Common cold has troubled mankind for centuries and mankind has put forth various reasons for the cause and has tried out various remedies to fight it off. Today we know that it is caused by a virus; Human rhinovirus (HRV). They are remarkable simple with only 10 genes (we have about 20,000 genes) and yet they enter our body, outwit our immune system and give us cold. HRV spreads by making noses run. People with colds wipe their noses, get the virus on their hands and then spread the virus onto door knobs and other surface they touch. The virus hitches onto the skin of other people who touch those surfaces and then slips into their body. Over the next few hours, by trickery, they slip into the cells that line the interior of nose, throat and lungs they then use these host cells to make copies of its genetic material and protein shells to hold them. The host cells then rip apart and the new virus escapes. HRV infect relatively few cells and cause little harm. So why do they cause such miserable experience? Blame our immune system. Infected cells release special signalling molecules, called cytokines, which attract nearby immune cells, which then make us feel awful. These immune cells create inflammation around affected area, which triggers a scratchy feeling and leads to production of a lot of mucus. So even after the virus has escaped, we have to wait for our immune system to calm down, before we can say that our cold is finally over.
There is no vaccine for cold, nor any drug that has consistently shown signs of killing the virus. Infact, some treatment for cold may be worse than the disease itself. Parents often give their children cough syrup for cold, despite the fact that it does not help. Cough syrup itself poses a wide variety of rare yet serious side effects, like convulsions, rapid heart rate and even death. Another popular treatment is antibiotics, despite the fact that they only work on bacteria and are useless against viruses.
HRV comes in many genetic variants; any drug that attacks one protein on the virus may prove useless against another variant. Every time you have a cold, it is very much possible that you have been affected by a new variant, since the body has built immune resistance to the previous strains.
Do we need a cure for common cold? HRV itself is relatively mild and most colds are over in a week. In fact HRV may offer some benefits to their human hosts. Many studies show that children who get sick with relatively harmless viruses and bacteria may be protected from immune disorders when they get older, such as allergies and Crohn’s disease. HRV may also train our immune system not to over react to minor triggers, instead directing their assaults to real threats. Perhaps we should not think of colds as ancient enemies but as wise old tutors.
Condensed from ‘A planet of viruses’ by Carl Zimmer.