Common cold virus

[Badger4]

Is it true that there are about 200 strains of the common cold virus and that once you have had one particular strain you are immune to it thereafter? I have heard it said that this is why older people get fewer colds than children because they are immune to more strains having had more colds.

[radiogaga]

the cold virus mutates into stronger strains so if you were visiting someone and had the cold, its possible they may contract a worse cold than you originally had.

[Badger4]

Thank you - but are you saying that there is a more or less indefinite number of strains or is there an upper limit (about 200?).

[radiogaga]

well no as the cold strain mutates its simply evolves into another stronger strain, therefore it remains as one not 2.
so around 200 would be correct

[theprof]

Err I think we'd better start again with this question.

At the last count, around 203 different "species" of viruses can cause the symptoms of the common cold. The most common group are known as the Rhinoviruses, which are responsible for around 30-50% of infections. These are present throughout the year, but tend to be be more prevalent in the colder months in temperate climates.

Another group called Adenoviruses also cause colds in all seasons, but this group is usually responsible for cold epidemics.

There are also other groups of viruses such as Respiratory Synctial Virus (RSV0, Reoviruses, Echo Viruses, Coxsackievirus, Coronaviruses and Parainfluenfluenza virus which are usually around in the Winter. Coronaviruses are another group that cause Winter colds, whilst various Enterovirus species can cause Summer colds.

All of these viruses cause what is known in the medical profession as an Upper Respiratory Tract Infection (URI). The rest of us call it the common cold.

(continued)

[theprof]

Badger4, I'm not certain where you got your information on "strains" from but it's important that you're not misled into thinking that the cold is caused by many different strains of the same virus. This is not true because there is no such thing as "the common cold virus". All the virus types I've listed above can cause the symptoms and sometimes, even bacteria have been known to bring on the symptoms without any virus being present. Chlamydial lung infection for example mimics URI very well.

As far as immunity is concerned, species have what is called serotypes which might loosely be called "strains". However almost all of the species with serotypes can change their form (mutate) within any given year. As a result, even though there are only 200 species, serotypes are virtually infinite, which means that it's impossible to acquire a high percentage of resistance to any group of virus at any given time.

Yes, older people do in general tend to demonstrate a greater resistance per se in temperate climates as they have encountered more of these serotypes in theie lifetime. However, some of the most virulent serotypes such as the one that occurred in the USA in 2006 struck the elderly with devastating effects.

As for immunity from any given serotype, it can vary considerably. Sometimes you'll be immune from the same for a year, other times it can last a lifetime. No one really knows why. Don't be misled into thinking though that you cannot catch a cold from the same causative organism twice in any given year.

[theprof]

Incidentally, it's only fair I point out that that URI infections are not predisposed to accumulative effects. You cannot give a person you visit a "worse" cold by taking yours along to him or her.

[Badger4]

Thank you to everyone and particularly theprof for some very comprehensive answers.

My question was prompted by a comment some months ago from a doctor in the UK's BBC breakfast television programme, and more specifically by the fact that I caught a cold about a month ago and am having real difficulty in shaking it off. This led me to wonder whether it would be possible to create a vaccination from a mixture of different strains - but it sounds not.

Not being a medical doctor, I freely admit that I use terms like strain/variety/species in a very loose and non-specific way.

Many thanks again.

[Wop/tpo]

Completely non-scientific but could older people catch less colds because they are usually retired from work.
They travel less, are not in crowded conditions, possibly dress in warmer clothing, and take more care of themselves.