The uSSRA responded to the congressional mandate by conducting a semi-quantitative risk assessment on the only two exclusively BSL-4 agents that are on the priority list for work at the NBAF: Hendra virus (HeV) and Nipah virus (NiV). HeV and NiV are paramyxoviruses (Henipavirus genus) that were recognized in the 1990s and produce high-mortality disease in animals and humans (Eaton et al., 2006; Field et al., 2007).

The uSSRA states that the primary objective of the BSL-4 risk assessment is “to identify and characterize the unique risks associated with working with large animals in BSL-4 conditions.” The analysis therefore focuses exclusively on risks associated with handling infected large animals in BSL-4 containment. The uSSRA modeled four potential release pathways (aerosol, solid, liquid, and transference) and developed scenarios in consultation with an international panel of experts in high-containment settings and pathogens (including representatives of the Australian Animal Health Laboratory in Geelong and the Canadian Science Centre for Human and Animal Health in Winnipeg). The committee commends DHS for consulting an international expert panel to delineate the major and unique risks of the BSL-4 environment.

Some risks are inherent to working in a BSL-4 environment, which include the use or manipulation of dangerous pathogens that are highly lethal to humans or animals and for which there are no preventive or therapeutic interventions. Added to those risks are the combination of the presence of large animals in the maximum-containment environment coupled to the difficulty of maneuvering in biocontainment suits and with separate air supplies. These difficulties raise the risk of injuries, disruptions in air supply, and compromised suit integrity from holding pens, animal bites, inoculations, and use of sharp implements during experiments and necropsies. These hazards highlight the importance of having administrative measures in place—including buddy requirements for BSL-4 systems—to ensure recognition and reporting of such breaches and occupational health programs to ensure proper management of personnel.


The committee concurs with the finding in the uSSRA that transference represents the major risk of inadvertent escape for BSL-4 pathogens relative to other release pathways. However, the committee has many concerns about the analysis and found that the uSSRA does not adequately address the overall risks related to work with BSL-4 pathogens; it elaborates on those below.

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