Tuesday, 3 July 2007

Colds and the cold

My mum always told me if I didn’t wear socks and shoes and had cold feet I would get a cold! Some evidence suggests that this old wives tale may be true. Adults have about 3-5 cold infections every year (unless you are a student and it is considerably more than this) and the symptoms are so well know and easily recognised that people self diagnose and there are no special tests doctors perform to say you have a cold, they go off these same old symptoms as the public. Saying what is a cold or flu is not easy but flu is much worse than most common colds, but a bad cold could be easily confused with a mild case of flu. Someone’s reaction to an upper respiratory infection depends more on the person (such as there stress level) than the virus that infects them. There are more than 200 serotypes of viruses (viruses with different antigens) that cause the common cold. Once infected by one of them you have antibodies to protect you from it causing another cold but there are plenty more waiting in the wings to hit you the next time exams are approaching. The rhinovirus is the most common cause of the common cold. The symptoms we experience when we get a cold are not the virus damaging us but our body reacting to the virus. Histamine triggers nerves in the noise to fire and tell the brain to make you sneeze and a sore throat is from a small peptide (bradykinin) signalling to nerves to tell you something is wrong. The colour of you lovely mucus changes from clear to yellow to green as more leukocytes (such as neutrophils) are recruited to fight the infection (Eccles, 2005). The majority of infected people are believed to not have any symptoms or only very mild ones. These are called cub-clinical infections and they can spread to others who will develop a full blown cold (Eccles, 2002).

The question is does the cooling of the body’s surfaces increase the chances of you getting a cold. The name cold suggests a link to me. The usual answer to why we get more colds in winter and cold weather is because we all crowd around in close spaces indoors and breath the same air. However I disagree with this. I do not change my habits during the winter and summer, I live in the same house with the same people who stay in the same no matter what the weather and go to school/uni and sit in the same classes with the same amount of people no matter what the weather. So how can you explain why I get more colds in the winter? I guess my mum is right. Because my feet aren’t warm enough…well there is now evidence to support my mum’s theory. Eccles and Johnson (2005) did find that when people put there feet into cold water and were exposed to a virus they were more likely to develop cold symptoms than those who did not have cold feet. But what are the mechanisms that mean cooling of the body’s extremities to let the virus get the upper hand? Vasoconstriction happens when you get cold, therefore less blood flows to the upper airways. This restricts the supply of heat and nutrients to leukocytes that eliminate viruses in a non-specific manor and reduces phagocytosis. Virus replication may also be increased, rhinoviruses replicate better at 33oC than 37oC. This could all cause a sub-clinical infection to become a full blow cold! Runny noise and all. Vasoconstriction helping cause a cold may also explain why some people get more colds than others. It has been shown that people who get more colds a year have a greater vasoconstriction response than those who only get a couple of colds per year (Eccles, 2002).

There are a lot of questions about colds and how they cause disease and how we catch them. But these diseases do not cause a lot of deaths, only reduce work output and the symptoms can be treated directly. I am just interested in what happens when I am ill.


Menelaos Symeonides said...

I always thought that the old wives' tale was true anyway, and the magical biological model in my head was quite similar to the one you're describing. Maybe I should become an immunologist/visionary/inventor/shaman priest?

I just went to a seminar here at uni about dendritic cells. It was very jargon-heavy but I got the main points and a couple of references so I will do a post on it maybe tomorrow, it was very interesting.

James Lloyd said...

one of my fav old wives tales is 'put a metal spoon in your mouth and you will not cry while cutting onions' not even my mum believes that one lol.

You the immunology side. you can explain all the impossible complex stuff i dont have a clue about. I thought the course was intense and hard to get your head around. nothing compared to the real stuff.

Catarina Vicente said...

Sorry to only post a comment now . About all those tales, or better, about old costumes and traditions. When Adrian Harrison showed me the department for the first time, he told me that his ‘hobby’ was to analyse the reason why certain old traditional medicines or cures, e.g. placing a mouldy bread over a wound, actually worked. We shouldn’t underestimate popular knowledge?

James Lloyd said...

very true we shouldnt but some is clearly stupid but others maybe proved right one day.

Menelaos Symeonides said...

Cat, Adrian told me the same thing! I remember initially thinking "ok that is kind of weird" but then I realized that it's pretty cool. I wonder what research he is up to now, maybe I will look him up on pubmed.

James Lloyd said...

he talks about it on open days as tutorial work he sometimes sets about looking up old remedies and looking to see if they work. i remember thinking 'no thanks, that sounds like real hard work.' it is cool though.