Dear Readers, this week I have been suffering from a rather pernicious head cold, which has laid me low and prevented me from exploring my half-mile territory. A commonplace experience (the average adult will suffer from two to four colds every year), but it got me thinking. What causes a cold? How do our typical symptoms (sore throat, runny nose, raised temperature, sneezing) relate to the infection? And what, if anything, can we do to prevent the disease, and to treat it once we have it? I am full of questions, and have tried to find some answers. If you are a doctor, a virologist, a nurse or indeed anyone who can add to my knowledge of this fascinating subject (which is pretty much everybody), please feel free to chip in.
To start at the beginning: colds are caused viruses. A virus is not technically ‘alive’ – some scientists think of them as being on the edge of life – because they fail two crucial tests – they are not made up of cells, and they do not perform many of the key requirements of life, such as respiration, digestion or excretion. When a virus is outside of a host, it is known as a virion, and is made up of only two or three elements – a strand of genetic material (DNA or RNA) and a layer of protein that protects it (known as the capsid). Some viruses also have a layer of lipid (fat) on top of the capsid. Viruses are tiny – an average virus is only one-hundredth the size of a bacteria – and it wasn’t until the age of the electron microscope that we began to understand their myriad forms.
The main virus that causes the common cold is a kind of rhinovirus (rhino meaning ‘nose’, as in rhinoceros (‘nose horn’)). 99 varieties of rhinovirus have been identified so far, and they share an icosahedral (twenty-faceted) shape. They are tiny viruses, just one tenth of the size of a smallpox virus. The best temperature for them to reproduce is about ten degrees colder than human body temperature, which may be one reason why they generally set up operations in the nose – the constant flow of cold air keeps this part of the body colder than others. Plus, it might also explain why colds seem to be commoner in the winter, and after people have become chilled. But this is not the whole story.
Colds are spread by sneezing, coughing and contaminated surfaces . And from September onwards, when children go back to school, any parent will be under siege from the many diseases of their little ones. With their under-developed immune systems, children catch up to 8 colds per year, and I suspect it sometimes feels as if it’s just one long bout of sniffling. If you travel on public transport you are bombarded with other people’s explosive sneezes and hacking coughs. Plus in winter we huddle together indoors and contaminate one another. Really, it’s a wonder that any of us make it through to the summer without a cold.
Incidentally, the virus moves fast: it can start its work of adhering to our cells within 15 minutes of entering our nose, and over 50% of individuals who encounter the virus will be thoroughly infected within two days.
But what happens when we are infected with a virus? A virus’s sole aim in life is to reproduce, and to do that it needs your cells. The virus bonds with a cell, using the proteins on its capsid to infiltrate the cell membrane. Once in, it hijacks the cell’s genetic material, and produces many copies of itself. Eventually, the cell lyses (explodes) and all the new viruses are thrown into the body, to go hunting for more cells to damage. However, a cell sends out distress signals to our immune system using chemicals called cytokines and chemokines. The first response is inflammation, which explains why the first thing that I usually know about an infection is a sore throat.
Other symptoms of a cold are also caused not by the virus itself, but by our body’s response to the infection. Take fever, for example.The role of fever in illness is controversial, but one school of thought suggests that a rise in temperature (triggered by those cytokines) speeds up some of the body’s protective chemical reactions. In the case of a cold, we can also see how the rhinoviruses would be inconvenienced by having the body temperature go up.You could argue that by taking drugs that reduce your fever, you are prolonging the duration of the cold. However, some of us are in a position to lay about and recover naturally, and some of us have to drag ourselves off to work or risk losing our jobs or letting people down, so taking the Night or Day Nurse medication is basically down to pragmatic concerns.
Similarly, colds produce a very unpleasant runny nose, again due to the inflammation caused as a response to the virus by the cytokines – our noses produce mucus to sooth the damage, as I can testify. Couple this with sneezing (a response to the irritation caused by the inflammation) and we have a perfect system for spreading the cold virus. A typical sneeze can produce 40,000 droplets, each one full of happy virions looking for a new home. The advice these days is to sneeze into your elbow if you can manage the manoeuvre in time. Certainly, sneezing into your hand is a great way of spreading it to your fellow commuters or classmates, as the virus can survive outside the human body for three days in the correct conditions. It’s a good reason for washing your hands after travelling, and for trying to make sure that you don’t rub your eyes, bite your nails or suck your thumb.
The common cold has been with us forever, I suspect: the first recorded mention of the disease is in the Eber papyrus, the very first ‘medical textbook’ which was written in ancient Egypt. However, what we can do about it remains uncertain. Prevention of the infection by handwashing is important, but the jury is out on Vitamin C, echinacea, and garlic. Some of you may be old enough to remember the Common Cold Unit, which was set up to investigate the disease in 1946. It was possible to go for a ‘holiday’, all expenses paid, the price being your infection with a common cold virus. It finally shut in 1989, and the only therapy that proved at all efficacious in reducing the duration and severity of symptoms was the use of zinc gluconate lozenges, so this might be worth trying if you feel a cold coming on. For me, it’s all about drinking lots of hot fluids, resting as much as my work schedule will allow, and keeping lots of tissues on hand. Most of us now recognise that going to the doctors is a waste of time and only exposes ourselves and other people to further infection. Fortunately the medical profession, in the UK at least, is much less likely to give out antibiotics for a viral infection than it was in previous decades, which will hopefully help to reduce the growth of antibiotic-resistant bacteria.
There are, however, situations when a cold can lead to something much worse. In the very young, the very elderly or those who are immunocompromised, a cold can be a harbinger of pneumonia, as in the rather chilling poster below. For most of us, a cold is a minor inconvenience, but for others it can be devastating. This is one reason why I never visit my parents if I have a streaming cold – for people with COPD or other respiratory problems, the last thing they need is to be infected with my rhinoviruses. Prevention really is better than cure.
Photo One (Rhinovirus) – By No machine-readable author provided. Robin S assumed (based on copyright claims). – No machine-readable source provided. Own work assumed (based on copyright claims)., CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=1867087
Photo Two (Measles virus) – By Deposition authors: Gutsche, I., Desfosses, A., Effantin, G., Ling, W.L., Haupt, M., Ruigrok, R.W.H., Sachse, C., Schoehn, G.;visualization author: User:Astrojan – http://www.rcsb.org/pdb/explore/explore.do?structureId=4uft, CC BY 4.0, https://commons.wikimedia.org/w/index.php?curid=50091685
Photo Three (Ebola virus) – by CDC Global https://www.flickr.com/photos/cdcglobal/14723720857
Photo Four (Toy Cold Viruses) – Photo by Hillary https://www.flickr.com/photos/lamenta3/4334144802
Photo Five (Embroidery of Common Cold Virus) – https://www.flickr.com/photos/hey__paul/7714734358
Photo Six (Sneeze) – By James Gathany – CDC Public Health Image library ID 11162, Public Domain, https://commons.wikimedia.org/w/index.php?curid=6701700
Photo Seven (Cost of the common cold) – By http://wwwihm.nlm.nih.gov/ihm/images/A/27/712.jpg, Public Domain, https://commons.wikimedia.org/w/index.php?curid=21321786
Photo Eight(Shark poster) – By WPA artist “G S Jr” – Via http://www.loc.gov/pictures/item/98516749/, Public Domain, https://commons.wikimedia.org/w/index.php?curid=7894761
All blog content copyright Vivienne Palmer. Free to use and share non-commercially, but please attribute and link back to the blog, thank you!