Uniformed Services University of the Health Sciences
Department of Pathology
4301 Jones Bridge Road, C1094
Bethesda, Maryland 20814-4799
Phone: (301) 295-3450
fax: (301) 295-1640
My research has centered on biodefense against Ebola virus, which is classed by the CDC as a Category A bioterrorism threat agent. There are at present no effective antiviral agents available for the treatment of Ebola hemorrhagic fever nor have appropriate vaccines been approved for human disease prevention. Despite current concerns regarding the possible aerosolized release of Ebola virus by terrorists, little is known about the capacity of this virus to colonize the human lower respiratory tract, to breach the barrier function of the lungs, and to subsequently induce a systemic viral hemorrhagic fever syndrome. My laboratory has developed a unique in vitro model to study Ebola virus replication in primary cultured human bronchial epithelial cells in air-liquid interface. We have found that Zaire ebolavirus, the most lethal strain of the virus, can replicate and shed infectious particles for at least 3 weeks in these cultures with no apparent adverse effects on the cells, a finding that is distinctly different from that noted in other human cells such as endothelial cells and monocytes/macrophages. To see if these findings can be extrapolated to the in vivo situation, thee cynomolgus macaques were exposed via the aerosol route to 1,000 PFU of Zaire ebolavirus. All three moribund animals were humanely sacrificed on days 5, 6 and 7 after viral challenge. Formalin-fixed sections of trachea, lung, spleen, mediastinal lymph nodes, brain and liver were examined by in situ hybridization to Ebola virus GP antigen mRNA. Evidence of viral replication was detected within tracheal and bronchial respiratory epithelial cells and within alveolar macrophages. Hepatic Kupffer cells and splenic macrophages also displayed evidence of Ebola virus infection. Nitrotyrosine formation also was detected within respiratory epithelial cells, thus corroborating our earlier in vitro findings in cultured human bronchial epithelial cells. These findings indicate that aerosol Zaire ebolavirus challenge can readily induce fatal systemic spread of the virus. Furthermore, aerosolized Ebola virus has a propensity to replicate within the respiratory epithelium and to induce reactive nitrogen species formation within these cells. All these studies were performed in collaboration with Dr. Thomas Geisbert and colleagues in their BSL-4 facility at USAMRIID.
Separately, we have investigated the ability of RNA interference (RNAi) to limit the ability of Ebola to replicate in vivo. Thus, strain 13 guinea pigs were treated with a pool of Zaire ebolavirus L gene specific siRNAs delivered as intraperitoneal polyethylenimine (PEI) polyplexes three hours prior to challenge with 1,000 P.F.U. of Zaire ebolavirus. The PEI siRNA polyplexes reduced plasma viremia levels and partially protected the animals from death. However, evaluation of the same pool of siRNAs delivered in stable nucleic acid-lipid particles (SNALPs) proved that this system was more efficacious, as it completely protected guinea pigs against viremia and death when administered shortly after Zaire ebolavirus challenge. Additional experiments showed that one of the four siRNAs alone could completely protect the guinea pigs from a lethal Zaire ebolavirus challenge. Further development of this technology has the potential to yield effective treatments for Ebola hemorrhagic fever as well as for diseases caused by other agents that are considered to be biological threats.