Clinical Laboratory Values as Early Indicators of Ebola Virus Infection in Nonhuman Primates.

The Ebola virus (EBOV) outbreak in West Africa during 2013-2016 demonstrated the need to improve Ebola virus disease (EVD) diagnostics and standards of care. This retrospective study compared laboratory values and clinical features of 3 nonhuman primate models of lethal EVD to assess associations with improved survival time. In addition, the study identified laboratory values useful as predictors of survival, surrogates for EBOV viral loads, and triggers for initiation of therapeutic interventions in these nonhuman primate models. Furthermore, the data support that, in nonhuman primates, the Makona strain of EBOV may be less virulent than the Kikwit strain of EBOV. The applicability of these findings as potential diagnostic and management tools for EVD in humans warrants further investigation.

Pathogenicity Comparison Between the Kikwit and Makona Ebola Virus Variants in Rhesus Macaques.

Enhanced virulence and/or transmission of West African Ebola virus (EBOV) variants, which are divergent from their Central African counterparts, are suspected to have contributed to the sizable toll of the recent Ebola virus disease (EVD) outbreak. This study evaluated the pathogenicity and shedding in rhesus macaques infected with 1 of 2 West African isolates (EBOV-C05 or EBOV-C07) or a Central African isolate (EBOV-K). All animals infected with EBOV-C05 or EBOV-C07 died of EVD, whereas 2 of 3 EBOV-K-infected animals died. The viremia level was elevated 10-fold in EBOV-C05-infected animals, compared with EBOV-C07- or EBOV-K-infected animals. More-severe lung pathology was observed in 2 of 6 EBOV-C05/C07-infected macaques. This is the first detailed analysis of the recently circulating EBOV-C05/C07 in direct comparison to EBOV-K with 6 animals per group, and it showed that EBOV-C05 but not EBOV-C07 can replicate at higher levels and cause more tissue damage in some animals. Increased virus shedding from individuals who are especially susceptible to EBOV replication is possibly one of the many challenges facing the community of healthcare and policy-making responders since the beginning of the outbreak.

Natural History of Aerosol-Induced Ebola Virus Disease in Rhesus Macaques.

Ebola virus disease (EVD) is a serious global health concern because case fatality rates are approximately 50% due to recent widespread outbreaks in Africa. Well-defined nonhuman primate (NHP) models for different routes of Ebola virus exposure are needed to test the efficacy of candidate countermeasures. In this natural history study, four rhesus macaques were challenged via aerosol with a target titer of 1000 plaque-forming units per milliliter of Ebola virus. The course of disease was split into the following stages for descriptive purposes: subclinical, clinical, and decompensated. During the subclinical stage, high levels of venous partial pressure of carbon dioxide led to respiratory acidemia in three of four of the NHPs, and all developed lymphopenia. During the clinical stage, all animals had fever, viremia, and respiratory alkalosis. The decompensatory stage involved coagulopathy, cytokine storm, and liver and renal injury. These events were followed by hypotension, elevated lactate, metabolic acidemia, shock and mortality similar to historic intramuscular challenge studies. Viral loads in the lungs of aerosol-exposed animals were not distinctly different compared to previous intramuscularly challenged studies. Differences in the aerosol model, compared to intramuscular model, include an extended subclinical stage, shortened clinical stage, and general decompensated stage. Therefore, the shortened timeframe for clinical detection of the aerosol-induced disease can impair timely therapeutic administration. In summary, this nonhuman primate model of aerosol-induced EVD characterizes early disease markers and additional details to enable countermeasure development.

Kikwit Ebola Virus Disease Progression in the Rhesus Monkey Animal Model.

Ongoing Ebola virus disease outbreaks in the Democratic Republic of the Congo follow the largest recorded outbreak in Western Africa (2013-2016). To combat outbreaks, testing of medical countermeasures (therapeutics or vaccines) requires a well-defined, reproducible, animal model. Here we present Ebola virus disease kinetics in 24 Chinese-origin rhesus monkeys exposed intramuscularly to a highly characterized, commercially available Kikwit Ebola virus Filovirus Animal Non-Clinical Group (FANG) stock. Until reaching predetermined clinical disease endpoint criteria, six animals underwent anesthesia for repeated clinical sampling and were compared to six that did not. Groups of three animals were euthanized and necropsied on days 3, 4, 5, and 6 post-exposure, respectively. In addition, three uninfected animals served as controls. Here, we present detailed characterization of clinical and laboratory disease kinetics and complete blood counts, serum chemistries, Ebola virus titers, and disease kinetics for future medical countermeasure (MCM) study design and control data. We measured no statistical difference in hematology, chemistry values, or time to clinical endpoint in animals that were anesthetized for clinical sampling during the acute disease compared to those that were not.

Ebola Virus Causes Intestinal Tract Architectural Disruption and Bacterial Invasion in Non-Human Primates.

In the 2014⁻2016 West Africa Ebola Virus (EBOV) outbreak, there was a significant concern raised about the potential for secondary bacterial infection originating from the gastrointestinal tract, which led to the empiric treatment of many patients with antibiotics. This retrospective pathology case series summarizes the gastrointestinal pathology observed in control animals in the rhesus EBOV-Kikwit intramuscular 1000 plaque forming unit infection model. All 31 Non-human primates (NHPs) exhibited lymphoid depletion of gut-associated lymphoid tissue (GALT) but the severity and the specific location of the depletion varied. Mesenteric lymphoid depletion and necrosis were present in 87% (27/31) of NHPs. There was mucosal barrier disruption of the intestinal tract with mucosal necrosis and/or ulceration most notably in the duodenum (16%), cecum (16%), and colon (29%). In the intestinal tract, hemorrhage was noted most frequently in the duodenum (52%) and colon (45%). There were focal areas of bacterial submucosal invasion in the gastrointestinal (GI) tract in 9/31 (29%) of NHPs. Only 2/31 (6%) had evidence of pancreatic necrosis. One NHP (3%) experienced jejunal intussusception which may have been directly related to EBOV. Immunofluorescence assays demonstrated EBOV antigen in CD68+ macrophage/monocytes and endothelial cells in areas of GI vascular injury or necrosis.

Ebola Virus Infections in Nonhuman Primates Are Temporally Influenced by Glycoprotein Poly-U Editing Site Populations in the Exposure Material.

Recent experimentation with the variants of the Ebola virus that differ in the glycoprotein's poly-uridine site, which dictates the form of glycoprotein produced through a transcriptional stutter, has resulted in questions regarding the pathogenicity and lethality of the stocks used to develop products currently undergoing human clinical trials to combat the disease. In order to address these concerns and prevent the delay of these critical research programs, we designed an experiment that permitted us to intramuscularly challenge statistically significant numbers of naïve and vaccinated cynomolgus macaques with either a 7U or 8U variant of the Ebola virus, Kikwit isolate. In naïve animals, no difference in survivorship was observed; however, there was a significant delay in the disease course between the two groups. Significant differences were also observed in time-of-fever, serum chemistry, and hematology. In vaccinated animals, there was no statistical difference in survivorship between either challenge groups, with two succumbing in the 7U group compared to 1 in the 8U challenge group. In summary, survivorship was not affected, but the Ebola virus disease course in nonhuman primates is temporally influenced by glycoprotein poly-U editing site populations.