Atypical Ebola Virus Disease in a Nonhuman Primate following Monoclonal Antibody Treatment Is Associated with Glycoprotein Mutations within the Fusion Loop.

Ebola virus (EBOV) is responsible for numerous devastating outbreaks throughout Africa, including the 2013-2016 West African outbreak as well as the two recent outbreaks in the Democratic Republic of the Congo (DRC), one of which is ongoing. Although EBOV disease (EVD) has typically been considered a highly lethal acute infection, increasing evidence suggests that the virus can persist in certain immune-privileged sites and occasionally lead to EVD recrudescence. Little is understood about the processes that contribute to EBOV persistence and recrudescence, in part because of the rarity of these phenomena but also because of the absence of an animal model that recapitulates them. Here, we describe a case of EBOV persistence associated with atypical EVD in a nonhuman primate (NHP) following inoculation with EBOV and treatment with an experimental monoclonal antibody cocktail. Although this animal exhibited only mild signs of acute EVD, it developed severe disease 2 weeks later and succumbed shortly thereafter. Viremia was undetectable at the time of death, despite abundant levels of viral RNA in most tissues, each of which appeared to harbor a distinct viral quasispecies. Remarkably, sequence analysis identified a single mutation in glycoprotein (GP) that not only resisted antibody-mediated neutralization but also increased viral growth kinetics and virulence. Overall, this report represents the most thoroughly characterized case of atypical EVD in an NHP described thus far, and it provides valuable insight into factors that may contribute to EBOV persistence and recrudescent disease. Ebola virus remains a global threat to public health and biosecurity, yet we still know relatively little about its pathogenesis and the complications that arise following recovery. With nearly 20,000 survivors from the 2013-2016 West African outbreak, as well as over 1,000 survivors of the recent outbreak in the DRC, we must consider the consequences of virus persistence and recrudescent disease, even if they are rare. In this study, we describe a case of atypical Ebola virus disease in a nonhuman primate after treatment with a monoclonal antibody. Not only does this study underscore the potential for atypical disease presentations, but it also emphasizes the importance of considering how medical countermeasures might relate to these phenomena, especially as antibodies are incorporated into the standard of care. The results presented herein provide a foundation from which we can continue to investigate these facets of Ebola virus disease.