The viruses are the leading cause of epidemic acute, non-bacterial gastroenteritis in the United States, yet new research findings have indicated that 29 percent of individuals participating in a study were completely resistant to the representative virus strain, the Norwalk virus. Other participants showed evidence of acquired immunity, the study results indicated.
The findings of the new study, conducted by researchers from the University of North Carolina at Chapel Hill School of Public Health and their colleagues, suggest that individuals may be effectively vaccinated against Norwalk virus and possibly other Noroviruses.
A report on the study appears in the May issue of the journal Nature Medicine.
The elderly and young children are at higher risks of contracting severe Norovirus infections, especially in institutionalized settings. The Norwalk virus is highly infectious and transmitted through person-to-person contact, exposure to contaminated surfaces and ingestion of feces-contaminated food and water.
Communities, family settings, schools, hospitals, the military and cruise ships are especially vulnerable to outbreaks of the virus.
Dr. Ralph Baric, professor of epidemiology at the School of Public Health; lead author Lisa Lindesmith, a laboratory research specialist in epidemiology at the School of Public Health; and colleagues analyzed samples collected during two studies to investigate human susceptibility and resistance to Norwalk virus infection. Volunteers received different doses of the virus, after which 44 percent developed infection. However, those 29 percent of study participants who did not carry a particular gene called FUT2 did not become infected at any dose level.
"Through this research, we were able to define a genetically resistant population," Baric said. "If you do not have a functional copy of the FUT2 gene, you are protected, regardless of how much virus you are exposed to, because it has no door into your system."
In addition, only some of those with the FUT2 gene developed infection. Acquired immunity may explain the difference between the susceptible volunteers who developed infection and those who did not, said Baric. In addition, individuals with group O blood were significantly more susceptible to the virus than those with group A or B blood types, the study indicates.
Study co-investigators include Dr. Christine Moe, formerly of UNC's epidemiology department and now with Emory University's department of international health; Dr. Severine Marionneau, Dr. Jacques LePendu and Dr. Nathalie Ruvoen, all of the Institute of Biology in Nantes, France; Dr. Xi Jiang, of the Cincinnati Children's Hospital Medical Center's department of pediatrics; and Lauren Lindblad and Dr. Paul Stewart of the UNC School of Public Health's department of biostatistics.
The study leaves many questions unanswered, Lindesmith said. "It is not clear whether the protective immunity described in the study represents short-term or long-term immunity, why some susceptible volunteers developed acquired immunity or what frequency of repeated exposures induces protective immunity," she said. "We also don't know whether these observations about Norwalk virus extend to other Noroviruses."
The study's authors encouraged future research involving volunteers susceptible to Norwalk virus, to conclusively demonstrate whether long-term protective immunity to the virus is possible.
"Additional studies with Noroviruses are needed," Baric said. "However, our data suggest that Norovirus vaccines may elicit protective immunity and reduce the substantial disease burden associated with these viruses. We are now working on the development of efficacious Norovirus vaccines."
Once developed, the vaccines could be given to those in the military who travel to countries with reduced standards for water quality, to health-care and day-care workers and to those working in controlled environments such as cruise ships.
Grant funding for the study was provided by the U.S. Environmental Protection Agency, the National Institutes of Health, the N.C. Biotechnology Center, GlaxoSmithKline and the French National Institute for Health and Medical Research.
Photo note:
To download a photo of Baric, click on http://www.unc.edu/news/newsserv/pics/faculty/baric_ralph.jpg.
To download a photo of Lindesmith, click on http://www.unc.edu/news/newsserv/pics/staff/lindesmith_lisa.jpg.
Contact note:
Baric can be reached at 919-966-3895 or rbaric@email.unc.edu
Lindesmith can be reached at
919-966-7991 or lindesmi@email.unc.edu
UNC School of Public Health contact: Lisa Katz, 919-966-7467 or lisa_katz@unc.edu
UNC News Services contact: Deb Saine,
919-962-8415.
Journal
Nature Medicine