The Syrian hamster model of hantavirus pulmonary syndrome

Endothelial cell permeability during hantavirus infection involves factor XII-dependent increased activation of the kallikrein-kinin system

Hemorrhagic fever with renal syndrome (HFRS) and hantavirus pulmonary syndrome (HPS) are diseases caused by hantavirus infections and are characterized by vascular leakage due to alterations of the endothelial barrier. Hantavirus-infected endothelial cells (EC) display no overt cytopathology; consequently, pathogenesis models have focused either on the influx of immune cells and release of cytokines or on increased degradation of the adherens junction protein, vascular endothelial (VE)-cadherin, due to hantavirus-mediated hypersensitization of EC to vascular endothelial growth factor (VEGF). To examine endothelial leakage in a relevant in vitro system, we co-cultured endothelial and vascular smooth muscle cells (vSMC) to generate capillary blood vessel-like structures. In contrast to results obtained in monolayers of cultured EC, we found that despite viral replication in both cell types as well as the presence of VEGF, infected in vitro vessels neither lost integrity nor displayed evidence of VE-cadherin degradation. Here, we present evidence for a novel mechanism of hantavirus-induced vascular leakage involving activation of the plasma kallikrein-kinin system (KKS). We show that incubation of factor XII (FXII), prekallikrein (PK), and high molecular weight kininogen (HK) plasma proteins with hantavirus-infected EC results in increased cleavage of HK, higher enzymatic activities of FXIIa/kallikrein (KAL) and increased liberation of bradykinin (BK). Measuring cell permeability in real-time using electric cell-substrate impedance sensing (ECIS), we identified dramatic increases in endothelial cell permeability after KKS activation and liberation of BK. Furthermore, the alterations in permeability could be prevented using inhibitors that directly block BK binding, the activity of FXIIa, or the activity of KAL. Lastly, FXII binding and autoactivation is increased on the surface of hantavirus-infected EC. These data are the first to demonstrate KKS activation during hantavirus infection and could have profound implications for treatment of hantavirus infections.

Primary manifestations of disease due to hantavirus infections include systemic vascular leakage and hypotension for which the underlying mechanism is not known. A particularly perplexing finding is that the vascular endothelium remains intact during hantavirus infection and with no apparent cytopathic effects to explain leakage and edema. Our studies show for the first time that hantavirus-infected EC have increased KKS activation resulting in liberation of the inflammatory peptide, BK. BK is a potent inducer of vascular permeability, edema formation, and hypotension; thus, our results provide a novel mechanism for hantavirus-induced vascular abnormalities. Additionally, we describe the use of an in vitro capillary blood vessel model to examine responses occurring locally in blood vessels during infection. This model could be used in future studies by others for assessing further aspects of hantavirus pathogenesis or that of other vascular tropic viruses.

Antiviral efficacy of favipiravir against two prominent etiological agents of hantavirus pulmonary syndrome

Hantavirus pulmonary syndrome (HPS) is caused by infection with several Sigmodontinae- and Neotominae-borne hantaviruses and has a case fatality rate of 30 to 50%. Humans often become infected by inhalation of materials contaminated with virus-laden rodent urine or saliva, although human-to-human transmission has also been documented for Andes virus (ANDV). The ability to transmit via aerosolization, coupled with the high mortality rates and lack of therapeutic options, makes the development of medical countermeasures against HPS imperative. In the present study, we evaluated the efficacy of the broad-spectrum antiviral agent favipiravir (T-705) against Sin Nombre virus (SNV) and ANDV, the predominant causes of HPS in North and South America, respectively. In vitro, T-705 potently inhibited SNV and ANDV, as evidenced by decreased detection of viral RNA and reduced infectious titers. For both viruses, the 90% effective concentration was estimated at ≤5 μg/ml (≤31.8 μM). In the lethal ANDV hamster model, daily administration of oral T-705 at 50 or 100 mg/kg of body weight diminished the detection of viral RNA and antigen in tissue specimens and significantly improved survival rates. Oral T-705 therapy remained protective against HPS when treatment was initiated prior to the onset of viremia. No disease model for SNV exists; however, using a hamster-adapted SNV, we found that daily administration of oral T-705 significantly reduced the detection of SNV RNA and antigen in tissue specimens, suggesting that the compound would also be effective against HPS in North America. Combined, these results suggest that T-705 treatment is beneficial for postexposure prophylaxis against HPS-causing viruses and should be considered for probable exposures.

Animal models for highly pathogenic emerging viruses

Exotic and emerging viral pathogens associated with high morbidity and mortality in humans are being identified annually with recent examples including Lujo virus in southern Africa, Severe Fever with Thrombocytopenia Syndrome virus in China and a SARS-like coronavirus in the Middle East. The sporadic nature of these infections hampers our understanding of these diseases and limits the opportunities to design appropriate medical countermeasures against them. Because of this, animal models are utilized to gain insight into the pathogenesis of disease with the overall goal of identifying potential targets for intervention and evaluating specific therapeutics and vaccines. For these reasons it is imperative that animal models of disease recapitulate the human condition as closely as possible in order to provide the best predictive data with respect to the potential efficacy in humans. In this article we review the current status of disease models for highly pathogenic and emerging viral pathogens.

Hamster-adapted Sin Nombre virus causes disseminated infection and efficiently replicates in pulmonary endothelial cells without signs of disease

To date, a laboratory animal model for the study of Sin Nombre virus (SNV) infection or associated disease has not been described. Unlike infection with Andes virus, which causes lethal hantavirus pulmonary syndrome (HPS)-like disease in hamsters, SNV infection is short-lived, with no viremia and little dissemination. Here we investigated the effect of passaging SNV in hamsters. We found that a host-adapted SNV achieves prolonged and disseminated infection in hamsters, including efficient replication in pulmonary endothelial cells, albeit without signs of disease.