Ribavirin therapy for Hantaan virus infection in suckling mice

Screening and Identification of HTNVpv Entry Inhibitors with High-throughput Pseudovirus-based Chemiluminescence

Hantaviruses, such as Hantaan virus (HTNV) and Seoul virus, are the causative agents of Hantavirus cardiopulmonary syndrome (HCPS) and hemorrhagic fever with renal syndrome (HFRS), and are important zoonotic pathogens. China has the highest incidence of HFRS, which is mainly caused by HTNV and Seoul virus. No approved antiviral drugs are available for these hantaviral diseases. Here, a chemiluminescence-based high-throughput-screening (HTS) assay was developed and used to screen HTNV pseudovirus (HTNV_pv) inhibitors in a library of 1813 approved drugs and 556 small-molecule compounds from traditional Chinese medicine sources. We identified six compounds with in vitro anti-HTNV_pv activities in the low-micromolar range (EC₅₀ values of 0.1–2.2 ​μmol/L; selectivity index of 40–900). Among the six selected compounds, cepharanthine not only showed good anti-HTNV_pv activity in vitro but also inhibited HTNV_pv-fluc infection in Balb/c mice 5 ​h after infection by 94% (180 ​mg/kg/d, P ​< ​0.01), 93% (90 ​mg/kg/d, P ​< ​0.01), or 92% (45 ​mg/kg/d, P ​< ​0.01), respectively, in a bioluminescent imaging mouse model. A time-of-addition analysis suggested that the antiviral mechanism of cepharanthine involves the membrane fusion and entry phases. Overall, we have established a HTS method for antiviral drugs screening, and shown that cepharanthine is a candidate for HCPS and HFRS therapy. These findings may offer a starting point for the treatment of patients infected with hantaviruses.

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A chemiluminescence-based high-throughput-screening (HTS) assay was used to screen HTNV pseudovirus (HTNV_pv) inhibitors.

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Cepharanthine showed good anti-HTNV_pv activity in vitro and in vivo.

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A time-of-addition analysis suggested that cepharanthine involves the membrane fusion and entry phases.

Global Comprehensive Outlook of Hantavirus Contagion on Humans: A Review

Hantaviruses are rodent viruses that have been identified as etiologic agents of 2 diseases of humans: hemorrhagic fever with renal syndrome (HFRS) and nephropathiaepidemica (NE) in the Old World and Hantavirus pulmonary syndrome (HPS) in the New World. Orthohantavirus is a genus of sin- gle-stranded, enveloped, negative-sense RNA viruses in the family Hantaviridae of the order Bunyavi- rales. The important reservoir of Hantaviruses is rodents. Each virus serotype has its unique rodent host species and is transmitted to human beings with the aid of aerosolized virus, which is shed in urine, fae- ces and saliva and hardly by a bite of the contaminated host. Andes virus is the only Hantavirus identified to be transmitted from human-to-human and its major signs and symptoms include fever, headache, mus- cle aches, lungs filled with fluid etc. In the early 1993, this viral syndrome appeared in the Four Cor- ner location in the south western United States. The only accepted therapeutics for this virus is Ribavirin. Recently, serological examinations to identify Hantavirus antibodies have become most popular for in- vestigation among humans and rodent reservoirs.

OUP accepted manuscript

Hantavirus-induced diseases are emerging zoonoses with endemic appearances and frequent outbreaks in different parts of the world. In humans, hantaviral pathology is characterized by the disruption of the endothelial cell barrier followed by increased capillary permeability, thrombocytopenia due to platelet activation/depletion and an overactive immune response. Genetic vulnerability due to certain human leukocyte antigen haplotypes is associated with disease severity. Typically, two different hantavirus-caused clinical syndromes have been reported: hemorrhagic fever with renal syndrome (HFRS) and hantavirus cardiopulmonary syndrome (HCPS). The primarily affected vascular beds differ in these two entities: renal medullary capillaries in HFRS caused by Old World hantaviruses and pulmonary capillaries in HCPS caused by New World hantaviruses. Disease severity in HFRS ranges from mild, e.g. Puumala virus-associated nephropathia epidemica, to moderate, e.g. Hantaan or Dobrava virus infections. HCPS leads to a severe acute respiratory distress syndrome with high mortality rates. Due to novel insights into organ tropism, hantavirus-associated pathophysiology and overlapping clinical features, HFRS and HCPS are believed to be interconnected syndromes frequently involving the kidneys. As there are no specific antiviral treatments or vaccines approved in Europe or the USA, only preventive measures and public awareness may minimize the risk of hantavirus infection. Treatment remains primarily supportive and, depending on disease severity, more invasive measures (e.g., renal replacement therapy, mechanical ventilation and extracorporeal membrane oxygenation) are needed.

Hantavirus Infections-Treatment and Prevention

Purpose of review

Hantavirus infection is an emerging zoonosis and there are two main clinical presentations, hemorrhagic fever with renal syndrome (HFRS) and Hantavirus pulmonary syndrome (HPS). Although Hantavirus infections have a worldwide distribution with a high mortality rate, a safe and effective vaccine or an antiviral drug against the Hantavirus disease is yet to be available. This review summarizes all the efforts undertaken to develop medical countermeasures in vitro, in vivo, and human clinical trials against Hantavirus infections.

Recent findings

Multiple antivirals are shown to be effective with limited evidence and recent studies on immunotherapy were not very conclusive. There are multiple vaccine candidates with evidence of conferring long protective immunity against Hantaviruses. Some of these had been already trialed on humans.

Summary

At present, severe HPS or HFRS case management is purely based on supportive treatments, often in an intensive care unit. Rodent control and public health education and promotion play a major role in preventing Hantavirus infection.

Development of small-molecule inhibitors against hantaviruses

Hantavirus (HV), a pathogen of animal infectious diseases that poses a threat to humans, has attracted extensive attention. Clinically, HV can cause hemorrhagic fever with renal syndrome (HFRS) and hantavirus pulmonary syndrome (HPS), between which HFRS is mostly in Eurasia, and HPS is mostly in the Americas. This paper reviews the research progress of small-molecule inhibitors of HV.

Antiviral Therapy of Haemorrhagic Fevers and Arbovirus Infections

RNA viruses of the families Arena-, Bunya-, Filo-, Flavi-and Togaviridae cause illness in humans ranging from mild, non-specific febrile syndromes to fulminant, lethal haemorrhagic fever. They are transmitted from animals to humans and from human to human by arthropods, aerosols or contact with body fluids. Antiviral compounds, convalescent plasma and interferon inhibit many of these agents in vitro and in virus-infected animals. Drug or plasma treatment is now in use for several human diseases, and would probably be beneficial for a number of others for which there is only limited treatment experience. Success is linked to early diagnosis and initiation of therapy. Ribavirin is used to treat Lassa fever and haemorrhagic fever with renal syndrome, and would probably be effective for Crimean-Congo haemorrhagic fever and for all New World arenavirus diseases. The value of ribavirin in the early treatment of hantavirus pulmonary syndrome is under evaluation. Convalescent plasma is the therapy of choice for Argentine haemorrhagic fever, and would also probably be effective for other New World arenaviruses and some other infections if a safe supply of plasma could be maintained. Ribavirin and interferon-α have both shown protective efficacy in non-human primates infected with Rift Valley fever virus. No effective therapy has yet been identified for filovirus infections, but results in animal models are encouraging. More clinical research is urgently needed. Even if placebo-controlled drug trials cannot be performed, conscientious reports of the results of therapy in limited numbers of patients can still provide evidence of antiviral drug effects.

Vaccines and Therapeutics Against Hantaviruses

Hantaviruses (HVs) are rodent-transmitted viruses that can cause hantavirus cardiopulmonary syndrome (HCPS) in the Americas and hemorrhagic fever with renal syndrome (HFRS) in Eurasia. Together, these viruses have annually caused approximately 200,000 human infections worldwide in recent years, with a case fatality rate of 5–15% for HFRS and up to 40% for HCPS. There is currently no effective treatment available for either HFRS or HCPS. Only whole virus inactivated vaccines against HTNV or SEOV are licensed for use in the Republic of Korea and China, but the protective efficacies of these vaccines are uncertain. To a large extent, the immune correlates of protection against hantavirus are not known. In this review, we summarized the epidemiology, virology, and pathogenesis of four HFRS-causing viruses, HTNV, SEOV, PUUV, and DOBV, and two HCPS-causing viruses, ANDV and SNV, and then discussed the existing knowledge on vaccines and therapeutics against these diseases. We think that this information will shed light on the rational development of new vaccines and treatments.

Progress on the Prevention and Treatment of Hantavirus Disease

Hantaviruses, members of the order Bunyavirales, family Hantaviridae, have a world-wide distribution and are responsible for greater than 150,000 cases of disease per year. The spectrum of disease associated with hantavirus infection include hemorrhagic fever with renal syndrome (HFRS) and hantavirus pulmonary syndrome (HPS) also known as hantavirus cardiopulmonary syndrome (HCPS). There are currently no FDA-approved vaccines or treatments for these hantavirus diseases. This review provides a summary of the status of vaccine and antiviral treatment efforts including those tested in animal models or human clinical trials.

Three asymptomatic animal infection models of hemorrhagic fever with renal syndrome caused by hantaviruses

Hantaan virus (HTNV) and Puumala virus (PUUV) are rodent-borne hantaviruses that are the primary causes of hemorrhagic fever with renal syndrome (HFRS) in Europe and Asia. The development of well characterized animal models of HTNV and PUUV infection is critical for the evaluation and the potential licensure of HFRS vaccines and therapeutics. In this study we present three animal models of HTNV infection (hamster, ferret and marmoset), and two animal models of PUUV infection (hamster, ferret). Infection of hamsters with a ~3 times the infectious dose 99% (ID99) of HTNV by the intramuscular and ~1 ID99 of HTNV by the intranasal route leads to a persistent asymptomatic infection, characterized by sporadic viremia and high levels of viral genome in the lung, brain and kidney. In contrast, infection of hamsters with ~2 ID99 of PUUV by the intramuscular or ~1 ID99 of PUUV by the intranasal route leads to seroconversion with no detectable viremia, and a transient detection of viral genome. Infection of ferrets with a high dose of either HTNV or PUUV by the intramuscular route leads to seroconversion and gradual weight loss, though kidney function remained unimpaired and serum viremia and viral dissemination to organs was not detected. In marmosets a 1,000 PFU HTNV intramuscular challenge led to robust seroconversion and neutralizing antibody production. Similarly to the ferret model of HTNV infection, no renal impairment, serum viremia or viral dissemination to organs was detected in marmosets. This is the first report of hantavirus infection in ferrets and marmosets.

2'-Fluoro-2'-deoxycytidine is a broad-spectrum inhibitor of bunyaviruses in vitro and in phleboviral disease mouse models

2'-Fluoro-2'-deoxycytidine (2'-FdC) was reported to inhibit various viruses in vitro, including Borna disease, hepatitis C, Lassa fever, influenza and certain herpes viruses, and is inhibitory to influenza viruses in mice. We investigated the antiviral activity of 2'-FdC against several unrelated bunyaviruses in 50% cytopathic effect (CPE) inhibition assays and, with viruses that cause limited CPE, 90% virus yield reduction (VYR) assays. La Crosse (LACV), Maporal, Punta Toro, Rift Valley fever (RVFV), and San Angelo viruses were inhibited in CPE assays at 2.2-9.7 μM concentrations. In VYR assays, Heartland and severe fever with thrombocytopenia syndrome (SFTSV) viruses were inhibited at 0.9 and 3.7 μM, respectively. In contrast, ribavirin inhibited these viruses at an average of 47 μM. Antiviral efficacy studies were also conducted in mice infected with RVFV, SFTSV, and LACV. Against RVFV, 2'-FdC (100 and 200 mg/kg/day) and ribavirin (100 mg/kg/day) treatments each delayed mortality by approximately 6 days compared to placebo. Liver, spleen, and serum viral titers were significantly reduced by antiviral treatments. 2'-FdC (100 and 200 mg/kg/day) prevented death in SFTSV-infected mice, but was not as effective as favipiravir (100 mg/kg/day) based on body weight loss during infection. The 100 mg/kg/day doses of 2'-FdC and favipiravir significantly reduced liver, spleen, and serum viral titers. 2'-FdC and ribavirin afforded no protection against LACV infection in mice, which is encephalitic and thus inherently more difficult to treat. Taken together, our data suggest that 2'-FdC may be a viable candidate for treating certain non-encephalitic bunyavirus infections such as those caused by phleboviruses.

Insufficient efficacy and safety of intravenous ribavirin in treatment of haemorrhagic fever with renal syndrome caused by Puumala virus

BACKGROUND

Intravenous ribavirin has been reported to be an effective treatment for haemorrhagic fever with renal syndrome (HFRS) caused by Hantaan virus in Asia. However, its therapeutic benefits for HFRS caused by Puumala virus (PUUV) in Europe are still unknown.

METHODS

A randomized, open-label study of efficacy and safety of intravenous ribavirin in the treatment of HFRS was conducted in the European part of Russia. Seventy-three patients with suspected HFRS within 4 d of the onset of the disease were randomized to receive either intravenous ribavirin (33 mg/kg, followed by 16 mg/kg given every 6 h for 4 d and by 8 mg/kg given every 8 h for 3 d) plus standard therapy (n = 37) or standard therapy alone (n = 36). The primary outcome was the average change from baseline in viral load over time estimated as area under the viral load curve minus baseline (AUCMB). Fifty-five patients with HFRS confirmed by nested reverse transcriptase - polymerase chain reaction (PCR) assay were included in the assessment of the efficacy. All patients entered into the clinical trial were included in the assessment of the safety.

RESULTS

PUUV was detected in all cases of confirmed HFRS. Viral load kinetics were similar in both treatment groups. Significantly more patients receiving ribavirin than standard therapy experienced low haemoglobin level (95% vs 36%), hyperbilirubinemia (81% vs 3%), sinus bradycardia (43% vs 14%), and rash (19% vs 0%).

CONCLUSIONS

Results of the study showed insufficient efficacy and safety of intravenous ribavirin in the treatment of HFRS caused by PUUV.

Recent advances in hantavirus molecular biology and disease

Hantaviruses are emerging zoonotic pathogens that belong to the Bunyaviridae family. They have been classified as category A pathogens by CDC (centers for disease control and prevention). Hantaviruses pose a serious threat to human health because their infection causes two highly fatal diseases, hemorrhagic fever with renal syndrome (HFRS) and hantavirus cardiopulmonary syndrome (HCPS). These pathogens are transmitted to humans through aerosolized excreta of their infected rodent hosts. Hantaviruses have a tripartite-segmented negative-sense RNA genome. The three genomic RNA segments, S, M, and L, encode a nucleocapsid protein (N), a precursor glycoprotein that is processed into two envelope glycoproteins (Gn and Gc) and the viral RNA-dependent RNA polymerase (RdRp), respectively. N protein is the major structural component of the virus, its main function is to protect and encapsidate the three genomic RNAs forming three viral ribonucleocapsids. Recent studies have proposed that N in conjunction with RdRp plays important roles in the transcription and replication of viral genome. In addition, N preferentially facilitates the translation of viral mRNA in cells. Glycoproteins, Gn and Gc, play major roles in viral attachment and entry to the host cells, virulence, and assembly and packaging of new virions in infected cells. RdRp functions as RNA replicase and transcriptase to replicate and transcribe the viral RNA and is also thought to have endonuclease activity. Currently, no antiviral therapy or vaccine is available for the treatment of hantavirus-associated diseases. Understanding the molecular details of hantavirus life cycle will help in the identification of targets for antiviral therapeutics and in the design of potential antiviral drug for the treatment of HFRS and HCPS. Due to the alarming fatality of hantavirus diseases, development of an effective vaccine against hantaviruses is a necessity.

Lethal disease in infant and juvenile Syrian hamsters experimentally infected with Imjin virus, a newfound crocidurine shrew-borne hantavirus

To gain insights into the pathogenicity of Imjin virus (MJNV), a newfound hantavirus isolated from the Ussuri white-toothed shrew (Crocidura lasiura), groups of Syrian hamsters (Mesocricetus auratus) of varying ages (<1, 5, 10, 14, 21, 35 and 56 days) were inoculated by the intraperitoneal route with 1000 pfu of MJNV strains 04-55 and 05-11. MJNV-infected Syrian hamsters, aged 21 days or less, exhibited reduced activity, weight loss, respiratory distress, hind-limb paralysis and seizures. Death ensued 1 to 6 days after onset of clinical disease. MJNV RNA was detected in brain and other major organs by RT-PCR and real time-PCR. Histopathological examination showed alveolar hemorrhage, interstitial pneumonia and severe pulmonary congestion; focal hepatic necrosis and portal inflammation; and acute meningoencephalitis. By immunohistochemistry, MJNV antigen was detected in pulmonary microvascular endothelial cells and glial cells. Older hamsters (35 and 56 days of age) developed subclinical infection without histopathological changes. Future studies are warranted to determine the pathophysiologic bases for the differential age susceptibility of Syrian hamsters to lethal MJNV disease.

Animal Models for the Study of Rodent-Borne Hemorrhagic Fever Viruses: Arenaviruses and Hantaviruses

Human pathogenic hantaviruses and arenaviruses are maintained in nature by persistent infection of rodent carrier populations. Several members of these virus groups can cause significant disease in humans that is generically termed viral hemorrhagic fever (HF) and is characterized as a febrile illness with an increased propensity to cause acute inflammation. Human interaction with rodent carrier populations leads to infection. Arenaviruses are also viewed as potential biological weapons threat agents. There is an increased interest in studying these viruses in animal models to gain a deeper understating not only of viral pathogenesis, but also for the evaluation of medical countermeasures (MCM) to mitigate disease threats. In this review, we examine current knowledge regarding animal models employed in the study of these viruses. We include analysis of infection models in natural reservoirs and also discuss the impact of strain heterogeneity on the susceptibility of animals to infection. This information should provide a comprehensive reference for those interested in the study of arenaviruses and hantaviruses not only for MCM development but also in the study of viral pathogenesis and the biology of these viruses in their natural reservoirs.

Hantavirus infections

Over the past few decades understanding and recognition of hantavirus infection has greatly improved worldwide, but both the amplitude and the magnitude of hantavirus outbreaks have been increasing. Several novel hantaviruses with unknown pathogenic potential have been identified in a variety of insectivore hosts. With the new hosts, new geographical distributions of hantaviruses have also been discovered and several new species were found in Africa. Hantavirus infection in humans can result in two clinical syndromes: haemorrhagic fever with renal syndrome (HFRS) and hantavirus cardiopulmonary syndrome (HCPS) caused by Old World and New World hantaviruses, respectively. The clinical presentation of HFRS varies from subclinical, mild, and moderate to severe, depending in part on the causative agent of the disease. In general, HFRS caused by Hantaan virus, Amur virus and Dobrava virus are more severe with mortality rates from 5 to 15%, whereas Seoul virus causes moderate and Puumala virus and Saaremaa virus cause mild forms of disease with mortality rates <1%. The central phenomena behind the pathogenesis of both HFRS and HCPS are increased vascular permeability and acute thrombocytopenia. The pathogenesis is likely to be a complex multifactorial process that includes contributions from immune responses, platelet dysfunction and the deregulation of endothelial cell barrier functions. Also a genetic predisposition, related to HLA type, seems to be important for the severity of the disease. As there is no effective treatment or vaccine approved for use in the USA and Europe, public awareness and precautionary measures are the only ways to minimize the risk of hantavirus disease.

Hantaviruses--globally emerging pathogens

Hantaviruses are emerging zoonotic viruses which cause human disease in Africa, America, Asia, and Europe. This review summarizes the progress in hantavirus epidemiology and diagnostics during the previous decade. Moreover, we discuss the influence of ecological factors on the worldwide virus distribution and give an outlook on research perspectives for the next years.

Animal models of viral hemorrhagic fever

The term "viral hemorrhagic fever" (VHF) designates a syndrome of acute febrile illness, increased vascular permeability and coagulation defects which often progresses to bleeding and shock and may be fatal in a significant percentage of cases. The causative agents are some 20 different RNA viruses in the families Arenaviridae, Bunyaviridae, Filoviridae and Flaviviridae, which are maintained in a variety of animal species and are transferred to humans through direct or indirect contact or by an arthropod vector. Except for dengue, which is transmitted among humans by mosquitoes, the geographic distribution of each type of VHF is determined by the range of its animal reservoir. Treatments are available for Argentine HF and Lassa fever, but no approved countermeasures have been developed against other types of VHF. The development of effective interventions is hindered by the sporadic nature of most infections and their occurrence in geographic regions with limited medical resources. Laboratory animal models that faithfully reproduce human disease are therefore essential for the evaluation of potential vaccines and therapeutics. The goal of this review is to highlight the current status of animal models that can be used to study the pathogenesis of VHF and test new countermeasures.

Effectiveness of the ribavirin in treatment of hantavirus infections in the Americas and Eurasia: a meta-analysis

Hemorrhagic fever with renal syndrome (HFRS) and hantavirus pulmonary syndrome (HPS) are transmitted to humans through infection with the old- and new-world hantaviruses, respectively. Together these diseases affect tens of thousands of people every year, and no specific treatment is available. To investigate whether ribavirin treatment for hantaviruses infections decreases disease severity, we conducted a meta-analysis involving human and animal studies. After defining the research protocol and criteria for inclusion/exclusion, we identified seven studies. We found that in groups with HPS who were treated with ribavirin, there was no significant reduction in mortality (RR 0.99, 95 % CI 0.60-1.61, I(2) = 0 %). On the other hand, for animal group with HPS-like disease, there was significant increase in survival (RR 0.05, 95 % CI 0.01-0.34, I(2) = 0 %). For animal group infected with the old-world hantaviruses, treated with ribavirin, there was a statistically significant increase in survival (RR 0.56, 95 % CI 0.42-0.76, I(2) = 64 %). Similarly, for humans with HFRS treated, there was increase in survival (RR 0.28, 95 % CI 0.08-1), although only a study exist. Our meta-analysis provides data that should be interpreted with caution, partly due to the limited number of studies available. Additionally, the results of the application of ribavirin in the population with HPS could not be determined, particularly in patients in the end stage of this disease.

Ribavirin protects Syrian hamsters against lethal hantavirus pulmonary syndrome--after intranasal exposure to Andes virus

Andes virus, ANDV, harbored by wild rodents, causes the highly lethal hantavirus pulmonary syndrome (HPS) upon transmission to humans resulting in death in 30% to 50% of the cases. As there is no treatment for this disease, we systematically tested the efficacy of ribavirin in vitro and in an animal model. In vitro assays confirmed antiviral activity and determined that the most effective doses were 40 µg/mL and above. We tested three different concentrations of ribavirin for their capability to prevent HPS in the ANDV hamster model following an intranasal challenge. While the highest level of ribavirin (200 mg/kg) was toxic to the hamster, both the middle (100 mg/kg) and the lowest concentration (50 mg/kg) prevented HPS in hamsters without toxicity. Specifically, 8 of 8 hamsters survived intranasal challenge for both of those groups whereas 7 of 8 PBS control-treated animals developed lethal HPS. Further, we report that administration of ribavirin at 50 mg/kg/day starting on days 6, 8, 10, or 12 post-infection resulted in significant protection against HPS in all groups. Administration of ribavirin at 14 days post-infection also provided a significant level of protection against lethal HPS. These data provide in vivo evidence supporting the potential use of ribavirin as a post-exposure treatment to prevent HPS after exposure by the respiratory route.

High-dose intravenous methylprednisolone for hantavirus cardiopulmonary syndrome in Chile: a double-blind, randomized controlled clinical trial

BACKGROUND

Andes virus (ANDV)-related hantavirus cardiopulmonary syndrome (HCPS) has a 35% case fatality rate in Chile and no specific treatment. In an immunomodulatory approach, we evaluated the efficacy of intravenous methylprednisolone for HCPS treatment, through a parallel-group, placebo-controlled clinical trial.

METHODS

Patients aged >2 years, with confirmed or suspected HCPS in cardiopulmonary stage, admitted to any of 13 study sites in Chile, were randomized by study center in blocks of 4 with a 1:1 allocation and assigned through sequentially numbered envelopes to receive placebo or methylprednisolone 16 mg/kg/day (≤1000 mg) for 3 days. All personnel remained blinded except the local pharmacist. Infection was confirmed by immunoglobulin M antibodies or ANDV RNA in blood. The composite primary endpoint was death, partial pressure of arterial oxygen/fraction of inspired oxygen ratio ≤55, cardiac index ≤2.2, or ventricular tachycardia or fibrillation within 28 days. Safety endpoints included the number of serious adverse events (SAEs) and quantification of viral RNA in blood. Analysis was by intention to treat.

RESULTS

Infection was confirmed in 60 of 66 (91%) enrollees. Fifteen of 30 placebo-treated patients and 11 of 30 methylprednisolone-treated patients progressed to the primary endpoint (P = .43). We observed no significant difference in mortality between treatment groups (P = .41). There was a trend toward more severe disease in placebo recipients at entry. More subjects in the placebo group experienced SAEs (P = .02). There were no SAEs clearly related to methylprednisolone administration, and methylprednisolone did not increase viral load.

CONCLUSIONS

Although methylprednisolone appears to be safe, it did not provide significant clinical benefit to patients. Our results do not support the use of methylprednisolone for HCPS.

CLINICAL TRIALS REGISTRATION

NCT00128180.

The murine model for Hantaan virus-induced lethal disease shows two distinct paths in viral evolutionary trajectory with and without ribavirin treatment

In vitro, ribavirin acts as a lethal mutagen in Hantaan virus (HTNV)-infected Vero E6 cells, resulting in an increased mutation load and viral population extinction. In this study, we asked whether ribavirin treatment in the lethal, suckling mouse model of HTNV infection would act similarly. The HTNV genomic RNA (vRNA) copy number and infectious virus were measured in lungs of untreated and ribavirin-treated mice. In untreated, HTNV-infected mice, the vRNA copy number increased for 10 days postinfection (dpi) and thereafter remained constant through 26 dpi. Surprisingly, in ribavirin-treated, HTNV-infected mice, vRNA levels were similar to those in untreated mice between 10 and 26 dpi. Infectious virus levels, however, were different: in ribavirin-treated mice, the amount of infectious HTNV was significantly decreased relative to that in untreated mice, suggesting that ribavirin reduced the specific infectivity of the virus (amount of infectious virus produced per vRNA copy). Mutational analysis revealed a ribavirin-associated elevation in mutation frequency in HTNV vRNA similar to that previously reported in vitro. Codon-based analyses of rates of nonsynonymous (dN) and synonymous (dS) substitutions in the S segment revealed a positive selection for codons within the HTNV N protein gene in the ribavirin-treated vRNA population. In contrast, the vRNA population in untreated, HTNV-infected mice showed a lower level of diversity, reflecting purifying selection for the wild-type genome. In summary, these experiments show two different evolutionary paths that Hantavirus may take during infection in a lethal murine model of disease, as well as the importance of the in vivo host environment in the evolution of the virus, which was not apparent in our prior in vitro model system.

The Syrian hamster model of hantavirus pulmonary syndrome

Hantavirus pulmonary syndrome (HPS) is a relatively rare, but frequently fatal disease associated with New World hantaviruses, most commonly Sin Nombre and Andes viruses in North and South America, respectively. It is characterized by fever and the sudden, rapid onset of severe respiratory distress and cardiogenic shock, which can be fatal in up to 50% of cases. Currently there are no approved antiviral therapies or vaccines for the treatment or prevention of HPS. A major obstacle in the development of effective medical countermeasures against highly pathogenic agents like the hantaviruses is recapitulating the human disease as closely as possible in an appropriate and reliable animal model. To date, the only animal model that resembles HPS in humans is the Syrian hamster model. Following infection with Andes virus, hamsters develop HPS-like disease which faithfully mimics the human condition with respect to incubation period and pathophysiology of disease. Perhaps most importantly, the sudden and rapid onset of severe respiratory distress observed in humans also occurs in hamsters. The last several years has seen an increase in studies utilizing the Andes virus hamster model which have provided unique insight into HPS pathogenesis as well as potential therapeutic and vaccine strategies to treat and prevent HPS. The purpose of this article is to review the current understanding of HPS disease progression in Syrian hamsters and discuss the suitability of utilizing this model to evaluate potential medical countermeasures against HPS.

Safety and pharmacokinetics of ribavirin for the treatment of la crosse encephalitis

BACKGROUND

La Crosse viral encephalitis (LACVE) is associated with residual epilepsy and neurocognitive deficits in survivors. This report summarizes 3 phases of clinical studies of children treated with intravenous (IV) ribavirin (RBV), each one exploring a different phase (I, IIA, IIB) of clinical trial development.

METHODS

In phase I, 7 children with life-threatening LACVE were treated with emergency use RBV using a moderate IV dose (8.33 mg/kg/dose q 8 hours day 1, 5 mg/kg/dose q 8 hours days 2-10). In phase IIA, 12 children with severe LACVE were enrolled: 8 treated with RBV (same dose as phase I) and 4 with placebo. In phase IIB an escalated dose was used (33 mg/kg dose 1, then 16 mg/kg/dose q 6 hours for 4 days, and 8 mg/kg/dose q 8 hours for 3 days).

RESULTS

In a group of 15 children treated in phase I and phase IIA, RBV appeared safe at moderate dose, but based on steady-state RBV levels of 9.3 μM, estimated cerebrospinal fluid levels were less than 20% of the EC50 of RBV for LACVE. At the escalated dose used in phase IIB, adverse events occurred, likely related to RBV, and therefore the trial was discontinued. Nevertheless, valuable pharmacokinetic (PK) and safety data were obtained at moderate dose, with potential treatment implications for other indications.

CONCLUSIONS

Although the results do not support the use of RBV for LACVE, this nevertheless is the largest study of antiviral treatment for LACVE to date and the largest pharmacokinetic analysis of IV RBV in children for any indication.

In vitro and in vivo activity of ribavirin against Andes virus infection

Pathogenic hantaviruses are a closely related group of rodent-borne viruses which are responsible for two distinct diseases in humans, hemorrhagic fever with renal syndrome and hantavirus pulmonary syndrome (HPS, otherwise known as hantavirus cardiopulmonary syndrome, HCPS). The antiviral effect of ribavirin against Old World hantaviruses, most notably Hantaan virus, is well documented; however, only a few studies have addressed its inhibitory effect on New World hantaviruses. In the present study, we demonstrate that ribavirin is highly active against Andes virus (ANDV), an important etiological agent of HPS, both in vitro and in vivo using a lethal hamster model of HPS. Treatment of ANDV infected Vero E6 cells with ribavirin resulted in dose-dependent reductions in viral RNA and protein as well as virus yields with a half maximal inhibitory concentration between 5 and 12.5 µg ml⁻¹. In hamsters, treatment with as little as 5 mg kg⁻¹ day⁻¹ was 100% effective at preventing lethal HPS disease when therapy was administered by intraperitoneal injection from day 1 through day 10 post-infection. Significant reductions were observed in ANDV RNA and antigen positive cells in lung and liver tissues. Ribavirin remained completely protective when administered by intraperitoneal injections up to three days post-infection. In addition, we show that daily oral ribavirin therapy initiated 1 day post-infection and continuing for ten days is also protective against lethal ANDV disease, even at doses of 5 mg kg⁻¹ day⁻¹. Our results suggest ribavirin treatment is beneficial for postexposure prophylaxis against HPS-causing hantaviruses and should be considered in scenarios where exposure to the virus is probable. The similarities between the results obtained in this study and those from previous clinical evaluations of ribavirin against HPS, further validate the hamster model of lethal HPS and demonstrate its usefulness in screening antiviral agents against this disease.

Human pathogenic hantaviruses and prevention of infection

Hantaviruses are emerging viruses which are hosted by small mammals. When transmitted to humans, they can cause two clinical syndromes, hemorrhagic fever with renal syndrome or hantavirus cardiopulmonary syndrome. The review compiles the current list of hantaviruses which are thought to be pathogenic in humans on the basis of molecular or at least serological evidence. Whereas induction of a neutralizing humoral immune response is considered to be protective against infection, the dual role of cellular immunity (protection versus immunopathogenicity) is discussed. For active immunisation, inactivated virus vaccines are licensed in certain Asian countries. Moreover, several classical and molecular vaccine approaches are in pre-clinical stages of development. The development of hantavirus vaccines is hampered by the lack of adequate animal models of hantavirus-associated disease. In addition to active immunization strategies, the review summarizes other ways of infection prevention, as passive immunization, chemoprophylaxis, and exposition prophylaxis.

Hantavirus pulmonary syndrome: a concise clinical review

In 1978, hantaviruses were first described as the etiological agent of hemorrhagic fever with renal syndrome (HFRS) in Korea. Since then, numerous related, enveloped, negative-stranded RNA viruses have been identified, forming the genus Hantavirus within the family Bunyaviridae. These pathogens are distributed worldwide and thus can be classified, on the basis of phylogenetic origins, into Old World viruses or New World viruses (ie North, Central, and South America). Similarly, these viruses cause two major types of syndromes, corresponding respectively to their phylogenies: the original HFRS or the more recently described hantavirus pulmonary syndrome (HPS). As the hantavirus pulmonary syndrome is the primary hantaviral disease in North America, it will thus be the focus of this review.

Hantavirus protein interactions regulate cellular functions and signaling responses

Rodent-borne pathogenic hantaviruses cause two severe and often lethal zoonotic diseases: hemorrhagic fever with renal syndrome (HFRS) in Eurasia and hantavirus cardiopulmonary syndrome (HCPS) in the Americas. Currently, no US FDA-approved therapeutics or vaccines are available for HFRS/HCPS. Infections with hantaviruses are not lytic, and it is currently not known exactly why infections in humans cause disease. A better understanding of how hantaviruses interfere with normal cell functions and activation of innate and adaptive immune responses might provide clues to future development of specific treatment and/or vaccines against hantavirus infection. In this article, the current knowledge regarding immune responses observed in patients, hantavirus interference with cellular proteins and signaling pathways, and possible approaches in the development of therapeutics are discussed.

Arenaviruses and hantaviruses: from epidemiology and genomics to antivirals

The arenaviruses and hantaviruses are segmented genome RNA viruses that are hosted by rodents. Due to their association with rodents, they are globally widespread and can infect humans via direct or indirect routes of transmission, causing considerable human morbidity and mortality. Nevertheless, despite their obvious and emerging importance as pathogens, there are currently no effective antiviral drugs (except ribavirin which proved effective against Lassa virus) with which to treat humans infected by any of these viruses. The EU-funded VIZIER project (Comparative Structural Genomics of Viral Enzymes Involved in Replication) was instigated with an ultimate view of contributing to the development of antiviral therapies for RNA viruses, including the arenaviruses and bunyaviruses. This review highlights some of the major features of the arenaviruses and hantaviruses that have been investigated during recent years. After describing their classification and epidemiology, we review progress in understanding the genomics as well as the structure and function of replicative enzymes achieved under the VIZIER program and the development of new disease control strategies.

A global perspective on hantavirus ecology, epidemiology, and disease

Hantaviruses are enzootic viruses that maintain persistent infections in their rodent hosts without apparent disease symptoms. The spillover of these viruses to humans can lead to one of two serious illnesses, hantavirus pulmonary syndrome and hemorrhagic fever with renal syndrome. In recent years, there has been an improved understanding of the epidemiology, pathogenesis, and natural history of these viruses following an increase in the number of outbreaks in the Americas. In this review, current concepts regarding the ecology of and disease associated with these serious human pathogens are presented. Priorities for future research suggest an integration of the ecology and evolution of these and other host-virus ecosystems through modeling and hypothesis-driven research with the risk of emergence, host switching/spillover, and disease transmission to humans.

Randomized, controlled trial of oral ribavirin for Japanese encephalitis in children in Uttar Pradesh, India

BACKGROUND

Japanese encephalitis is associated with high rates of mortality and disabling sequelae. To date, no specific antiviral has proven to be of benefit for this condition. We attempted to determine the efficacy of oral ribavirin treatment for reducing early mortality among children with Japanese encephalitis in Uttar Pradesh, India.

METHODS

Children (age, 6 months to 15 years) who had been hospitalized with acute febrile encephalopathy (a < or =2-week history of fever plus altered sensorium) were tested for the presence of immunoglobulin M antibodies to Japanese encephalitis virus with commercial immunoglobulin M capture enzyme-linked immunosorbent assay. Children with positive results were randomized to receive either ribavirin (10 mg/kg per day in 4 divided doses for 7 days) or placebo syrup through nasogastric tube or by mouth. The primary outcome was early mortality; secondary outcome measures were early (at hospital discharge; normal or nearly normal, independent functioning, dependent, vegetative state, or death) outcome, time to resolution of fever, time to resumption of oral feeding, duration of hospitalization, and late outcome (> or =3 months after hospital discharge). The study was double-blind, and analysis was by intention to treat.

RESULTS

A total of 153 patients were enrolled during a 3-year period; 70 patients received ribavirin, and 83 received placebo. There was no statistically significant difference between the 2 groups in the early mortality rate: 19 (27.1%) of 70 ribavirin recipients and 21 (25.3%) of 83 placebo recipients died (odds ratio, 1.10; 95% confidence interval, 0.5-2.4). No statistically significant differences in secondary outcome measures were found.

CONCLUSIONS

For the dosage schedule used in our study, oral ribavirin has no effect in reducing early mortality associated with Japanese encephalitis.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT00216268 .

Efficacy of arbidol on lethal hantaan virus infections in suckling mice and in vitro

AIM

Arbidol is an immunomodulator that was first developed in Russia. In this study, we report the antiviral activity of arbidol against Hantaan virus (HTNV) in vitro and in vivo.

METHODS

The antiviral activity of arbidol in vitro was determined by plaque-forming assay, ranging from 0.5 to 8 microg/mL. To investigate whether arbidol has an antiviral effect in vivo, suckling BALB/c mice infected with HTNV were treated with arbidol at 24 h before infection with a 5, 10 or 20 mg.kg(-1).d(-1), once per day, for 10 days. On day 12 and 28 post infection (pi), histopathological changes and viral antigen were detected. On days 4, 8, 12, and 16 pi, the viral load of target organs and serum TNF-alpha levels of arbidol-treated animals were determined.

RESULTS

Arbidol was found to have potent inhibitory activity against HTNV when added in vitro before or after viral infection, with a 50% inhibitory concentration (IC(50)) of 0.9 and 1.2 microg/mL, respectively. The 50% lethal dose (LD(50)) of arbidol for suckling mice was 78.42 mg.kg(-1).d(-1). Oral administration of arbidol increased both survival rate and mean time to death (MTD). Treatment with arbidol reduced histopathological changes, decreased viral load and viral antigen levels, and modulated the level of serum TNF-alpha.

CONCLUSION

Arbidol has the ability to elicit protective antiviral activity against HTNV in vivo and in vitro.Acta Pharmacologica Sinica (2009) 30: 1015-1024; doi: 10.1038/aps.2009.53; published online 8 June 2009.

Experience with intravenous ribavirin in the treatment of hemorrhagic fever with renal syndrome in Korea

Results of a clinical study using intravenous (IV) ribavirin for treating Department of Defense personnel with hemorrhagic fever with renal syndrome (HFRS) acquired in Korea from 1987 to 2005 were reviewed to determine the clinical course of HFRS treated with IV ribavirin. A total of 38 individuals enrolled in the study had subsequent serological confirmation of HFRS. Four of the 38 individuals received three or fewer doses of ribavirin and were excluded from treatment analysis. Of the remaining 34 individuals, oliguria was present in one individual at treatment initiation; none of the remaining 33 subjects developed oliguria or required dialysis. The mean peak serum creatinine was 3.46 mg/dl and occurred on day 2 of ribavirin therapy. Both the peak serum creatinine and the onset of polyuria occurred on mean day 6.8 of illness. Reversible hemolytic anemia was the main adverse event of ribavirin, with a >or=25% decrease in hematocrit observed in 26/34 (76.5%) individuals. While inability to adjust for all baseline variables prevents comparison to historical cohorts in Korea where oliguria has been reported in 39-69% cases and dialysis required in approximately 40% HFRS cases caused by Hantaan virus, the occurrence of 3% oliguria and 0% dialysis requirement in the treatment cohort is supportive of a previous placebo-controlled HFRS trial in China where IV ribavirin given early resulted in decreased occurrence of oliguria and decreased severity of renal insufficiency.

Synthesis of 1-beta-D-ribofuranosyl-3-ethynyl-[1,2,4]triazole and its in vitro and in vivo efficacy against Hantavirus

There are no FDA approved drugs for the treatment of hemorrhagic fever with renal syndrome (HFRS), a serious human illnesses caused by hantaviruses. Clinical studies using ribavirin (RBV) to treat HFRS patients suggest that it provides an improved prognosis when given early in the course of disease. Given the unique antiviral activity of RBV and the lack of other lead scaffolds, we prepared a diverse series of 3-substituted 1,2,4-triazole-beta-ribosides and identified one with antiviral activity, 1-beta-d-ribofuranosyl-3-ethynyl-[1,2,4]triazole (ETAR). ETAR showed an EC(50) value of 10 and 4.4 microM for Hantaan virus (HTNV) and Andes virus, respectively. ETAR had weak activity against Crimean Congo hemorrhagic fever virus, but had no activity against Rift Valley fever virus. Intraperitoneally delivered ETAR offered protection to suckling mice challenged with HTNV with a approximately 25% survival at 12.5 and 25mg/kg ETAR, and a MTD of 17.1+/-0.7 days. ETAR was phosphorylated in Vero E6 cells to its 5'-triphosphate and reduced cellular GTP levels. In contrast to RBV, ETAR did not increase mutation frequency of the HTNV genome, which suggests it has a different mechanism of action than RBV. ETAR is an exciting and promising lead compound that will be elaborated in further synthetic investigations as a framework for the rational design of new antivirals for treatment of HFRS.

Treatment of hantavirus pulmonary syndrome

Viruses in the genus Hantavirus can cause one of two serious illnesses when transmitted from rodents to humans: hemorrhagic fever with renal syndrome (HFRS) or hantavirus pulmonary syndrome (HPS). Of the two diseases, HPS is more severe with an approximate 40% mortality across the Americas. The high rate of mortality could be reduced if effective therapeutics could be discovered for treatment of this illness. Herein we review approaches being explored for the discovery of therapeutics for HPS and how they could be employed in treatment and prevention of disease.

Does antiviral therapy have a role in the control of Japanese encephalitis?

Approximately 2 billion people live in countries where Japanese encephalitis (JE) presents a significant risk to humans and animals, particularly in China and India, with at least 700 million potentially susceptible children. The combined effects of climate change, altered bird migratory patterns, increasing movement of humans, animals and goods, increasing deforestation and development of irrigation projects will inevitably lead to further geographic dispersal of the virus and an enhanced threat. Although most human infections are mild or asymptomatic, some 50% of patients who develop encephalitis suffer permanent neurologic defects, and 25% die. Vaccines have reduced the incidence of JE in some countries. No specific antiviral therapy is currently available. Interferon alpha-2a was tested in a double-blind placebo-controlled trial on children with Japanese encephalitis, but with negative results. There is thus a real need for antivirals that can reduce the toll of death and neurological sequelae resulting from infection with JE virus. Here we briefly review the epidemiological problems presented by this virus, the present state of drug development and the contributory role that antiviral therapy might play in developing future control strategies for JE.

Animal models of highly pathogenic RNA viral infections: hemorrhagic fever viruses

A diverse group of highly pathogenic RNA viruses cause a severe multisystemic illness in humans commonly referred to as viral hemorrhagic fever (VHF). Although they can vary widely in clinical presentation, all VHFs share certain features that include intense fever, malaise, bleeding and shock. Effective antiviral therapies for most of the VHFs are lacking. Complicating development of intervention strategies is the relative infrequency and unpredictability of VHF outbreaks making human clinical trials extremely challenging or unfeasible. Therefore, animal models that can recapitulate human disease are essential to the development of effective antivirals and vaccines. In general, a good animal model of VHF will demonstrate systemic dispersion of the virus through infection of mononuclear phagocytes and dendritic cells, which induces the release of inflammatory mediators that increase vascular permeability and facilitate coagulation. The culmination of this process leads to significant loss of plasma volume and terminal hypovolemic shock. Although it is clear that nonhuman primate models are the most faithful to human disease, the more accessible and less costly rodent models, including those based on infection with related surrogate viruses, can reproduce certain components of VHF and can serve as suitable preclinical models for initial development of effective countermeasures. Such models are sufficient for testing of drugs that directly block viral replication, but may be inadequate for evaluating therapies that depend for their success on the activation or inhibition of host responses.

Ribavirin reveals a lethal threshold of allowable mutation frequency for Hantaan virus

The broad spectrum of antiviral activity of ribavirin (RBV) lies in its ability to inhibit IMP dehydrogenase, which lowers cellular GTP. However, RBV can act as a potent mutagen for some RNA viruses. Previously we have shown a lack of correlation between antiviral activity and GTP repression for Hantaan virus (HTNV) and evidence for RBV's ability to promote error-prone replication. To further explore the mechanism of RBV, GTP levels, specific infectivity, and/or mutation frequency was measured in the presence of RBV, mycophenolic acid (MPA), selenazofurin, or tiazofurin. While all four drugs resulted in a decrease in the GTP levels and infectious virus, only RBV increased the mutation frequency of viral RNA (vRNA). MPA, however, could enhance RBV's mutagenic effect, which suggests distinct mechanisms of action for each. Therefore, a simple drop in GTP levels does not drive the observed error-prone replication. To further explore RBV's mechanism of action, we made a comprehensive analysis of the mutation frequency over several RBV concentrations. Of importance, we observed that the viral population reached a threshold after which mutation frequency did not correlate with a dose-dependent decrease in the level of vRNA, PFU, or [RTP]/[GTP] (where RTP is ribavirin-5'-triphosphate) over these same concentrations of RBV. Modeling of the relationship of mutation frequency and drug concentration showed an asymptotic relationship at this point. After this threshold, approximately 57% of the viral cDNA population was identical to the wild type. These studies revealed a lethal threshold, after which we did not observe a complete loss of the quasispecies structure of the wild-type genome, although we observed extinction of HTNV.

Ribavirin, human convalescent plasma and anti-beta3 integrin antibody inhibit infection by Sin Nombre virus in the deer mouse model

The New World hantavirus Sin Nombre virus (SNV) is an aetiological agent for the often-fatal hantavirus cardiopulmonary syndrome (HCPS). There is no disease model for SNV and specific treatments for HCPS do not exist. By using the deer mouse infectious model, the in vivo inhibitory potential of ribavirin, human anti-SNV immune plasma (HIP), an anti-beta3 antibody (ReoPro) and a polyclonal rabbit anti-recombinant nucleocapsid (N) antibody against SNV was investigated. Concurrent intraperitoneal administration of 100 mg ribavirin kg(-1) prevented seroconversion in all mice at day 15 post-inoculation (p.i.). No evidence of infection was detectable by immunohistochemical staining or by quantitative RT-PCR in two of these six mice. Lower doses of ribavirin, between 5 and 50 mg kg(-1), were much less effective at inhibiting infection. Mice given 200 microl aliquots of dilutions as high as 1 : 20 of HIP (neutralizing-antibody titre 800) failed to seroconvert by day 15 p.i. SNV N antigen staining and viral S genome were undetectable in these mice. A subset of mice given higher dilutions of HIP became infected. Treatment with 6 mg ReoPro kg(-1) did not prevent seroconversion, but was able to reduce viral load. Mice treated with 200 microl anti-N antibody or negative human plasma seroconverted when challenged with SNV, and antigen staining and viral loads were comparable to those seen in untreated controls. These results show that ReoPro can lower viral loads and that ribavirin and HIP, but not anti-N antibody, inhibit seroconversion and reduce viral loads in a dose-dependent manner.

Activity of ribavirin against Hantaan virus correlates with production of ribavirin-5'-triphosphate, not with inhibition of IMP dehydrogenase

Ribavirin (RBV) is a broad-spectrum antiviral agent that inhibits the production of infectious Hantaan virus (HTNV). Although the mechanism of action of RBV against HTNV is not understood, RBV is metabolized in human cells to both RBV-5'-monophosphate, which inhibits IMP dehydrogenase, resulting in a decrease in intracellular GTP levels, and RBV-5'-triphosphate (RBV-TP), which could selectively interact with the viral RNA polymerase. To elucidate which activity of RBV was most important to its anti-HTNV activity, the mechanism of action of RBV was studied in Vero E6 cells. Incubation with 10 to 40 mug/ml RBV resulted in a small decrease in GTP levels that was not dose dependent. Increasing the RBV concentration from 10 to 40 mug/ml resulted in a decrease in viral RNA (vRNA) levels and an increase in RBV-TP formation. Mycophenolic acid (MPA), an inhibitor of IMP dehydrogenase, also resulted in a decrease in vRNA levels; however, treatment with MPA resulted in a much greater decrease in GTP levels than that seen with RBV. Treatment with both MPA and RBV resulted in increased reduction of vRNA levels but did not result in enhanced depression of GTP levels. Although guanosine prevented the depression in GTP levels caused by RBV, guanosine only partially prevented the effect of RBV on vRNA levels. These results suggest that the inhibition of IMP dehydrogenase by RBV is of secondary importance to the inhibition of vRNA replication by RBV and that the interaction of RBV-TP with the viral polymerase is the primary action of RBV.

Dobrava, but not Saaremaa, hantavirus is lethal and induces nitric oxide production in suckling mice

Hantaviruses are the causative agents of HFRS and HCPS (hemorrhagic fever with renal syndrome and hantavirus cardiopulmonary syndrome), two severe, and often fatal human diseases. Mortality from HFRS varies between hantaviruses; Hantaan and Dobrava show the highest, Seoul intermediate, and Puumala low mortality. Saaremaa, genetically closely related to Dobrava, is also known to induce HFRS, with low or no mortality. In this study, mice were inoculated with Dobrava and Saaremaa viruses to test for infectibility, lethality, viremia, nitric oxide production and antibody responses. Out of suckling mice intracerebrally inoculated with 50, 500 and 5000 focus-forming units of Dobrava virus, respectively, 1/8, 2/8 and 7/8 died within 18–26 days. In all but one of the lethally infected mice high levels of replicating virus were detected, and most were positive for neutralizing antibodies and showed elevated levels of nitric oxide production. All suckling mice intracerebrally inoculated with 50, 500, or 5000 focus-forming units of Saaremaa virus survived and all seroconverted. Clearly lower viral titers were observed for the Saaremaa virus-inoculated mice, also when sacrificed at day 18 after infection, compared to those in mice that died following Dobrava virus infection. Dobrava, Saaremaa, Puumala and Hantaan virus infections of adult mice were asymptomatic, and the anti-nucleocapsid protein IgG2a/IgG1-titer ratio was higher in mice inoculated with Dobrava virus than in those inoculated with Saaremaa virus. Elevated nitric oxide production was not detected in asymptomatically infected mice, and iNOS−/− mice, like normal mice, cleared viremia. In conclusion, we show that Dobrava virus and Saaremaa virus induce distinct differences in terms of survival, viremia, nitric oxide production and antibody responses in mice.

Potential importance of error catastrophe to the development of antiviral strategies for hantaviruses

Hantaviruses represent an important and growing source of disease emergence in both established and developing countries. The New World hantaviruses have been touted as potential biological weapons because of their lethality to humans and high infectivity as an aerosol. It is also important to acknowledge the threat that hantaviruses can represent to US troops that operate in a foreign territory endemic for hantavirus infection, as was demonstrated in the Korean War. Effective vaccines, immunotherapeutics and antivirals for the prophylaxis or treatment of hantaviral infections are not available. Recent evidence that hantaviruses are prone to error catastrophe opens the door to the development of new therapeutic strategies. Possible future directions for applying lethal mutagenesis as a strategy for the development of novel and more effective antiviral therapies for treatment of hantavirus infections are discussed.

New Ecological Aspects of Hantavirus Infection: A Change of A Paradigm and a Challenge of Prevention- A Review

In the last decades a significant number of so far unknown or underestimated pathogens have emerged as fundamental health hazards of the human population despite intensive research and exceptional efforts of modern medicine to embank and eradicate infectious diseases. Almost all incidents caused by such emerging pathogens could be ascribed to agents that are zoonotic or expanded their host range and crossed species barriers. Many different factors influence the status of a pathogen to remain unnoticed or evolves into a worldwide threat. The ability of an infectious agent to adapt to changing environmental conditions and variations in human behavior, population development, nutrition, education, social, and health status are relevant factors affecting the correlation between pathogen and host. Hantaviruses belong to the emerging pathogens having gained more and more attention in the last decades. These viruses are members of the family Bunyaviridae and are grouped into a separate genus known as Hantavirus. The serotypes Hantaan (HTN), Seoul (SEO), Puumala (PUU), and Dobrava (DOB) virus predominantly cause hemorrhagic fever with renal syndrome (HFRS), a disease characterized by renal failure, hemorrhages, and shock. In the recent past, many hantavirus isolates have been identified and classified in hitherto unaffected geographic regions in the New World (North, Middle, and South America) with characteristic features affecting the lungs of infected individuals and causing an acute pulmonary syndrome. Hantavirus outbreaks in the United States of America at the beginning of the 10th decade of the last century fundamentally changed our knowledge about the appearance of the hantavirus specific clinical picture, mortality, origin, and transmission route in human beings. The hantavirus pulmonary syndrome (HPS) was first recognized in 1993 in the Four Corners Region of the United States and had a lethality of more than 50%. Although the causative virus was first termed in connection with the geographic name of its outbreak region the analysis of the individual viruses indicate that the causing virus of HPS was a genetically distinct hantavirus and consequently termed as Sin Nombre virus. Hantaviruses are distributed worldwide and are assumed to share a long time period of co-evolution with specific rodent species as their natural reservoir. The degree of relatedness between virus serotypes normally coincides with the relatedness between their respective hosts. There are no known diseases that are associated with hantavirus infections in rodents underlining the amicable relationship between virus and host developed by mutual interaction in hundreds of thousands of years. Although rodents are the major reservoir, antibodies against hantaviruses are also present in domestic and wild animals like cats, dogs, pigs, cattle, and deer. Domestic animals and rodents live jointly in a similar habitat. Therefore the transmission of hantaviruses from rodents to domestic animals seems to be possible, if the target organs, tissues, and cell parenchyma of the co-habitat domestic animals possess adequate virus receptors and are suitable for hantavirus entry and replication. The most likely incidental infection of species other than rodents as for example humans turns hantaviruses from harmless to life-threatening pathogenic agents focusing the attention on this virus group, their ecology and evolution in order to prevent the human population from a serious health risk. Much more studies on the influence of non-natural hosts on the ecology of hantaviruses are needed to understand the directions that the hantavirus evolution could pursue. At least, domestic animals that share their environmental habitat with rodents and humans particularly in areas known as high endemic hantavirus regions have to be copiously screened. Each transfer of hantaviruses from their original natural hosts to other often incidental hosts is accompanied by a change of ecology, a change of environment, a modulation of numerous factors probably influencing the pathogenicity and virulence of the virus. The new environment exerts a modified evolutionary pressure on the virus forcing it to adapt and probably to adopt a form that is much more dangerous for other host species compared to the original one.

Hantaviruses: Immunology, Treatment, and Prevention

Hantaviruses are rodent-borne bunyaviruses that are associated with two main clinical diseases in humans: hemorrhagic fever with renal syndrome and hantavirus pulmonary syndrome. It has been suggested that host-related immune mechanisms rather than direct viral cytopathology may be responsible for the principal abnormality (vascular dysfunction) in these syndromes. This review summarizes the current knowledge on hantaviral host immune responses, immune abnormalities, laboratory diagnosis, and antiviral therapy as well as the current approaches in vaccine development.

Viruses of the Bunya- and Togaviridae families: potential as bioterrorism agents and means of control

When considering viruses of potential importance as tools for bioterrorism, several viruses in the Bunya- and Togaviridae families have been cited. Among those in the Bunyaviridae family are Rift Valley fever, Crimean-Congo hemorrhagic fever, hanta, and sandfly fever viruses, listed in order of priority. Those particularly considered in the Togaviridae family are Venezuelan, eastern and western equine encephalitis viruses. Factors affecting the selection of these viruses are the ability for them to induce a fatal or seriously incapacitating illness, their ease of cultivation in order to prepare large volumes, their relative infectivity in human patients, their ability to be transmitted by aerosol, and the lack of measures available for their control. Each factor is fully considered in this review. Vaccines for the control of infections induced by these viruses are in varying stages of development, with none universally accepted to date. Viruses in the Bunyaviridae family are generally sensitive to ribavirin, which has been recommended as an emergency therapy for infections by viruses in this family although has not yet been FDA-approved. Interferon and interferon inducers also significantly inhibit these virus infections in animal models. Against infections induced by viruses in the Togaviridae family, interferon-alpha would appear to currently be the most useful for therapy.

Nucleotide triphosphatase/helicase of hepatitis C virus as a target for antiviral therapy

The RNA nucleoside triphosphatase (NTPase)/helicases represent a large family of proteins that are detected in almost all biological systems where RNA plays a central role. The enzymes are capable of enzymatically unwinding duplex RNA structures by disrupting the hydrogen bonds that keep the two strands together. The strand separating activity is associated with hydrolysis of nucleoside triphosphate (NTP). Because of this, potential specific inhibitors of NTPase/helicases could act by one or more of the following mechanisms: (i) inhibition of NTPase activity by interference with NTP binding, (ii) inhibition of NTPase activity by an allosteric mechanism and (iii) inhibition of the coupling of NTP hydrolysis at the unwinding reaction. There are also other inhibitory mechanisms conceivable, which may involve a modulation of the interaction of the enzyme with its RNA substrate, for example, (iv) the competitive inhibition of RNA binding and (v) the inhibition of the unwinding by sterical blockade of the translocation of the NTPase/helicase along the polynucleotide chain. NTPase/helicase has also been identified in the viral genome of hepatitis C virus (HCV) which is a member of the Flaviviridae family. It is conceivable that the inhibition of the unwinding activity of the enzyme leads to the inhibition of virus replication and this may represent a novel antiviral strategy. This review updates the current spectrum of inhibitors targeting different mechanisms by which the NTPase and/or helicase activities of the HCV NTPase/helicase are inhibited. Consequently, some of the compounds might be important as antiviral agents against HCV.

Hantaan virus infection causes an acute neurological disease that is fatal in adult laboratory mice

Hantaan virus, the etiological agent of Korean hemorrhagic fever, is transmitted to humans from persistently infected mice (Apodemus agrarius), which serve as the primary reservoir. Here we demonstrate that several strains of adult Mus musculus domesticus (C57BL/6, BALB/c, AKR/J, and SJL/J) were susceptible to Hantaan virus infection when infected intraperitoneally. First clinical signs were loss of weight, ruffled fur, and reduced activity, which were followed by neurological symptoms, such as paralyses and convulsions. Within 2 days of disease onset, the animals died of acute encephalitis. PCR analysis indicated a systemic infection with viral RNA present in all major organs. Immunohistochemical and in situ hybridization analyses of postmortem material detected viral antigen and RNA in the central nervous system (predominantly brain), liver, and spleen. In the central nervous system, viral antigen and RNA colocalized with perivascular infiltrations, the predominant pathological finding. To investigate the involvement of the interferon system in Hantaan virus pathogenesis, we infected alpha/beta interferon receptor knockout mice. These animals were more susceptible to Hantaan virus infection, indicating an important role of interferon-induced antiviral defense mechanisms in Hantaan virus pathogenesis. The present model may help to overcome shortcomings in the development of therapeutic and prophylactic measurements against hantavirus infections.