Pathophysiologic and Transcriptomic Analyses of Viscerotropic Yellow Fever in a Rhesus Macaque Model

Abstract

Infection with yellow fever virus (YFV), an explosively replicating flavivirus, results in viral hemorrhagic disease characterized by cardiovascular shock and multi-organ failure. Unvaccinated populations experience 20 to 50% fatality. Few studies have examined the pathophysiological changes that occur in humans during YFV infection due to the sporadic nature and remote locations of outbreaks. Rhesus macaques are highly susceptible to YFV infection, providing a robust animal model to investigate host-pathogen interactions. In this study, we characterized disease progression as well as alterations in immune system homeostasis, cytokine production and gene expression in rhesus macaques infected with the virulent YFV strain DakH1279 (YFV-DakH1279). Following infection, YFV-DakH1279 replicated to high titers resulting in viscerotropic disease with ∼72% mortality. Data presented in this manuscript demonstrate for the first time that lethal YFV infection results in profound lymphopenia that precedes the hallmark changes in liver enzymes and that although tissue damage was noted in liver, kidneys, and lymphoid tissues, viral antigen was only detected in the liver. These observations suggest that additional tissue damage could be due to indirect effects of viral replication. Indeed, circulating levels of several cytokines peaked shortly before euthanasia. Our study also includes the first description of YFV-DakH1279-induced changes in gene expression within peripheral blood mononuclear cells 3 days post-infection prior to any clinical signs. These data show that infection with wild type YFV-DakH1279 or live-attenuated vaccine strain YFV-17D, resulted in 765 and 46 differentially expressed genes (DEGs), respectively. DEGs detected after YFV-17D infection were mostly associated with innate immunity, whereas YFV-DakH1279 infection resulted in dysregulation of genes associated with the development of immune response, ion metabolism, and apoptosis. Therefore, WT-YFV infection is associated with significant changes in gene expression that are detectable before the onset of clinical symptoms and may influence disease progression and outcome of infection.

Frequency of histopathological changes in Howler monkeys ( Alouatta sp.) naturally infected with yellow fever virus in Brazil

“…These changes have previously been described in natural or experimental YF primate infection (2) (9) . In the fi nal stages of YFV infection, hypotension is considered responsible for oliguria and acute tubular necrosis development (1) .…”

“…In the fi nal stages of YFV infection, hypotension is considered responsible for oliguria and acute tubular necrosis development (1) . In Rhesus monkeys, YFV exhibits strong viscerotropism causing severe kidney injuries, promoting hemodynamic changes, azotemia and organ failure (9) . In Howler monkeys, YFV seems to cause renal lesions similar to those observed in humans, and due to their high frequency they are almost certainly involved in the disease pathogenesis and mortality rates.…”

“…Experimental animal models have allowed characterization of the clinical and pathological changes and pathogenesis of yellow fever virus (YFV) infection (9) (10) . These animal models led to the validation of YF histopathological diagnosis patterns that are observed in almost all human cases (4) (5) (8) .…”

Molecular pathogenesis of viral hemorrhagic fever

“…Similarly, administration of IFNγ reduced viremia and hepatitis severity in squirrel monkeys and prolonged survival time in rhesus macaques [101]. Similar to hemorrhagic fever caused by EBOV, YFV infection results in profound lymphopenia and depletion of lymphocytes in germinal centers of spleen, LN tonsils and Peyer’s patches [102,103]. Similar to Ebola hemorrhagic fever, cytokine dysregulation during may mediate lymphopenia, endothelial damage, disseminated intravascular coagulation and circulatory shock observed in the terminal stage of YFV.…”

“…Levels of pro-inflammatory modulators were significantly higher in patients with fatal yellow fever compared to patients who survived [104]. Similarly, levels of IL-6, IFNγ, MCP-1 and IL-15 were elevated in rhesus macaques infected withYFV [103]. Thrombocytopenia, prolonged clotting and prothrombin times have been observed in human patients and nonhuman primates due to diminished liver production of fibrinogen and clotting factors [94,103].…”