Where do Colds come from and What causes the Common Cold?

If we want to search for something good to come out of the 1918 disaster, perhaps we can find it in the spur to research in virology that it provoked.

In the 10 years after 1918, thousands of books and articles were published about the flu. One large problem posed by the flu virus is that it is so small.

Scientists in these years had no way of seeing it. They could see many microorganisms, of course, but all of them were the much larger bacteria that cause diseases associated with the flu, but not cause the flu itself. In addition, viruses, unlike bacteria, are very difficult to culture in a petri dish, they normally only live parasitically inside host cells.

On top of this, the flu virus is fussy about its host. The kinds that infect humans don’t often infect animals in the same way, and humans, for many and quite obvious reasons, make very poor experimental subjects. Despite all this, by the early 1930s several different viruses that cause the flu had been filtered out from the pool of microorganisms found in flu victims, and the viral nature of influenza was clearly established. In addition, the distinction between influenza and the relatively harmless cold was now becoming clear.

You are even more likely to get a cold than to get the flu, you and 62 million other Americans this year will get at least one. Most of you, 52.2 million, will be under 17 years old. There is no vaccine to prevent it; there is no medicine to cure it. This is not to say that people haven’t tried. In fact, there is a vast literature of cold cures, and some are honestly convinced that one or another of them works. It is not too cynical, however, to add that there are some who are willing to advertise and sell cures that they know full well are ineffectual.

Since colds are very common, and largely untreatable except symptomatically, there is an irresistible desire to cite just about anything as a cure, or at least a good treatment.

Onions, garlic, dill, wild indigo, cinnamon, teas and soups of all kinds, echinacea, hibiscus flowers, Peruvian balsam, marjoram, anise, spruce, peppermint, cardamon, purple cornflowers, if you can name it, it has been recommended by someone somewhere as the best thing to take if you have a cold.

Some of these remedies come with no promises or only very vague ones; others, like the ingestion of vast quantities of vitamin C, come decorated with scientific-sounding explications and endorsements from famous people. Undoubtedly, some of them will make some people feel better, but this is not the same thing as saying that they cure colds. Perhaps the best we could say of all these medicines is that they will work to cure colds about as well as anything else, which is to say they probably won’t work at all.

You can take them, and most of them (though perhaps not all) are harmless, but you’ll still get a cold, and you’ll still have to wait until it goes away. In the vast majority of cases, if you’re really careful; take vitamin C; use aspirin, saline nose spray, and other cold remedies; drink lots of liquids; and get plenty of rest, your cold will last about seven days. If you don’t, it will last about a week. Rarely, a cold can lead to complications, particularly bacterial infections that can cause sinusitis, bronchitis, and bacterial pneumonia, diseases that may require treatment with antibiotics. Colds themselves do not respond to antibiotics, which should never be used for that purpose.

Colds are caused by more than 200 different viruses, and about a third of them are rhinoviruses, nose viruses, in plain English, but of course cold (and flu) viruses specifically infect the lungs. The nose provides the most obvious symptoms, sneezing and dripping. Fever, headaches, and muscle aches are also common. Rhinoviruses, members of the genus Picornavirus, seldom cause serious illness.

Other cold viruses such as parainfluenza and respiratory syncytial virus cause mild disease in adults, but more severe illness in children. Another genus of viruses, the coronaviruses, probably also cause a large number of mild colds in adults, and other viruses can be involved as well. Between 10 and 15 percent of colds are caused by viruses that can also cause more serious illness, adenoviruses, Coxsackie viruses, influenza viruses, and others. But that still leaves about half of all colds for which no one knows the exact (presumably viral) cause.

Colds are usually a winter disease in the northern hemisphere. Although there is considerable controversy about exactly why certain diseases have seasonal patterns, there is no evidence that, say, going outside with wet hair on a cold winter day makes you any more susceptible to colds than if you’d dried your hair thoroughly before venturing out. Many diseases do have seasonal patterns, including flu, rotavirus, measles, and polio, among others, and the patterns are remarkably consistent from year to year.

Latitude correlates very closely with the patterns, the magnitude of seasonal peaks increases proportionately with distance from the Equator in either direction.

Since these seasonal cycles are so obvious and universal, and since no one has ever come up with a completely satisfactory reason why they happen, there are plenty of explanations offered by scientists and laypeople alike. A favorite layman’s explanation is that being cold gives you a cold, or, slightly more technically, being cold makes you more susceptible to the virus’s effect and reduces your resistance.

The problem is that no experiment designed to test this hypothesis, and there have been many of them, has ever proven any such causal connection. Some people feel that viruses migrate, that they travel back and forth to cooler (or in the case of certain viruses like polio, warmer) climates as the weather changes, or that they prefer rainy or dry weather and move with the seasons on that basis.

Correlations with the weather or temperature and the magnitude of a given pandemic can be made, but the problem is that the same virus that correlates with wet or warm weather in one place has an equally convincing correlation with dry or cold weather in another. Respiratory syncytial virus epidemics, for example, correlate with the cold months of winter in the United States, but in Hong Kong the same viral epidemics are closely correlated with the hotter months.

Some say it’s the seasonal behavior of the human host, crowded into small rooms in the winter, swimming in public swimming pools in the summer, for example, that causes the seasonal changes in infection rates. But this doesn’t explain why measles spreads in the winter in crowded rooms in England while failing to spread in the summer in crowded rooms at international conferences. Even the light/dark cycle and the corresponding pattern in the secretion of melatonin has been invoked as a possible explanation. There are plenty of guesses, but no one really knows for sure why there are winter and summer diseases.

Why you catch cold in the winter is still a mystery, but how you catch one is not. You catch it by having a virus get into your nose. You take a breath too close to someone who has just sneezed. More commonly, you shake hands with someone with a cold who has just scratched his nose and then you scratch your own nose, or you touch a door handle just touched by a cold sufferer and then put your hand near your face.

You don’t even have to touch your nose, rub your eye and tears from the eye drain through the nose, giving you a cold. One experiment showed the hand-to-hand transmission of colds to be extremely effective.

This study found that 11 of 15 hand-contact exposures of infected people with uninfected volunteers transmitted the illness. Then they tested how efficient this kind of transmission might be and found that the virus on infected volunteers’ hands was transmitted to recipients’ fingers during 20 of 28 ten-second hand contacts. That’s not a very long contact, and the distance from hand to nose, as we know, is quite short. The “hand-contact-followed-by-self-inoculation” route is very likely an important way in which the virus gets around.

The symptoms of a cold, the runny nose, the coughing, and the sneezing, are probably, like the symptoms of many other diseases, a reaction by the body’s immune system to attack by a foreign invader. White blood cells called to the site of infection by chemical signals from the virus infected cells give off a number of different chemicals to try to fight the infection. It is these chemicals that probably cause the swelling and inflammation of the nasal membranes and the leakage of fluid from capillaries and lymph vessels, with the resultant increased production of mucus. These chemicals are of great interest to researchers, who are trying to figure out whether drugs to block them might help alleviate cold symptoms.

There is a story here worth telling. The title of Alexander Fleming’s 1929 paper announcing his discovery of penicillin was “On the Antibacterial Actions of Cultures of a Penicillium, with Special Reference to Their Use in the Isolation of B. Influenzae.” Studying the organism that caused death from influenza was a major preoccupation of microbiologists at this time, and Fleming viewed penicillin as useful in that quest, that is, it could, in a petri dish, inhibit the growth of certain bacteria, making the organisms that it didn’t inhibit easier to find and study.

In other words, his chief hope for penicillin was that it could be used by researchers to eliminate the presence of various bacteria on a culture plate, leaving the organism thought to cause influenza unharmed. He referred to its possible use as an antibiotic in treating humans only briefly at the end of the paper.