In summary, PVM has recently emerged as a useful novel model for the study respiratory disease in mice [7, [27] [28] [29] [30] ; this has provided significant incentive toward identifying tissue culture systems for virus propagation. The mouse RAW 264.7 cell line supports efficient replication of PVM in vitro and responds to infection by augmenting production of cytokines implicated in the pathogenesis of respiratory disease. Use of this ex vivo model of PVM infection will permit further study of biological responses associated with virus infection and the cellular and molecular level.  Designing and conducting tabletop exercises to assess public health preparedness for manmade and naturally occurring biological threats BACKGROUND: Since 2001, state and local health departments in the United States (US) have accelerated efforts to prepare for high-impact public health emergencies. One component of these activities has been the development and conduct of exercise programs to assess capabilities, train staff and build relationships. This paper summarizes lessons learned from tabletop exercises about public health emergency preparedness and about the process of developing, conducting, and evaluating them. METHODS: We developed, conducted, and evaluated 31 tabletop exercises in partnership with state and local health departments throughout the US from 2003 to 2006. Participant self evaluations, after action reports, and tabletop exercise evaluation forms were used to identify aspects of the exercises themselves, as well as public health emergency responses that participants found more or less challenging, and to highlight lessons learned about tabletop exercise design. RESULTS: Designing the exercises involved substantial collaboration with representatives from participating health departments to assure that the scenarios were credible, focused attention on local preparedness needs and priorities, and were logistically feasible to implement. During execution of the exercises, nearly all health departments struggled with a common set of challenges relating to disease surveillance, epidemiologic investigations, communications, command and control, and health care surge capacity. In contrast, performance strengths were more varied across participating sites, reflecting specific attributes of individual health departments or communities, experience with actual public health emergencies, or the emphasis of prior preparedness efforts. CONCLUSION: The design, conduct, and evaluation of the tabletop exercises described in this report benefited from collaborative planning that involved stakeholders from participating health departments and exercise developers and facilitators from outside the participating agencies. While these exercises identified both strengths and vulnerabilities in emergency preparedness, additional work is needed to develop reliable metrics to gauge exercise performance, inform follow-up action steps, and to develop re-evaluation exercise designs that assess the impact of post-exercise interventions. Since 2001, state and local health departments in the US have accelerated efforts to prepare for bioterrorism and other high-impact public health emergencies. These activities have been spurred by federal funding and guidance from the US Centers for Disease Control and Prevention (CDC) and the Health Resources and Services Administration (HRSA) [1] [2] [3] . Over time, the emphasis of this guidance has expanded from bioterrorism to include "terrorism and non-terrorism events, including infectious disease, environmental and occupational related emergencies" [4] as well as pandemic influenza [5] .