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INFECTIOUS DOSE OF NORWALK VIRUS
Impact/Purpose:
The objective is to determine the dose-response for the Norwalk virus. This information will be used, along with exposure data, to assess microbial risk for this waterborne disease agent (the Norwalk virus has been implicated in 14 recognized outbreaks in the U.S. since 1980). Norwalk virus and other caliciviruses may occur in ground waters as well as surface waters; thus the infectious dose data may be useful in the development of the long-term ESWTR and GWDR.
Description:
The Norwalk virus and related viruses (caliciviruses) have been identified as a common cause of waterborne disease. Moreover, there are many outbreaks of waterborne disease every year where the causative agent was never identified, and it is thought that many of these are due to pathogenic viruses such as the Norwalk agent. No data exist as to how many Norwalk viruses are needed to infect or cause illness in humans. The Norwalk virus is not known to infect animals. To assess risk from these viruses, and therefore to assess the necessary level of control a water system would need in order to maintain an acceptable risk under the long-term ESWTR, the infectious dose data is essential. This project involves feeding studies using healthy human volunteers. In Phase I of the study, 45 volunteers with varying levels of preexisting antibodies were exposed to different doses of Norwalk virus. After dosing, each subject was evaluated for gastrointestinal symptoms, shedding of Norwalk virus in the stool, and antibody seroconversion.