2000 Progress Report: Studies of the Infectivity of Norwalk and Norwalk-like VirusesEPA Grant Number: R826139
Title: Studies of the Infectivity of Norwalk and Norwalk-like Viruses
Investigators: Moe, Christine L. , Stewart, Paul , Heizer, William , Frelinger, Jeffrey A.
Institution: University of North Carolina at Chapel Hill
EPA Project Officer: Hahn, Intaek
Project Period: January 16, 1998 through January 15, 2001 (Extended to January 15, 2002)
Project Period Covered by this Report: January 16, 1999 through January 15, 2000
Project Amount: $587,842
RFA: Drinking Water (1997) RFA Text | Recipients Lists
Research Category: Water , Drinking Water
Objective:The overall objective of this research is to develop our understanding of the risks associated with exposure to waterborne caliciviruses as a function of dose and host susceptibility factors. Specifically, we will determine the infectious dose of two important human caliciviruses (HuCVs), a prototype Genogroup I virus (Norwalk virus (NV)), and a prototype Genogroup II virus (Snow Mountain Agent (SMA)), which are recognized as major waterborne pathogens. Evidence from outbreaks suggests that these viruses have a very low infectious dose. The results of the proposed study will be valuable for estimating the risk of NV and SMA infection and gastroenteritis associated with exposure to contaminated water, and evaluating the adequacy of current microbiological standards for drinking water. The proposed multi-faceted study constitutes the second phase of a two-part strategy to define the dose-infectivity relationship of NV and a parallel study of the infectivity of SMA. The first phase was a pilot NV dose-ranging study that was supported by the U.S. Environmental Protection Agency (EPA) and completed in 1998. The second phase currently is being conducted at the University of North Carolina. The specific objectives of the second phase are to: (1) identify the dose range of NV and SMA (ID10, ID50, and ID90) in human volunteers with various levels of preexisting antibodies; (2) determine the characteristics of volunteers that are susceptible to infection; and (3) evaluate the fit of several mathematical models of dose-infectivity to our data.
All of the laboratory and data analyses for the pilot NV Dose-Ranging Study and NV Low Dose Study are now complete, and we are preparing a manuscript describing our results for all 76 subjects. We have examined the fit of several dose-response models to the complete NV dataset with 76 subjects. Our preliminary results indicate that NV has a very low infectious dose, and that most infected individuals shed virus for at least 8 days post-challenge. A simple dose-infectivity relationship was not observed. The presence of anti-NV serum IgG in pre-challenge sera was a significant predictor of infection. Based on the results of the dose-response modeling, we calculated a preliminary risk assessment for NV in water using methods and assumptions similar to those of previous investigators and presented these results at the International Calicivirus Workshop in March 1999.
To better understand the immune response of infected subjects, we have used multiple enzyme immunoassays to detect anti-NV serum IgG, IgA, and IgM, and developed methods to examine NV antibodies in feces and saliva. We have developed an enzyme immunoassay for anti-NV IgG and IgA in saliva. This work was presented at the annual meeting of the American Society for Microbiology in May 2000, and we are about to submit a manuscript describing this assay and our results.
In collaboration with Dr. Ralph Baric, University of North Carolina, we cloned the NV capsid gene into Venezuelan Equine Encephalitis virus vector and expressed NV capsid protein that self-assembled into virus-like particles. We have evaluated this expressed protein as antigen for the anti-NV serum IgG EIAs. This work was presented at the annual meeting of the American Society for Virology in July 2000, and we are about to submit a manuscript describing this work.
We obtained inocula for Snow Mountain virus (SMA) and Hawaii Virus (HV) in June 2000 from Dr. John Treanor, University of Rochester, and conducted extensive safety-testing of these inocula during the summer 2000. Both inocula were determined to be free of known enteric pathogens, mycobacteria, HIV, and toxins. The titer of the SMA inoculum was determined by RT-PCR endpoint titration. The SMA dose-ranging study started in October 2000. Subject recruitment and dosing for this phase of the study is ongoing.