A non mouse-adapted dengue virus strain as a new model of severe dengue infection in AG129 mice

Abstract

The spread of dengue (DEN) worldwide combined with an increased severity of the DEN-associated clinical outcomes have made this mosquito-borne virus of great global public health importance. Progress in understanding DEN pathogenesis and in developing effective treatments has been hampered by the lack of a suitable small animal model. Most of the DEN clinical isolates and cell culture-passaged DENV strains reported so far, either require the need for host adaptation, inoculation with a high dose and/or intravenous (iv.) administration to elicit a virulent phenotype in mice, which results at best in a productive infection with none, few or irrelevant disease manifestations, and with mice dying at the peak of viremia.

Here we describe a non mouse-adapted DEN2 virus strain (D2Y98P) that is highly infectious in AG129 mice (lacking interferon-a/? and -? receptors) upon intraperitoneal (ip.) and subcutaneous (sc.) administration. Infection with a high dose (10^7 PFU) of D2Y98P (via the ip. and sc. route) induced a cytokine storm, massive organ damage, and severe vascular leakage, leading to hemorrhage and rapid death of the animals at the peak of viremia. In contrast, very interestingly and uniquely, ip. infection with a low dose of D2Y98P (10^4 PFU) led to asymptomatic viral dissemination and replication in relevant organs, followed by non-paralytic death of the animals few days after virus clearance, similar to the disease kinetic described in DEN-infected patients. Tissue damage and increased vascular permeability but no hemorrhage, were observed only at moribund state of infected animals, suggesting intact vascular integrity, a cardinal feature of DEN shock syndrome. Interestingly, whereas high pro-inflammatory (TNF-a, IL-6 and IFN-?) cytokine levels were detected at the peak of viremia ? during which the extent of tissue damage and vascular leakage was minimal; basal production of these cytokines was instead measured in the animals at moribund state, where tissue damage and vascular leakage were more severe. This observation suggests that other cytokines or other inflammation-independent mechanisms may be responsible for the vascular leakage phenomenon observed in the infected animals at moribund state.

Strikingly, infection with 10^4 PFU of D2Y98P by the sc. route instead, induced clinical manifestations and disease which closely resembled that of the high dose model, indicating that the sc. route of infection is more potent than the ip. route at triggering a virulent phenotype of DEN infection in AG129. Altogether, infection with the D2Y98P strain thus offers the opportunity to further decipher some of the aspects of DEN pathogenesis and provides a new platform for drug and vaccine testing.