Winter vomiting (noro) virus is usually a brief, illness that
lasts for a few days. For the vulnerable though diarhoea and vomiting can be
more serious and if it spreads in institutional environments it can cause big
problems. It transmits very easily – just a few viral particles are all that is
required to infect someone.
We don’t know a great deal about why it is more common in winter or why
an outbreak can appear “out of nowhere”. There is a suspicion that some
individuals can carry the virus in their bodies for a long period. This happens
with some other pathogens that use the faecal-oral route, such as the one that
causes typhoid. In the notorious case of “Typhoid Mary” a cook passed the
infection to a number of people, over a number of years.
A paper published this week has shed new light on the biology of
norovirus. Researchers used a strain of mice that were infected with the virus.
One surprising discovery is that certain antibiotics, if given before
infection, seem to have a protective effect against noro. This has led to the
suspicion that certain gut bacteria can live in symbiotic partnership with the
virus and sustain a long-term infection. This mechanism could facilitate a
reservoir of infection in the community. Kill the bacteria with antibiotics and
you might prevent long term noro infection.
This discovery seems unlikely to lead to antibiotic treatment for the
average case of norovirus. The immune system brings about its own cure, within
a few days. It’s a classic example of a self-limiting illness. Also, trying to
eliminate specific bacteria in the gut is a tricky business – you can kill off
friendly bacteria and leave the field clear for the much more persistent Clostridium
difficile infection. Any headines suggesting a prospect of antibiotic
treatment for noro are misleading.
The other discovery is that there is a specific immune chemical, a
fairly recent discovery, that can attack this virus. The immune system’s
armoury of chemical weapons is vast and there is still a lot to learn about how
individual chemicals interact with specific pathogens. Interferons are a
category that have formed the basis for drug development. As drugs they tend to
be used for serious illnesses. A fairly newly discovered interferon seems to
have had success in eliminating noro infection in mice.
Again this is contributing to the understanding of the virus and the detailed operation of the immune system. In the long term, dosing “carriers” of
norovirus, who are not ill, with a potent interferon-based drug, is unlikely to
prove to be a practical proposition.
The best defence agains noro virus is hygiene. Wash hands regularly during the winter and if anyone in the family is ill, use diluted bleach to swab down bathroom surfaces.
