Mice catch cruise-ship virus
Cousin of Norwalk-like virus could help fight outbreaks.
7 March 2003

HELEN PEARSON

Last year, a humble virus achieved notoriety when it ruined Americans' dream vacations. Now scientists have begun to understand the culprit by recreating the infection in mice.

Late last year, outbreaks of Norwalk-like virus sent cruise ship passengers to their cabins with vomiting and diarrhea. Military camps, hospitals, even church picnics, regularly fall foul of the pathogen that each year affects around 23 million people and kills 300 in the US alone. It jumps from infected faeces to the mouth via food or contaminated surfaces.

Now Herbert Virgin and his colleagues have identified a cousin of Norwalk-like virus that lurks in mice, which should make infection far easier to study. "We're so excited about it," he says.

Already the team, at Washington University School of Medicine in St Louis, Missouri, has found one possible reason that people fail to build up resistance to repeated infections.

In mice at least, the branch of the immune system that remembers and fights specific pathogens is not enough to prevent a lethal virus infection. The team studied animals genetically engineered to lack particular immune molecules1.

"A mouse model is potentially a big breakthrough," says virologist Mary Estes of Baylor College of Medicine in Houston, Texas. But the mouse and human viruses are not identical, she warns; infected mice, for example, do not suffer gastrointestinal problems.

Ultimately, scientists hope to develop a vaccine against Norwalk-like virus for vulnerable hospital staff or the elderly. "Even travellers might want to take it," Estes says.

Cruise control

The explosion of outbreaks on cruise ships has continued into 2003 - despite the best efforts to scrub and disinfect them. So far, however, investigators are unclear whether there has been a genuine rise in the number of infections, or whether it is simply that more are being reported.

Despite its prevalence, the virus has proved almost impossible to study - because human strains cannot be grown in many lab animals or cells. Scientists have resorted to filtering the virus from diarrhoea - and feeding it to human volunteers.

Virgin stumbled on the mouse version when some of his mice started dying in their cages. The team identified the perpetrator by searching for viral genetic sequences amongst those of the mouse.