Researchers discover how noroviruses cause repeated outbreaks of 'stomach flu'

Norovirus, a common cause of gastroenteritis ("stomach flu"), could potentially be controlled by a vaccine. But because the virus evolves to avoid the immune system, the vaccine might have to be modified from year to year, according to new research published in PLoS Medicine by Ralph Baric of the University of North Carolina, Chapel Hill, and colleagues.

Noroviruses, which are highly contagious, cause nausea, vomiting, and diarrhea. While most people recover within a few days, the very young and old may experience severe disease. Although maintaining hydration is essential, there is no specific treatment for infection.

As with influenza, epidemics of norovirus infection occur periodically (often in closed communities such as cruise ships), and most people have several norovirus infections during their lifetime. This winter the UK has seen almost twice as many norovirus cases compared to the same period last year.

Noroviruses infect cells after attaching to molecules called histo-blood group antigens (HBGA) present on the cell surface. HBGAs comprise a family of complex sugar molecules that exist in great variety among human beings. The researchers found that this variety provides the key to understanding how norovirus outbreaks continue to occur, even in populations that have previously been exposed to noroviruses and therefore harbor antibodies against them.

By analyzing noroviruses isolated from several outbreaks, the researchers found that the viruses evolved to avoid attack by antibodies the hosts developed against them. Over time, some viruses selected in this way attain a shape that enables them to bind to one of the other forms of HBGA, and thereafter are not only resistant to previously existing antibodies, but are also able to infect cells carrying that particular form of HBGA. These viruses can then cause a new outbreak, and the cycle repeats itself.

This continuing evolution of new replacement strains suggests that vaccines could be designed to protect against norovirus infection, but that, as with influenza vaccines, ongoing epidemiologic surveillance and reformulations of norovirus vaccines will be needed.

In a related perspective article, Ben Lopman and colleagues at the UK Health Protection Agency, who were not involved in the study, discuss the evolution of noroviruses and the implications of this research for the control of future outbreaks.

Citation: Lindesmith LC, Donaldson EF, LoBue AD, Cannon JL, Zheng DP, et al. (2008) Mechanisms of GII.4 norovirus persistence in human populations. PLoS Med 5(2): e31. (http://medicine.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pmed.0050031)

Source: PLoS

Related stories:

FDA: Irradiating spinach, lettuce OK to kill germs
(AP) -- Consumers worried about salad safety may soon be able to buy fresh spinach and iceberg lettuce zapped with just enough radiation to kill E. coli and a few other germs.
Researchers discover primary sensor that detects stomach viruses
Scientists at Washington University School of Medicine in St. Louis have identified the primary immune sensor that detects the presence of stomach viruses in the body. They show that the sensor – a protein called MDA-5 – triggers an immune response that revs up the body's defenses to fight off the infection. This knowledge may help develop a treatment that prevents or reduces infection, the researchers suggest in their study, published July 18th in the open-access journal PLoS Pathogens.
Vaccine for stomach flu may be possible, research shows
Every year, millions of people are infected with noroviruses - commonly called “stomach flu” – often resulting in up to 72 hours of vomiting and diarrhea. While most people recover in a few days, the symptoms can lead to dehydration and - in rare cases, especially among the elderly and infants - death.
Six simple steps to protect against and stop the spread of noroviruses
Recent outbreaks of norovirus–also known as stomach flu–indicate the highly contagious, fast-moving virus is again a public health concern. The Association for Professionals in Infection Control and Epidemiology (APIC) has six simple steps to protect families against noroviruses.
Norwalk virus: 'Cruise ship' illness challenging and costly to hospitals, too
A review of measures taken to address a 2004 outbreak of the highly infectious Norwalk virus at The Johns Hopkins Hospital has provided the first solid documentation of expenses and efforts in the United States to stop the infection from spreading among patients, staff and visitors. Total hospital costs for the three-month outbreak - including extra cleaning supplies, staff sick leave, diagnostic tests, replacement staff, and salaries and lost revenue from closed beds - were estimated at more than $650,000.
Sea coral hope for fighting gastroenteritis
A molecule found in coral is effective in fighting the type of virus that causes gastroenteritis, giving hope for the development of better treatments for the illness, according to new research. At present, treatments do not fight the virus itself but instead address its symptoms, such as dehydration and diarrhoea.
If you don't want to fall ill this Christmas, then share a festive kiss but don't shake hands
We've all heard people say 'I won't kiss you, I've got a cold'. But a report just published warns that we may be far more at risk of passing on an infection by shaking someone's hand than in sharing a kiss.
Norovirus suspected in school outbreak
A highly contagious stomach virus sickened more than 100 students and staff at a suburban Chicago high school this week.

News discussion:

Medicine & Health news