Norovirus - latest news

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.

http://bit.ly/14CQc50

http://www.nhs.uk/conditions/Norovirus/Pages/Introduction.aspx

Border Security in the Gut

A couple of weeks ago, when I was returning to the UK, I chose the electronic passport queue, instead of the normal one. You put your "biometric" passport into a machine and stare into a camera. The computer checks whether your travel-weary features match the ones in the passport. It was extremely slow compared to the human immigration officers in the adjacent queue, who were whipping through British passport holders many times faster. To pass the time, I thought about a comparable process that happens in the gut, in which the immune system checks the identity of passing microbes.

The immune system in the gut is very powerful and there are two reasons. Firstly, the gut is such an inviting, food-rich niche. Millions of microbes have evolved to move in and either live in partnership with us or cause unpleasant intestinal diseases. Also the gut wall has a large, vulnerable surface area that microbes can use as a route to infect other regions of the body - typhoid and polio are examples.

All along the gut lining, defence forces are lined up, ready to repel invaders. Huge numbers of immune cells patrol and antibodies are present in vast quantities. Specialised patches of cells take samples of everything that passes, shuffling their catch of the day inwards for scrutiny. 

This facet of the immune system may remind us of immigration control but it's a lot more complex. The billions of molecules scrutinised daily are much more numerous and varied than human faces. They include:

·      Harmless food molecules

·      New, dangerous microbes encountered for the first time

·      Dangerous microbes that have been previously encountered, for which an antibody has already been manufactured

·      Harmless microbes both familiar and unfamiliar

·      Cells belonging to your own body (cheek cells for instance)

This is a monumental task. Far more demanding than devising an immigration system that could  identify every person on the planet without holding up the queue.

It is very important that the gut does not over-react to the millions of friendly bacteria, because such a reaction could cause inflammation. When there is good cause, inflammation is literally a life-saver, reacting rapidly to bacterial invasion of wounds. Longer-term inflammation, on the other hand, is harmful because the powerful chemicals released cause tissue damage.

It has long been suspected that some kind of imbalance in the way the immune system reacts to friendly bacteria lies behind inflammatory diseases of the gut. Immunologists in the University of Pennsylvania have made an important discovery about how the delicate immune balance in the gut can be disturbed. It seems that some very specialised immune cells known as ILCs are needed to keep other immune cells - T cells - under control in the gut, and prevent them from causing inflammation. When ILCs in mice were disabled, inflammation of the gut developed. It seems that ILCs are the ones that can determine the difference between dangerous and harmless bacteria. So under-performing ILCs may be an important cause of gut inflammation.

Work like this furthers our understanding of inflammation in the gut and may eventually lead to new treatments for a range of chronic inflammatory diseases. Or it may not. Tinkering with one aspect of a complex system like the immune system is fraught with difficulty. However it is undoubtedly another intriguing jigsaw piece that contributes to our understanding of how the immune system does its work.

http://bit.ly/10ouz0l

Food poisoning

I am slowed down by a mild attack of food poisoning. Night before last, slowly mounting nausea drove me from bed to bathroom. Vomited just the once. It was a vivid reminder of the ferocity of gastric hydrochloric acid. I have no doubt it killed the bacteria - but the toxins they emitted are lingering on, along with the immune reaction they provoked. 

Had to struggle through the day yesterday and slept with deep unconsciousness from 8pm 'til 6.30. It's noon on day 2 now and my appetite is still poor and energy levels low. Those bacterial toxins have triggered a tidal wave of immune proteins that have found their way to my brain and are issuing orders. Rest! Eat lightly! Conserve your energy while we deal with the toxins in your body! I am hoping that my immune system will soon complete its job and allow me to return to normal. All I can do is wait.