The mosquito-borne disease dengue (DEN) is caused by four serologically and genetically related viruses, termed DENV-1 to DENV-4. Infection with one DENV usually leads to acute illness and results in lifelong homotypic immunity, but individuals remain susceptible to infection by the other three DENVs. The lack of a small-animal model that mimics systemic DEN disease without neurovirulence has been an obstacle, but DENV-2 models that resemble human disease have been recently developed in AG129 mice (deficient in interferon alpha/beta and interferon gamma receptor signaling). However, comparable DENV-1, -3, and -4 models have not been developed. We utilized a non-mouse-adapted DENV-3 Thai human isolate to develop a lethal infection model in AG129 mice. Intraperitoneal inoculation of six to eight-week-old animals with strain C0360/94 led to rapid, fatal disease. Lethal C0360/94 infection resulted in physical signs of illness, high viral loads in the spleen, liver, and large intestine, histological changes in the liver and spleen tissues, and increased serum cytokine levels. Importantly, the animals developed vascular leakage, thrombocytopenia, and leukopenia. Overall, we have developed a lethal DENV-3 murine infection model, with no evidence of neurotropic disease based on a non-mouse-adapted human isolate, which can be used to investigate DEN pathogenesis and to evaluate candidate vaccines and antivirals. This suggests that murine models utilizing non-mouse-adapted isolates can be obtained for all four DENVs. IMPORTANCE Dengue (DEN) is a mosquito-borne disease caused by four DENV serotypes (DENV-1, -2, -3, and -4) that have no treatments or vaccines. Primary infection with one DENV usually leads to acute illness followed by lifelong homotypic immunity, but susceptibility to infection by the other three DENVs remains. Therefore, a vaccine needs to protect from all four DENVs simultaneously. To date a suitable animal model to mimic systemic human illness exists only for DENV-2 in immunocompromised mice using passaged viruses; however, models are still needed for the remaining serotypes. This study describes establishment of a lethal systemic DENV-3 infection model with a human isolate in immunocompromised mice and is the first report of lethal infection by a nonadapted clinical DENV isolate without evidence of neurological disease. Our DENV-3 model provides a relevant platform to test DEN vaccines and antivirals.

With over 3.5 billion people at risk and approximately 390 million human infections per year, dengue virus (DENV) disease strains health care resources worldwide. Previously, we and others established models for DENV pathogenesis in mice that completely lack subunits of the receptors (IfnarandIfngr) for type I and type II interferon (IFN) signaling; however, the utility of these models is limited by the pleotropic effect of these cytokines on innate and adaptive immune system development and function. Here, we demonstrate that the specific deletion ofIfnarexpression on subsets of murine myeloid cells (LysM Cre⁺Ifnar^flox/flox[denoted asIfnar^f/fherein]) resulted in enhanced DENV replicationin vivo. The administration of subneutralizing amounts of cross-reactive anti-DENV monoclonal antibodies to LysM Cre⁺Ifnar^f/fmice prior to infection with DENV serotype 2 or 3 resulted in antibody-dependent enhancement (ADE) of infection with many of the characteristics associated with severe DENV disease in humans, including plasma leakage, hypercytokinemia, liver injury, hemoconcentration, and thrombocytopenia. Notably, the pathogenesis of severe DENV-2 or DENV-3 infection in LysM Cre⁺Ifnar^f/fmice was blocked by pre- or postexposure administration of a bispecific dual-affinity retargeting molecule (DART) or an optimized RIG-I receptor agonist that stimulates innate immune responses. Our findings establish a more immunocompetent animal model of ADE of infection with multiple DENV serotypes in which disease is inhibited by treatment with broad-spectrum antibody derivatives or innate immune stimulatory agents.IMPORTANCEAlthough dengue virus (DENV) infects hundreds of millions of people annually and results in morbidity and mortality on a global scale, there are no approved antiviral treatments or vaccines. Part of the difficulty in evaluating therapeutic candidates is the lack of small animal models that are permissive to DENV and recapitulate the clinical features of severe human disease. Using animals lacking the type I interferon receptor only on myeloid cell subsets, we developed a more immunocompetent mouse model of severe DENV infection with characteristics of the human disease, including vascular leakage, hemoconcentration, thrombocytopenia, and liver injury. Using this model, we demonstrate that pathogenesis by two different DENV serotypes is inhibited by therapeutic administration of a genetically modified antibody or a RIG-I receptor agonist that stimulates innate immunity.

Dengue is a mosquito-borne disease of global public health significance that is caused by four serologically and genetically related viruses (DENV-1 to DENV-4). Most human DENV infections are asymptomatic, but clinical cases can range in severity from a relatively mild self-limiting illness to a severe life-threatening disease. Infection with one serotype of DENV results in life-long homotypic immunity but only short term heterotypic protection. There are no licensed vaccines or antivirals for dengue due in part to difficulty in developing small animal models that mimic the systemic disease seen in humans. Consequently, an important advance was the description of models of DENV-2 infection in AG129 mice (deficient in interferon alpha/beta and gamma receptor signaling) that resemble human disease. However, the need for well characterized models of disease due to DENV-1, -3, and -4 still remains. Here we describe a new AG129 mouse model utilizing a non-mouse-adapted Thai human DENV-4 strain 703-4. Following intraperitoneal challenge, animals experience a rapidly progressive lethal infection without developing neurologic clinical signs of disease. High virus titers are seen in multiple visceral tissues including the liver, spleen and large intestine, and the infected animals develop vascular leakage and thrombocytopenia, hallmarks of human dengue. Taken together, our studies demonstrate that this model is an important addition to the field of dengue research particularly in understanding similarities and differences in the pathologic basis of the disease caused by different DENV serotypes and in determining comparative efficacy of putative vaccines and antivirals.

Dengue is a mosquito-borne disease caused by four related but distinct dengue viruses, DENV-1 to DENV-4. Dengue is endemic in most tropical countries, and over a third of the world's population is at risk of being infected. Although the global burden is high, no vaccine or antiviral is licensed to combat this disease. An obstacle complicating dengue research is the lack of animal challenge models that mimic human disease. Advances in immunocompromised murine infection models resulted in development of lethal DENV-2, DENV-3 and DENV-4 models in AG129 mice, which are deficient in both the IFN-α/β receptor (IFN-α/βR) and the IFN-γ receptor (IFN-γR). These models mimic features of dengue disease in humans. Here, we characterized lethal infection of AG129 mice by DENV-4 strain TVP-376 and found that AG129 mice developed clinical signs of illness and high viral loads in multiple tissues and succumbed 5 days after infection. Moreover, the splenic and hepatic histopathology of TVP-376-infected mice demonstrated the presence of cell activation and destruction of tissue architecture. Furthermore, infected mice had heightened levels of circulating cytokines. Comparison of the virulence phenotypes of DENV-4 strain TVP-376 and DENV-2 strain D2S10 revealed that TVP-376-induced mortality occurred in the absence of both IFN-α/βR and IFN-γR signalling, but not with intact signalling from the IFN-γR, whereas D2S10 required the absence of IFN-α/βR signalling only, indicating that it is more virulent than TVP-376. In conclusion, TVP-376 is lethal in AG129 mice, and this model provides a useful platform to investigate vaccine candidates and antivirals against DENV-4.