New Research on Calici Viruses
In September 2003, Nilsson et al. first reported that the RNA of norovirus, one of two genera of caliciviridae that infects humans, evolves in vivo. It was suggested that the virus evolves in response to the body’s immune system. As a result of this immune pressure, changes in the virus’s capsid might correspond to a change in the phenotype of the virus, namely certain mutations in the P2 domain of the capsid eliminate the viral helix. In this study, an immunocompromised heart transplant patient was followed for one year, and his stool was tested over time to measure the amino acid changes in the virus during the year. This is the first study to follow one patient and document the RNA evolution in vivo as well as suggest the possibility for immune system mediated viral evolution.
Mikael Nilsson, Journal of Virology, December 2003, p. 13117-13124, Vol. 77, No. 24
Caliciviruses are a major cause of gastroenteritis and are the predominant cause of nonbacterial gastroenteritis in the United States. Although the majority of these cases are caused by food contamination, water contamination and transmission is possible. Because very little virus is required to initiate infection, water contamination is likely, but also very difficult to monitor. An international workshop with 36 researchers addressed the issue of detection of noroviruses in water. The workshop focused on three major issues of detection, namely (1) the problems associated with the collection and processing of water samples; (2) the molecular methods necessary to confirm and detect the virus; and (3) the other methods for detecting the virus. It was concluded that one of the major priorities of research on norovirus detection should be to evaluate the current molecular detection methods and standardize the methods used as well as create an “infective surrogate” or a way to examine noroviruses in culture.
Mohammad R. Karim, The Journal of Infectious Diseases 2004;189:21-28
Cruising with Confidence
Because of the high incidence of gastroenteritis on cruise ships, cruise passengers are opting not to shake hands but to tap forearms to greet one and another. In 2002, 12 out of 22 cruise ship outbreaks of gastroenteritis investigated by the CDC were caused by noroviruses, and poor hygiene and close quarters were cited as the culprits.
Linda Bren, FDA Consumer Magazine, May-June 2003. http://www.fda.gov/fdac/features/2003/303_virus.html
The first case of a Norovirus outbreak being caused by a recreational water fountain was reported in 2004. On a hot summer day 200 school children went to their annual party at a playground. One hundred of those children reported vomiting, diarrhea and stomach pain the next day, and norovirus was the cause. Since most of the children brought their lunches, the most common means of transmission, food, was eliminated and water transmission was implicated. After surveying the parents, it was discovered that many of the children played in the water fountain. Also, the amount of time spent in the fountain correlated with the percentage of cases; the school who spent a longer amount of time in the playground had more children infected compared to the school which left early. In conclusion, this study validates the importance of water testing and the possibility for novel means of transmission.
(Figure 1: Christian 2004)
Christian J. P. A. Hoebe, The Journal of Infectious Diseases: 2004;189:699-705.
It has been shown that different strains of norovirus can attach to the gut with varying efficacy. Namely, some strains are better at attaching to the ABH histo-blood group antigens, the antigens are on the cells lining the gut, than others. Researchers discovered that Norwalk virus binds to H type 1, H type 3, and Le(b) proteins in the gut as well as what proteins other strains of norovirus bind to. However, another interesting aspect of their study is that they discovered some properties of human stool facilitates the binding of the virus to the gut, which helps explain the propensity of fecal-oral transmission.
Harrington PR, J Virol. 2004 Mar 15;78(6):3035-3045