Detection of hantaviral antibodies among patients with hepatitis of unknown etiology in Japan

Hantavirus infection in type I interferon receptor-deficient (A129) mice

Type I interferon receptor knockout mice (strain A129) were assessed as a disease model of hantavirus infection. A range of infection routes (intramuscular, intraperitoneal and intranasal) were assessed using minimally passaged Seoul virus (strain Humber). Dissemination of virus to the spleen, kidney and lung was observed at 5 days after intramuscular and intraperitoneal challenge, which was resolved by day 14. In contrast, intranasal challenge of A129 mice demonstrated virus tropism to the lung, which was maintained to day 14 post-challenge. These data support the use of the A129 mouse model for future infection studies and the in vivo evaluation of interventions.

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.

Detection and genetic characterization of Seoul virus from commensal brown rats in France

Background

Hantaviruses are single-stranded RNA viruses, which are transmitted to humans primarily via inhalation of aerosolised virus in contaminated rodent urine and faeces. Whilst infected reservoir hosts are asymptomatic, human infections can lead to two clinical manifestations, haemorrhagic fever with renal syndrome (HFRS) and hantavirus cardiopulmonary syndrome (HCPS), with varying degrees of clinical severity. The incidence of rodent and human cases of Seoul virus (SEOV) in Europe has been considered to be low, and speculated to be driven by the sporadic introduction of infected brown rats (Rattus norvegicus) via ports.

Methods

Between October 2010 and March 2012, 128 brown rats were caught at sites across the Lyon region in France.

Results

SEOV RNA was detected in the lungs of 14% (95% CI 8.01 – 20.11) of brown rats tested using a nested pan-hantavirus RT-PCR (polymerase gene). Phylogenetic analysis supports the inclusion of the Lyon SEOV within Lineage 7 with SEOV strains originating from SE Asia and the previously reported French & Belgian SEOV strains. Sequence data obtained from the recent human SEOV case (Replonges) was most similar to that obtained from one brown rat trapped in a public park in Lyon city centre. We obtained significantly improved recovery of virus genome sequence directly from SEOV infected lung material using a simple viral enrichment approach and NGS technology.

Conclusions

The detection of SEOV in two wild caught brown rats in the UK and the multiple detection of SEOV infected brown rats in the Lyon region of France, suggests that SEOV is circulating in European brown rats. Under-reporting and difficulties in identifying the hantaviruses associated with HFRS may mask the public health impact of SEOV in Europe.

An efficient in vivo method for the isolation of Puumala virus in Syrian hamsters and the characterization of the isolates from Russia

Puumala virus (PUUV) and other Arvicolinae-borne hantaviruses are difficult to cultivate in cell culture. To isolate these hantaviruses efficiently, hantavirus nucleocapsid protein (NP)-positive but seronegative wild rodents were selected by NP-detection ELISA. Three of 68 Myodes glareolus captured in Samara, Russia, were NP-positive and seronegative. Syrian hamsters were inoculated with lung homogenates from NP-positive rodents for virus propagation. Virus isolation in vitro was carried out by inoculation of lung homogenates of NP-positive hamsters to Vero E6 cell monolayers. Two PUUV strains (Samara49/CG/2005 and Samara94/CG/2005) from M. glareolus were isolated in Vero E6 cells. Nucleotide and amino acid sequence identities of the S segment of these isolates to those of PUUV F-s808 from a fatal HFRS patient in Samara region were 96.7-99.3% and 99.3-100.0%, respectively. Morphologic features of Vero E6 cells infected with PUUV strain Samara49/CG/2005 were quite similar to those of Hantaan virus-infected cells. Isolation of Hokkaido virus from Myodes rufocanus captured in Hokkaido, Japan, was also performed. Hokkaido virus NP and RNA were recovered and maintained in hamsters. These results suggest that inoculation of Syrian hamsters with rodent samples is an efficient method for the isolation and maintenance of PUUV and other Arvicolinae-borne hantaviruses.

Serological and genetic evidence for the presence of Seoul hantavirus in Rattus norvegicus in Flanders, Belgium

Seoul hantavirus (SEOV), carried by Rattus rattus (black rat) and R. norvegicus (Norway, brown rat), was reported to circulate as well as cause HFRS cases in Asia. As Rattus sp. are present worldwide, SEOV has the potential to cause human disease worldwide. In Europe however, only SEOV prevalence in rats from France was reported and no confirmed cases of SEOV infection were published. We here report genetic and serological evidence for the presence of SEOV virus in brown rat populations in Belgium. We also serologically screened an at-risk group that was in contact with R. norvegicus on a daily basis and found no evidence for SEOV infection.

Genetic analysis of hantaviruses carried by Myodes and Microtus rodents in Buryatia

Hantavirus genome sequences were recovered from tissue samples of Myodes rufocanus, Microtus fortis and Microtus oeconomus captured in the Baikal area of Buryatia, Russian Federation. Genetic analysis of S- and M-segment sequences of Buryatian hantavirus strains showed that Myodes-associated strains belong to Hokkaido virus (HOKV) type while Microtus-associated strains belong to Vladivostok virus (VLAV) type. On phylogenetic trees Buryatian HOKV strains were clustered together with M. rufocanus- originated strains from Japan, China and Far-East Russia (Primorsky region). Buryatian Microtus- originated strains shared a common recent ancestor with M. fortis- originated VLAV strain from Far-East Russia (Vladivostok area). Our data (i) confirm that M. rufocanus carries a hantavirus which is similar to but distinct from both Puumala virus carried by M. glareolus and Muju virus associated with M. regulus, (ii) confirm that M. fortis is the natural host for VLAV, and (iii) suggest M. oeconomus as an alternative host for VLAV.

Hantavirus infection in East Asia

Hantaviruses are enveloped RNA viruses that belong to the Hantavirus genus of the family Bunyaviridae. These viruses persistently infect their rodent reservoirs without causing disease. The virus is transmitted to humans via the inhalation of infectious aerosols generated from contaminated animal secretions or through the contaminated saliva of animal bites. Hantaviruses cause haemorrhagic fever with renal syndrome in Euro-Asia, and hantavirus pulmonary syndrome (HPS) in North and South America. Here, we review the epidemiology and epizootiology of hantavirus infection in Asian countries.

Nucleocapsid protein of cell culture-adapted Seoul virus strain 80-39: analysis of its encoding sequence, expression in yeast and immuno-reactivity

Seoul virus (SEOV) is a hantavirus causing a mild to moderate form of hemorrhagic fever with renal syndrome that is distributed mainly in Asia. The nucleocapsid (N) protein-encoding sequence of SEOV (strain 80-39) was RT-PCR-amplified and cloned into a yeast expression vector containing a galactose-inducible promoter. A survey of the pattern of synonymous codon preferences for a total of 22 N protein-encoding hantavirus genes including 13 of SEOV strains revealed that there is minor variation in codon usage by the same gene in different viral genomes. Introduction of the expression plasmid into yeast Saccharomyces cerevisiae resulted in the high-level expression of a hexahistidine-tagged N protein derivative. The nickel-chelation chromatography purified, yeast-expressed SEOV N protein reacted in the immunoblot with a SEOV-specific monoclonal antibody and certain HTNV- and PUUV-cross-reactive monoclonal antibodies. The immunization of a rabbit with the recombinant N protein resulted in the induction of a high-titered antibody response. In ELISA studies, the N protein was able to detect antibodies in sera of experimentally infected laboratory rats and in human anti-hantavirus-positive sera or serum pools of patients from different geographical origin. The yeast-expressed SEOV N protein represents a promising antigen for development of diagnostic tools in serology, sero prevalence studies and vaccine development.

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.

Development of an efficient method for recovery of Puumala and Puumala-related viruses by inoculation of Mongolian gerbils

Puumala (PUU) virus and PUU-related viruses are difficult to isolate in cell culture. To determine whether animal inoculation would be a better alternative for virus recovery, the Sotkamo strain of PUU virus was inoculated into several animal species. Newborn Mongolian gerbils (MGs), mice, and rats were infected with the Sotkamo strain by intracerebral (ic), intraperitoneal (ip), and subcutaneous (sc) inoculation. Antibodies to PUU appeared in MGs at 30 days post-infection (dpi), and in mice and rats at 15 dpi. Interestingly, virus appeared at 7 dpi in lung and brain of MGs inoculated via ic and ip routes. Virus was detected in all tested tissues of MGs at 15 dpi, with a peak level of 1.36 x 10 (5) focus forming units (FFU)/g in brain tissue. The virus titer declined with the onset of the antibody response and became undetectable by 75 dpi, when the antibody titer reached the maximum level. The appearance of the virus in mice and rats was delayed as compared to MGs, and the virus titer was apparently lower, at approximately 4 to 8 x 10(3) FFU/g, at 15 dpi. In addition, lung homogenates of antibody-positive Clethrionomys (C.) rufocanus (captured in Tobetsu, Hokkaido, Japan) were inoculated into MGs by the ic route. PUU-related viral RNA was detected at 16 dpi in the brains of MG inoculated with the lung homogenate, and antibodies were detected at 45 dpi. These findings indicate that newborn MG inoculation is an efficient method to recover PUU and PUU-related viruses.

Characteristics of Puumala and Dobrava infections in Croatia

In this study, two different hantaviruses, Puumala virus (PUUV) and Dobrava virus (DOBV), were demonstrated for the first time to coexist and cause hemorrhagic fever with renal syndrome (HFRS) in Croatia. Phylogenetic analysis showed some differences among the nucleotide sequences of PUUV originating from Dinara mountain, which was more closely related to Austrian PUUV than other Croatian PUUV from Mala Kapela mountain. More consistency was found among the Croatian DOBV. HFRS was verified in 85 of 201 suspected cases recorded in 1995 during the largest HFRS outbreak in Croatia. Most of these cases were soldiers. With the exception of the coastal region and islands, all of Croatia was found to be an area endemic for HFRS. A statistically significantly higher proportion of DOBV-infected patients had acute renal failure, visual disturbance, severe thrombocytopenia, and elevated levels of nonsegmented leukocytes, creatine, and total bilirubin. The prevalence of gastrointestinal and electrocardiography disorders also was greater in DOBV-infected patients. Interestingly, significantly more PUUV-infected patients had elevated systolic blood pressure on admission to the hospital. Further prospective studies are necessary to shed more light on differences in HFRS severity associated with PUU and DOB viruses.

Molecular evolution of Puumala hantavirus

Puumala virus (PUUV) is a negative-stranded RNA virus in the genus Hantavirus, family Bunyaviridae. In this study, detailed phylogenetic analysis was performed on 42 complete S segment sequences of PUUV originated from several European countries, Russia, and Japan, the largest set available thus far for hantaviruses. The results show that PUUV sequences form seven distinct and well-supported genetic lineages; within these lineages, geographical clustering of genetic variants is observed. The overall phylogeny of PUUV is star-like, suggesting an early split of genetic lineages. The individual PUUV lineages appear to be independent, with the only exception to this being the Finnish and the Russian lineages that are closely connected to each other. Two strains of PUUV-like virus from Japan form the most ancestral lineage diverging from PUUV. Recombination points within the S segment were searched for and evidence for intralineage recombination events was seen in the Finnish, Russian, Danish, and Belgian lineages of PUUV. Molecular clock analysis showed that PUUV is a stable virus, evolving slowly at a rate of 0.7 x 10(-7) to 2.2 x 10(-6) nt substitutions per site per year.