How an infection becomes an epidemic

After every disaster – man-made or natural – the news gets flooded with warnings about an eminent epidemic of infectious diseases, like for instance cholera. And in all fairness, it is indeed a serious risk. But how does that work?

Many infectious diseases are transmitted from person to person. Either directly by normal contact, sexual intercourse (in both a normal and abnormal way) or blood contact, or indirectly via a mosquito for instance. And this is completely different from all the other causes of illness.

For example:

  • I can’t get diabetes because I had unprotected sex with someone with diabetes whom I just met in a bar after too many Jägerbombs (don’t judge me)
  • The passengers in the bus can’t get kidney stones because someone sits too close to them, it’s just annoying if someone gets in your personal space

To get an infectious disease most of the time you have to actively do or actively not do something. In theory it should be easy to not get infected.

Actively do: if I have unprotected sex I am prone to get infected with all kinds of nasty stuff, so I should have made him wear a condom (I know, easier said than done, but still very effective).

Actively not do: if I stick the needle from someone else in my arm, I am bound to be infected with that person’s blood infections like HIV or hepatitis B (I … have … to … resist …)

Actively do and actively not do: if I don’t wash my hands (so please do) after I touch someone with diarrhea (please don’t, no really don’t), I am likely to infect myself and the persons I get in contact with afterwards.

Sounds simple to protect yourself, doesn’t it? Here’s the catch: in practice it is not always that easy and sometimes nearly impossible. Because what if you can’t get condoms? What if you need an immediate blood transfusion? Or if you don’t have fresh and safe water you can drink and wash your hands with? Let’s use this last example to make it clearer.

Lack of sanitation and fresh water is like throwing a big party for all infectious diseases to come and pick people to infect. You are reading this, so you probably have internet access and thus, most likely, access to clean water from a tap or other resources close by.

But don’t get too comfortable, if a hurricane occurs that destroys your supply, that flushes away your toilet and breaks open your sewer system letting all human waste flood the streets, you too will be in big trouble.

Cholera is one of the many diseases and always present in nature. With good hygiene, clean water, and a good health system it is not a big problem. But without it, cholera is the party animal. It starts with infecting just one or two people. They will soon get the typical heavy diarrhea that’s like pooping rice water all day long (not that I have any experience with it). They will dehydrate and they will die without care.

Unfortunately, this is not the end, cholera is just getting started.

Where is the diarrhea going when the sewer system to flush with it no longer exists? What happens with the buckets that are used to catch the diarrhea? How do you wash your hands after you’ve picked up that bucket? And what about the small children that have no idea what basic hygiene entails? That’s exactly what cholera likes. Easy access to a lot of people that basically have nowhere to hide. It will go from 1 person to 3, to 9, to 27 and so on and so on. Until an entire group that’s living closely together is infected, for instance in the emergency camp that has just been founded after a hurricane.

So, an epidemic is just moments away for all of us if we don’t have basic hygiene and knowledge of the infectious agents. And after a natural disaster it is hard to stay healthy and all the right support needs to be provided as fast as possible.

In all other cases, think about what you can actively do and actively should not do. Go wash your hands, use clean needles and please, don’t kiss a dead person when you don’t know what he or she died of (if not convinced, more about why not to do this will follow soon).

Do this and you’ll probably be fine, … for now.


Picture: Refugee camp for Rwandans in Kimbumba, eastern Zaire (current Democratic Republic of the Congo), following the Rwandan genocide.This image is a work of the Centers for Disease Control and Prevention, part of the United States Department of Health and Human Services, taken or made as part of an employee’s official duties. As a work of the U.S. federal government, the image is in the public domain.

Smallpox and the start of vaccinations

“Good old days”?! Not if you talk about infectious diseases. Being an infectious disease specialist before the last century would have been a dramatically frustrating profession. Even the simplest of infections could not be effectively treated.

“Good old days”?! Not if you talk about infectious diseases. Being an infectious disease specialist before the last century would have been a dramatically frustrating profession. Even the simplest of infections could not be effectively treated.

In the 16th century there was an impressing global epidemic of smallpox, which is caused by the variola virus. This disease had been causing problems on and of for quite some time already and never failed to cause multiple deaths among the infected patients. The Inca population in South America was hit pretty bad in those days, the mortality among these people was 60-90%, and this was at the same time that the Spanish conquistadors were attacking them. So perhaps we could say that almost the entire continent of South America speaks Spanish not due to those Spanish horsemen, but in fact as a result of the variola virus.

The difficult situation with the smallpox is that the symptoms are very vague, some muscle aches, fatigue and fever. In this first stage of the disease patients are actually really contagious, so not recognizing the symptoms in time results in major problems and spread of the virus. After about 2 weeks the patient can get the classic skin leasions.

The only thing that the people in the 16th century could do to try to decrease the severity of the disease was a so called “inoculation with variola” (variolation). This meant that an attenuated virus was put on the skin in the hope that your body would start an immune response without actually killing you. In the work up for this “treatment”, children would be starved and about a liter of blood taken from them (don’t ask me why). After the variolation, the child would be locked in a barn until the disease had subsided or the child had died. Congrats for the ones that survived, I hope they had some good psychiatrists to regain their trust in humanity…

On a beautiful day in 1798 (don’t really know if it was, just sounds nicer), an English doctor called Edward Jenner was fed up with this torture of children. He too had undergone the variolation “treatment” and probably never got over the horror (again, total speculation). There had to be another way!

He noticed that the milkmaids of that time appeared to be immune to the smallpox. He thought that this might be due to the fact that they had probably been exposed to the, not so sickening, cow-pox. He decided to test this theory. He found a “volunteer” named James Phipps -the 8 years old son of his gardner- and injected him with the pus he had scraped from a cow-pock blister from a milkmaid. I mean, that just sounds like a brilliant idea, doesn’t it? Anyway, after some time he tried to infect the child with variola using the old “variolation” method but our little James didn’t get sick.

I can’t say that this was the most ethical way of investigating, but it was effective and had huge consequences for the world as we know it. Dr Jenner has written everything down in his book “An inquiry into the causes and effects of the Variolae vaccinae; a disease discovered in some of the Western Counties of England, particularly Gloucestershire, and known by the name of the cow pox”. Which is, like the title suggests, a real briefly written page turner…

From that day forward the procedure to prevent small pox would be to infect somebody with the cow-pox virus called “inoculation with vaccinia”, later “vaccination” after the word vacca that means cow in Latin. This particular vaccination could be terminated in 1980 when, thanks to intensive effort of the WHO, small pox was eradicated. OK, truth be told, it’s still present in 2 laboratories in Russia and the USA so maybe we should continue to take good care of our cows, just to be sure…