samples) or three (6 samples) pathogens. In addition, 424 spleen samples from small captured mammals (389 rodents, 33 insectivores, and 2 weasels) were screened for selected zoonotic pathogens. Species-specific DNA fragments of A. phagocytophilum (110 samples), A. platys (68 samples), E. chaffeensis (8 samples), E. ewingii (26 samples), E. canis (51 samples), and Rickettsia sp. (22 samples) were amplified by PCR assay. One hundred thirty small mammals had single infections, while 4, 14, and 21 striped field mice (Apodemus agrarius) had mixed infections of four, three, and two pathogens, respectively. Phylogenetic analysis based on nucleotide sequence comparison also revealed that Korean strains of E. chaffeensis clustered closely with those from China and the United States, while the Rickettsia (rOmpA) sequences clustered within a clade together with a Chinese strain. These results suggest that these agents should be considered in differential diagnosis while examining cases of acute febrile illnesses in humans as well as animals in the ROK.

Hantavirus seropositivity in Israeli patients with renal failure

The hantavirus is known to cause hemorraghic fever with renal syndrome (HFRS), which is widely spread in Europe and Asia. Several reports have shown an association of hantavirus antibody titers and the occurrence of renal dysfunction. From these observations, it appears that the virus is widely distributed, and different strains prevail in various areas. In the present work we studied 81 patients with end-stage renal-failure under hemodialysis (HD) treatment, 55 with mild to moderate renal failure, and 50 healthy subjects for the presence of antibodies to Hantaan and Puumala viruses. We found that 12.3% of the hemodialysis patients and 9% of the mild to moderate renal failure patients had elevated IgG anti-body titers to Puumala virus compared with 2% of the controls. IgM antibodies to Puumala virus was principally elevated in patient with chronic renal failure (CRF) not on hemodialysis (14.5%) compared with the hemodialyzed (1.2%) and controls (0%) subjects. Hantaan virus IgG antibodies were detected in 3.7% of the HD patients, 5.5% of the CRF not on HD, and in none of the controls. IgM Hantaan antibodies were found only in the non-HD renal failure patients. None of the sera were found to contain antibodies to phospholipids or single-stranded DNA. These results emphasize the widespread nature of infection with hantaviruses and imply that elaborate testing for these serologies should be performed, especially in patients with unexplained renal failure.

Nucleotide sequence and phylogenetic analysis of the medium (M) genomic RNA segments of three hantaviruses isolated in China

The medium (M) genome segment of hantaviruses (family Bunyaviridae) encodes the two virion glycoproteins. G1 and G2, as a precursor protein in the complementary sense RNA. We determined the nucleotide sequences of the M genome segments of three Chinese hantavirus isolates, a Hantaan-type (HTN) virus designated A9 and two Seoul-type (SEO) viruses designated L99 and HB55, and compared them to those of other HTN or SEO viruses isolated in Eastern Asia. The M segment of A9 is 3616 nucleotides in length and shows 99.5% identity at the nucleotide level and 99.1% identity at the amino acid level to that of the Chinese HTN isolate HV114. The M segments of L99 and HB55 are 3652 nucleotides in length, one nucleotide longer than the M segments of other sequenced SEO isolates such as SEO 80-39, SR-11, and Biken-1. The Chinese SEO isolates showed 95% nucleotide sequence identity and 99% amino acid sequence identity to SEO 80-39. We also sequenced a 736 nucleotides region of the M genome segment of another Chinese SEO isolate, R22, which revealed errors in the published data. Phylogenetic analysis of the available sequences indicated that both the Chinese HTN- and SEO-type viruses form lineages distinct from those of the isolates from other parts of Eastern Asia.

Protection against hantavirus infection by dam's immunity transferred vertically to neonates

Antibodies to hantavirus, Seoul type B-1 strain, vertically transferred to rat neonates prevented lethal as well as persistent infection. When relatively high titer viruses were inoculated into neonates, the mother's antibodies protected all the neonates from lethal virus infection. However, the antibodies could not protect all of the neonates from persistent infection but only half of them underwent persistent infection. The other half was completely cured but also became persistently infected when rechallenged with the active viruses after reaching maturity.

Serological evidence of Hantavirus disease in Northern Ireland

Since, to our knowledge, no clinically documented cases of haemorrhagic fever with renal syndrome (HFRS) have been reported in Northern Ireland, a sero-epidemiological study was carried out to assess the degree of Hantavirus immunity in a group of 627 Northern Irish patients presenting with symptoms suggestive of HFRS and 100 healthy controls. IFA screening for IgG Hantavirus specific antibodies was carried out with a panel of up to 9 different Hantaviral antigens. IgM screening was performed using a commercially available mu-capture ELISA based upon two recombinant Hantaviral nucleocapsid antigens. A seropositivity of 2.1% (15/727) was recorded, with an almost exclusive reaction against a rat-derived R22VP30 strain of the Seoul serotype. Sole reliance upon non-rat-derived classic screening antigens Hantaan (HTN 76-118) and Puumala (CG 18-20) would have resulted in the detection of only 2/15 (13.3%) of cases in IgG IFA, and 8/14 (57.1%) of the cases in IgG ELISA. The findings indicate that for the first time in Europe, and more specifically in N. Ireland, non-laboratory outbreaks of HFRS may be caused by wild rats acting as a reservoir for a Seoul-like Hantavirus. Conventional Hantavirus serology using Hantaan and Puumala as screening antigens does not appear sufficient for the detection of such cases of HFRS. Hence, we propose the addition of a rat derived Hantaviral antigen to the antigen screening panel as a means of improving the specificity of the detection methods.

Renal lesions in rats infected with Rattus serotype hantavirus (SR-11 strain)

Hemorrhagic fever with renal syndrome (HFRS) virus, strain SR-11 (SR) was inoculated intraperitoneally into specific-pathogen-free (SPF) newborn rats, from which the kidney lesions were examined pathologically. The infected rats revealed proteinuria on and after 16 days postinoculation (PI). Histologically, the epithelial cells of the renal tubules showed mild vacuolar and granular degeneration with cytoplasmic inclusion bodies (CIB) on and after 16 days PI. Ultrastructurally, a decrease in number of mitochondria and endocytic vesicles was recognized in the epithelial cells of the proximal renal tubules. Occasionally, both the proximal and distal renal tubular cells had CIB near well-developed Golgi apparatus on and after 13 days PI. Immunohistochemically, CIB were positive for anti-SR nucleocapsid antibody, but negative for anti-SR envelope protein antibody. From the results obtained here, it was concluded that the proteinuria in rats infected with HFRS virus resulted from an insufficiency of reabsorption in the proximal renal tubules, and that CIB consisted of the viral nucleocapsid protein.

Characteristics of passive immunity against hantavirus infection in rats

The protective effects of passively administered antibodies against hantavirus infection were studied in newborn rats. Death as well as infection were completely prevented from intraperitoneal challenge of strain SR-11 (SR) (2 x 10(3) FFU, 10(2.1) LD50), in newborn rats which received 0.1 ml of anti-SR rat serum (neutralizing antibody titer, 1:640) 4 hr before the virus challenge. In these rats, no virus was detected in the peritoneal macrophages, lung, kidney, and brain. The immune serum infusion before the virus challenge also conferred protection to rats against an intramuscular or subcutaneous challenge of strain SR, but did not protect the rats against intracerebral challenge of the virus. In the rats which received the immune serum after the challenge, infection was not prevented, although some of the animals were protected from the death. Virus titers in the lung, kidney, and brain of the rats were reduced by the transfer of the immune serum even as late as 72 hr after the challenge. Cross-protection in the rats which received the immune serum was strong between strains SR and KI-262 within the same serotype, but very weak between strains SR and Hantaan 76-118 of different serotypes.

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.

Role of maternal antibody in protection from hemorrhagic fever with renal syndrome virus infection in rats

The effect of maternal antibody on the protection of newborn rats from infection of HFRS virus strain SR-11 was examined. Antibody to HFRS virus was transferred from immune dams to their offspring prenatally as well as postnatally. IgG antibody was detected in the sera of fetuses by IFA test (titers from 1:64 to 1:256) and in fetal fluids (1:32) obtained from the uteri of immune dams at 20 days after mating. In the sera of the newborn, IgG titers of maternal antibody ranged from 1:64 to 1:256 just after birth, reached a peak titer around 1:2,048 at 2 weeks after birth, then declined and disappeared at about 8 weeks of age. No IgA and IgM antibodies were detected in the sera of fetuses and newborns. After intraperitoneal challenge by strain SR-11 (10(2.2) LD50), death and infection of 2-day-old rats from immune dams were prevented by the presence of maternal antibody. The protective effect of maternal antibody remained in 8-week-old rats having an IFA titer of maternal antibody as low as 1:16, and even in some 10-week-old rats with negative tests for maternal antibody.

Development of inactivated vaccine against virus causing haemorrhagic fever with renal syndrome

B-1 virus belonging to the hantavirus group was serially passaged in the brains of newborn mice. Inactivated vaccine was prepared from the brains after inactivation with formalin and then purification by ultracentrifugation. The antigenic potency of this vaccine in vitro was determined by antibody-bound enzyme-linked immunosorbent assay (ELISA) and serial diluted vaccine bound to an aluminium hydroxide gel was inoculated into Balb/c mice to test immunogenicity. After two injections of this vaccine preparation, antibodies were detected in the mice by immunofluorescent, neutralizing and haemagglutination inhibition antibody tests. When mice immunized with this vaccine were challenged with B-1 virus and Hantaan virus (KHF-83-61BL strain), the virus titres in their lungs and spleens were significantly less than those in non-immunized mice. These results suggest that inactivated B-1 virus vaccine is effective against virus challenge by homotypic (B-1 virus) and heterotypic (Hantaan virus) viruses.

Hemorrhagic fever with renal syndrome in Yugoslavia: detection of hantaviral antigen and antibody in wild rodents and serological diagnosis of human disease

Lung tissues from 547 rodents and 26 insectivores captured between 1981 and 1984 in central Bosnia (Fojnica) and central Serbia (Cacak), 2 regions known to be endemic for hemorrhagic fever with renal syndrome (HFRS), were examined for hantaviral antigen by the indirect immunofluorescent antibody technique. Antigen was detected in 17/231 Apodemus flavicollis, 3/187 A. sylvaticus, 1/46 A. agrarius, 4/32 Mus musculus, and 3/28 Clethrionomys glareolus. In addition, antibodies against Hantaan and Puumala viruses were found in serum pooled from 2 C. glareolus captured in Fojnica and 6 Pitimys subterraneus caught in Cacak. Sera of 27 HFRS patients from different parts of Yugoslavia were tested against 3 serotypes of hantavirus. Patients from Bosnia and Serbia had highest titers against Hantaan virus, while patients from Croatia had highest titers against Puumula virus, the agent of nephropathia epidemica.

Serological survey of Prospect Hill virus infection in indigenous wild rodents in the USA

We found serological evidence of infection with Prospect Hill virus, a Hantaan-like virus isolated from meadow voles (Microtus pennsylvanicus), in microtine and cricetid rodents trapped in Maryland, West Virginia, Minnesota and California, USA. Fluorescent antibodies were detected in sera from M. pennsylvanicus (74/277), M. californicus (39/185), Clethrionomys gapperi (5/51), Peromyscus maniculatus (4/22) and P. truei (1/11). Sera from seropositive P. maniculatus contained neutralizing antibodies against Prospect Hill virus, confirming that infection with Prospect Hill virus or antigenically related viruses is not restricted to microtine rodents in the USA. Despite the widespread distribution of Prospect Hill virus in indigenous rodents, the recent demonstration that American mammalogists are only rarely infected supports the view that the overall risk of Prospect Hill virus infection in man is low.

Serological evidence of Hantaan-related viruses in Hong Kong

Sera from rats (Rattus norvegicus), domestic animals and man in Hong Kong were studied by immunofluorescent antibody assay and plaque reduction neutralization tests for evidence of infection by Hantaan-related viruses. Antibody probably arising from infection by Seoul or a Seoul-like virus was detected in rat and human sera (and one pig serum), highlighting the potential public health importance of this group of viruses in Hong Kong, and in the region.

Epidemiological studies of hemorrhagic fever with renal syndrome (HFRS) related virus infection among urban rats in Hokkaido, Japan

Seroepidemiological studies of hemorrhagic fever with renal syndrome (HFRS) virus infection were carried out among urban rats (Rattus norvegicus and Rattus rattus) and small field rodents in Hokkaido, Japan. An urban rat colony that was seropositive to SR-11 strain of HFRS virus (laboratory rat origin) was demonstrated in February 1983 at a dumping ground area of Kami-iso Town near Hakodate port. An HFRS-related virus, named KI-262 strain, was isolated from the lung tissue of a seropositive rat using Vero-E6 cell culture. Antigenicity of the isolate was closely related to Hantaan 76-118 and SR-11 strains by the indirect immunofluorescent antibody (IFA) test. No seropositive rat was found among the 861 rats captured in 38 other regions. It is unclear whether or not the infected rats in the positive area were introduced from abroad, though the area is located near Hakodate International Port. Furthermore, higher positive rates of urban rats in the Kami-iso area were observed in the spring and winter than in the summer and fall. Significantly high proportion of positive cases was observed among adult rats (six months or older) than among younger animals. The seasonal and age distribution of positive cases suggested that the virus was not readily transmitted from one infected rat to another. One seropositive case of a small field mouse (Clethrionomys rufocanus bedfordiae) was detected around the Kami-iso area.

Characterization of glycoproteins of viruses causing hemorrhagic fever with renal syndrome (HFRS) using monoclonal antibodies

Viruses causing hemorrhagic fever with renal syndrome (HFRS) encode two glycoproteins, G1 and G2. For determination of the biological functions of these glycoproteins, we isolated 15 hybridomas secreting monoclonal antibodies directed against the glycoproteins of the B-1 and Hantaan viruses (HV). From results of neutralizing and hemagglutination inhibition (HI) tests, and studies on the antigenic reactivities of the antibodies with other HV-related viruses by immunofluorescence, we classified these hybridoma clones into two groups producing antibodies to the G1 proteins of the B-1 virus, six groups producing antibodies to G2 proteins of the B-1 virus, and four groups producing antibodies to the G2 protein of HV. Of the antibodies to G2 produced by 12 clones, groups A and B had high HI activity with HV-related virus cross-reactivity and moderate neutralizing activity, group C had moderate HI activity with virus specificity but low neutralizing activity, group G had high neutralizing activity and low HI activity, and five other groups had little or no HI or neutralizing activity. Group A reacting with G1 protein had low level of both neutralizing and HI activity, while group B had no HI activity. One clone of monoclonal antibody had high neutralizing activity and no HI activity, but it did not react with either polypeptide by immunoprecipitation followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis or by the immunoblotting method. These data suggest that both glycoproteins are the targets of neutralizing antibodies. Furthermore, the results indicate that the antigenic determinants with hemagglutination activity are mainly on the G2 protein, and that the domains related to neutralizing activity and to HI activity are separate.

Pathogenesis of experimental Hantaan virus infection in laboratory rats

Weanling Fischer rats inoculated intramuscularly with Hantaan virus (strain 76-118) developed subclinical infections characterized by transient viremia and shedding of virus in saliva, persistence of virus in lung, pancreas, spleen and liver, and development of fluorescent and neutralizing antibodies in serum with immune complex deposition in lung. Viremia and virus shedding in saliva occurred 10 to 13 days after inoculation. Horizontal intracage transmission of infection occurred between 35 and 63 days post-inoculation, long after disappearance of virus in oropharyngeal secretions and blood. Multiple attempts to demonstrate infectious virus in feces and urine during this period were unsuccessful. The inability to detect virus in urine samples of experimentally infected rats may have resulted from intermittent or low-titered viruria. This contrasts sharply with the prolonged high-titered viruria reported in striped field mice (Apodemus agrarius) infected with Hantaan virus, suggesting differences in the mode(s) of virus transmission in nature.

Antiviral neutralizing antibody to Hantaan virus as determined by plaque reduction technique

The 76--118 strain of Hantaan virus was titrated in E6 (Vero) cells by the plaque method using agarose overlay medium. Visible plaques, formed 10 days post-infection, were uniformly 2--3 mm in diameter. Dose-response experiments showed that a single infectious particle initiated the formation of a plaque. Infectivity titers by the plaque method were equivalent to those obtained by the endpoint method (TCID50) using the immunofluorescence antibody technique (IFA) for antigen detection. The single-cycle growth pattern of the virus showed an eclipse phase of 7 to 9 hours, with production of cell-free infectious virus 18 hours post-infection. Plaque reduction neutralization tests suggested that complement enhanced the neutralizing activity of sera; rat sera were particularly complement-dependent. The plaque reduction neutralization test was about 10 times more sensitive than the TCID50 neutralization test. Convalescent phase sera from patients with hemorrhagic fever with renal syndrome (HFRS) having higher IF antibody titers to Hantaan virus than to nephropathia epidemica (NE) virus were capable of neutralizing Hantaan virus, while sera from patients with higher IF antibody titers to NE virus than Hantaan virus did not contain neutralizing antibody to Hantaan virus.

Evaluation of focus reduction neutralization test with peroxidase-antiperoxidase staining technique for hemorrhagic fever with renal syndrome virus

Titers of hemorrhagic fever with renal syndrome virus were estimated by counting foci stained with peroxidase-antiperoxidase or by using immunofluorescence methods. Foci stained with PAP were clearer and easier to count. The peroxidase-antiperoxidase method showed a linear relationship between virus concentration and the number of foci. A focus-reduction neutralizing antibody test was performed with immune rat sera and sera from patients. Again, the peroxidase-antiperoxidase method proved to be more convenient and reliable than the immunofluorescence method. Antigenic differences between Hantaan virus, 76-118 and hemorrhagic fever with renal syndrome virus B-1 were clearly demonstrated by the neutralizing antibody test.

Experimental infection in newborn mice and rats by hemorrhagic fever with renal syndrome (HFRS) virus

Newborn mice and rats were inoculated intracerebrally (ic) or intraperitoneally (ip) with Hantaan virus (76-118 strain) or HFRS-related virus (B-1 strain). The mortality and the influence on the increase of body weight in newborn mice were higher in the groups infected with the 76-118 strain than in the groups infected with the B-1 strain, while the B-1 strain was more virulent in rats than the 76-118 strain. Virus isolation from rats inoculated with either strain was attempted 7 and 11 weeks after inoculation. Virus could be isolated from various organs of rats infected with the B-1 strain, while it was recovered from only the brain and lungs of rats infected with the 76-118 strain. Viral antigen was readily detected in various organs of rats infected with the B-1 strain, but the amount and distribution of antigens were less in rats infected with the 76-118 strain. Our results suggest that the virulence of HFRS-related virus is variable, depending on the species of infected animals as well as on the virus strains. The virus also persists in the injected animals with high titers of antibodies for at least 11 weeks.

Antigenic differences between two viruses, isolated in Japan and Korea, that cause hemorrhagic fever with renal syndrome

Hantaan virus (HV) 76-118, isolated from Apodemus agrarius coreae in Korea, and hemorrhagic fever with renal syndrome (HFRS) virus B-1, isolated from a rat in Japan, were examined for polypeptide compositions and for differences in immune responses in rats. In immunoprecipitation experiments, a major polypeptide of ca. 50 kilodaltons (K) was detected with antisera against HV 76-118 in cell extracts from Vero E6 cells infected with HFRS virus B-1, whereas three major polypeptides of 74 K (glycosylated), 57 K (glycosylated), and 50 K were detected with antisera against HFRS virus B-1. On the other hand, two polypeptides with molecular weights of 55,000 (glycosylated) and 50,000 were detected with either antiserum in cell extracts infected with HV 76-118. In neutralizing antibody tests with antisera prepared in rats, a remarkable difference in antibody titer (5 to 30 times higher to the homologous virus than to the heterologous virus) was observed between the two viruses. However, this difference was not so marked (1 to 4 times higher to the homologous virus) in the immunofluorescent antibody test. Twenty hybrid cell lines producing mouse monoclonal antibodies against HV 76-118 were isolated by fusion of spleen cells from BALB/c mice immunized against HV (strain 76-118) with mouse myeloma cells. The specificity of these monoclonal antibodies was established by immunofluorescent antibody, neutralizing antibody, and fluorescent antibody to membrane antigen tests and by analysis with sodium dodecyl sulfate-polyacrylamide gel electrophoresis. These hybrid cell lines were classified into three groups based principally on the IF staining pattern of the HV-infected cells: (i) antibodies which showed a discrete patch pattern in the cytoplasm by the immunofluorescent antibody test, reacting with the membrane antigen of infected cells and immunoprecipitating a 55-K glycoprotein from HV 76-118-infected cell lysates and a 57-K glycoprotein from the heterologous (strain B-1) HFRS virus-infected cell lysates. Among these, depending on the neutralizing antibody activity and the reaction with the heterologous antigen, three subgroups designated I-A, I-B, and I-C were established; (ii) antibodies which showed large granular dots in the cytoplasm, neither having neutralizing antibody activity nor immunoprecipitating any antigen; (iii) antibodies which showed defined granular dots throughout the cytoplasm, reacting with a 50-K polypeptide of both virus strains. These antibodies also classified into two subgroups based on the reactivity with the B-1 strain.(ABSTRACT TRUNCATED AT 400 WORDS)

Laboratory rat associated outbreak of haemorrhagic fever with renal syndrome due to Hantaan-like virus in Belgium

Hantaan-like virus was identified as the cause of three cases of acute renal failure in staff handling laboratory rats on a Belgian university campus. Serological studies revealed infected rat strains at different sites on the campus and evidence of past and recent infections in 39 staff members and of infection in 50% of exposed staff. Hantaan-reactive antibody was very rare in control populations. Staff or rats at three other Belgian institutions had no signs of infection. The origin of the virus was not identified. Infected rats have been removed. These are the first confirmed cases, outside East Asia, of human illness due to rat-borne Hantaan-like virus, and of infection in laboratory rats. Surveillance of rat colonies is also recommended in countries which, like Belgium, have no previously recognised cases of haemorrhagic fever with renal syndrome.