Bubonic Plague

Any scientific reason why the bubonic plague like the one that swept Europe and GB and even made it to Arabia in 546 AD, wouldn’t have just wiped out the human race conpletely? Or were some people just immune to it?

Some people were immune, some people got sick and recovered. Not everybody died, it just seemed that way to the survivors. Any disease organism, which is a kind of parasite if you think about it, that kills ALL of its hosts won’t last very long in the evolutionary scheme of things.

Surely not. I know this was the Dark Ages in Europe, but how dumb were they? :wink:

BTW the fact that plague has not (it is still around) wiped everyone out it not due to plague’s cunning and foresight, it is just luck. If the disease wiped everyone and thus itself out, that would just be tough luck for the plague.


A little off topic but…

I had watched a Discovery Channel program on Nostradamus. Since I had never really been particularily interested in him, knew little or nothing of his life. Very interesting to hear that he was physician who was relatively successful at treating patients during the Black Death. He practiced cleanliness, and used pills that he made out of rose hips to treat the sick. (Rose hips are evidently high in vitamin c.) Not to ironic either that people became suspicious of him during this time because whenever he came to town to treat the sick many people got better. Must have been a bitch to be brilliant back in those days. Damned if you do and damned if you don’t. He’s a doctor, he makes people well and it’s suspected that he’s a witch. Oh well, not too much unlike anyone now that might have a new idea. (Luckily you only get crucified in the media. Instead of at the stake.)


Ooh…my first post on this message board. Like a good message board user, I lurked for quite awhile before jumping in. However, my inexplicable fascination with the Plague (a twist on “train wreck syndrome” perhaps?) compels me to add what I know to this discussion.

The causative agent of bubonic plague is a fun little bacteria called “Yersinia pestis”. Actually, there are three forms of plague, of which bubonic is only the most common/well-known as well the first to strike an area. Y. pestis also causes pneumonic and septicemic plague. Bubonic plague is caused by infection in the lymph nodes, has a mortality rate of roughly 75% and runs its course (to whatever end) in 2-3 weeks; pneumonic is related to infection of the lungs, is upwards of 90% fatal if untreated, and runs for less than a week; and septicemic plague means direct infection of the blood, is almost invariably fatal, and will kill in about 24 hours (which doesn’t leave much time for treatment). All three forms of the disease swept through Europe in the mid-14th century and several times thereafter. Bubonic is actually the least virulent form of the plague but is almost always the first form to appear.

As to why everyone didn’t die, it is because (as was noted by other posters) some people survived the bubonic form AND some people (notably the Jewish population) practiced good hygiene…of course, these people were also sometimes slaughtered by frightened neighbors who reasoned that if you didn’t get the disease you must be the cause of it.

Plague is still around today; it is now endemic to all coastal areas, and in the US can be found not only on the coasts but in fleas infecting the squirrels in the woods in inland areas in the West (“sylvatic plague”; New Mexico/Arizona have the US’s highest incidence of plague). However, it is susceptible to antibiotics (tetracycline and erythromycin, NOT penicillin) and is therefore treatable. Fatalities in the US occur usually because physicians don’t know to look for the disease and misdiagnose. In addition to antibiotics, increased hygiene in the US and Western Europe has definitively decreased the impact of plague. However, plague outbreaks still occur in areas of high population density in the third world. In the mid-90s, I recall hearing about an outbreak of pneumonic plague in one of the poorer parts of India; however, I think there was some confusion about that since usually the pneumonic and septicemic forms do not appear until after bubonic plague.

A number of reasons.

(1) After a certain mortality level is reached, there are less “vectors” (i.e., warm-blooded animals and people) to carry the disease.
(2) Some people are immune or resistant to the plague. They lived while the others died.
(3) Once the plague broke out in an area, people would tend to avoid going there. Eventually reasons #1 and #2 would allow the plague to die out.

As to the comment of Medieval people thinking everyone was dead, that’s not too surprising. I’ve read that some historians estimate the death toll to be as high as 1 in 3. In some cases, whole families and even towns were literally wiped out.

I read once in a collection of historical accounts of the plague in the mid 1300’s that it seemed to be remarkably selective in it’s mortality rate. I read of towns where the rate was less than 5%, and towns in Northern Tuscany and what would now be Eastern Hungary where the rate was nearly 100%. One book I read (I think it was A Distant Mirror by Tuchman) gave a report by a Irish monk who was the sole survivor of his monastery, which was located on an island. He believed for several years that everyone in the world had died, and he was the last one left, until he saw a fishing boat one day.

I also read reports of entire cities in Germany abandoned, with wolves roaming through the town feasting. Just imagine what today’s world would be like if swept by a disease with “only” a 10% mortality rate.

Saw a great PBS show last week (Secrets of the Dead or some such) that posited that the 6th century outbreak of the plague was due to a huge eruption, probably of Krakatoa. (Also linked said eruption to the downfall of the Roman/Byzantine empire, the Avar empire, the Teotehuacan (I think) empire, and rise of Islam, FWIW.)

According to the biology dude they had on, the bacillus is only transmitted from fleas to animals if the temp is below a certain level (25 degrees, IIRC). The climate change from the eruption was sufficient to drop mean temperatures long enough for a plague epidemic. Seems that if the temp is higher, the bacilli just pass through the flea normally, but at lower temps they clog up flea guts and cause the flea to regurgitate bacilli into animal hosts. Or something like that.

Anyhoo, t’was very interesting.

The plague was originally spread by fleas carried by black rats. The more rats, the more fleas, and when the rats died of the plague, the fleas moved to human hosts easily. There is speculation that the “little ice age” of the 1300s made the plague worse because the climate was cooler and wetter - perfect for fleas to propagate.

Because of the superstitious nature of medieval culture, people often burned or killed off cats as instruments of the devil - destroying one of the few predators that could have helped keep the rat numbers down.

Here’s an account of the plague from Agnoli de Tura of Siena:

The movement of the plague - from Asia to India, to the Middle East, to the Mediterranean, to Europe, to Russia - outlined the geography of medieval trade routes. The plague reached Cyprus in the summer of 1347, and took another four years to reach Russia. In the course of four years, one of every three people in Europe died.

45 - 75% of Florence died in a year.

60% of Venice died in 18 months. 500 - 600 a day during the peak.

As mentioned previously, immunity and cleanliness were two reasons that many survived the plagues. Another was isolation. Transportation systems were primitive, and most europeans lived and died in an area no larger than they could walk in a day. Survival rates were much higher in rural areas because people had less opportunity to come in contact with the bacteria, and because their living conditions were a bit more sanitary.

On a side note, the poster who suggested that it was in the bacteria’s own interest to leave some people alive was correct. From an evolutionary standpoint, a disease that kills its victims too quickly, such as ebola, is not going to do very well. If it’s host dies without having an opportunity to spread the bacteria, the organism cannot propagate. Conversely, a virus such as AIDS is not considered highly evolved because it is too difficult to transmit. The “best” viruses and bacteria are easily transmissible and allow their hosts to live long enough to infect as many people as possible. To this end, the common cold is considered one of the most advanced viruses known today. (Regular mutations have also allowed the rhinovirus to survive the era of modern medicine, another triumph for this seemingly insignificant bug) :slight_smile:

As a matter of reference, I know the first part because I studied medieval history for a few years in university. The second part I know because I lived with a biology student and we were both fascinated by virology. :slight_smile:


First, a nitpick. AIDS the the disease, the virus is HIV.

Second: HIV is difficult to transmit? Tell that to sub-Saharan Africa. Sexually transmitted diseases are quite succesful, actually. Plus, the fact that HIV consistently evades the immune system without immediately killing the host would indicate to me that it is highly evolved. But it’s not really useful to classify viruses as “more” or “less” evolved.

I think a better way to say it is that it is often not in the best interest of the bacteria to infect humans, as they are often “dead-ends” in the infection cycle.

Actually, rhinoviruses are very simple as far as viruses go. Much simpler than HIV, in fact. Also, around 150 viruses are associated with the common cold. So the cold that you got last winter probably isn’t the same one you’ll get next Christmas. Therefore, just because the common cold is common doesn’t mean that the viruses that cause it are “advanced”.

I haven’t seen that episode yet, but Britannica says “The only known eruption [of Krakatoa] prior to 1883 occurred in 1680.”

This thread, The evolution of blood discusses how people with certain blood types may be more resistant to the plague. This might explain the wide variation in death rates from one area to another. I am the one who originally brought this up in that thread, but it’s only now that I realize the 2 sources I used seem to disagree about which blood type(s) benefit.

I did catch the Secrets of the Dead series, pop over to http://www.pbs.org then go to the History section to find the link. Anyhow after seeing the program, which is basically an overview of David Keys’ book ‘Catastrophe’, you find he makes a good point. It doesn’t seem to have convinced the entire scientific community of the relationship between the eruption and chaos the world over but he definitely puts forth some good arguments.
Just as an aside the episode they did on the Hindenburg was quite good as well. They put forth the theory that the major cause of the fire was that the fabric was painted with what amounted to rocket fuel. I was going to pop it into the thread that we had going some months back about this very subject but I forgot.

If you want mortality rate go for smallpox.

Any of you all read “Biohazard” by Ken Alibeck yet? He’s also done a lot of interviews. He used to head up the USSR bioweapon program, even after it was supposedly done away with in '72. The Soviets successfully crossed smallpox with Ebola and made it usable as a weapon. As far as we know, they still have it ready for distribution.

But the point about smallpox is relevant to the plague discussion. As long as a disease is around at low levels or is in some other way able to cause host populations to develop immunity, the disease and the hosts live in a sort of balance. Sometimes the balance teeters one way or the other as in Europe in the 1340’s and 50’s. It’s only lately that we’ve been able to teeter it in our favor with various drugs and vaccines. But as someone once said, in the long run the long run always wins. Since the time we thought we made smallpox extinct, we as a population have lost essentially all of our immunity to it. If —or when— it comes back from either a bioweapons lab or some rainforest, the world population may well be affected the way the American Indians were when smallpox hit them.

This also applies to a lesser degree (I hope) to polio: back when the country and world were dirtier (especially when horese were everywhere and crapped all over) we had but usually didn’t recognize abortive polio as a fairly common childhood disease:

Polio, abortive: A minor form of infection with the polio virus, abortive polio accounts for 80 to 90 percent of clinically apparent cases in the US, chiefly occurring in young children. The usual symptoms emerge three to five days after exposure to the virus, and include slight fever, malaise, headache, sore throat, and vomiting. Full recovery occurs in 24 to 72 hours. It does not involve the nervous system or permanent disabilities of any kind.

Public sanitation and the decline of horse-drawn vehicles made this much more rare. Then we had polio epidemics and the rush to get a vaccine. Now we see that childhood immunization rates are falling, and so we prepare ourselves via inaction for the next epidemic.

I can’t think of a single instance where a disease of any kind has completely wiped out a species. Is anyone aware of any species which has been driven to extinction by disease?

The closest example I can think of is maybe Dutch Elm Disease, but even that didn’t wipe out all elm trees.

I wouldn’t want to have the hubris to say that it could never happen, but I have my doubts. I think we have enough genetic diversity that at least some of the population will be either resistant or immune to any disease that comes along.

For example, aren’t there people walking around now who have had long-term HIV infections without apparent ill effect? (Correct me if I’m wrong on this one.)

Sorry, but this sentence really amuses me. Think about it for a minute:

Bob: Hey, everyone’s dead.

Bill: Well, you’re not. And I’m not.

Bob: That’s because we’re survivors. Survivors don’t die.

Bill: Then everyone’s not dead, Bob.

Bob: Sure seems like it to me, Bill.

The fundamental reason is pretty basic: viruses that kill off their hosts too quickly don’t get a chance to spread. Viruses that are too lethal simply die out, because the hosts die before they can infect others.

Lots of people (like the guy that wrote THE HOT ZONE) assume that high death rate = effective virus. But of course viruses don’t “care” about whether their host dies. The only thing important for the virus over the long haul is whether it’s able to spread to new hosts. That means that a really successful virus doesn’t kill its host, or even seriously impair it. The host has many more chances to spread the virus if it’s alive.

From that point of view, the cold viruses are the really successful viruses in humans. The highly lethal viruses like plague are gaudy failures. (In humans, that is. The plague virus does much better in its “proper” host, the flea.)

Whoops, rereading my post I see kinda forgot to mention my main point…

It’s the speed that’s important. A virus that kills really quickly will “burn out” and stop spreading. For example, consider a virus that killed the host the instant it infected it. Such a virus will probably never get a chance to spread at all!

Bubonic plague killed too fast to have real chance of driving humanity to extinction in the Middle Ages.

In the long run, yes, a virus doesn’t want to off its prey, but considering that the blind-eye of evolution may create a strain that could kill and spread very quickly before the normal checks and balances take over.

Its hypothetical, but a virus that is airborne, highly contagious and kills relativly quickly (how long it takes to kill isn’t as important as how fast it can replicate and spread) could off an entire species.

Buy hey, the chances of that happening are probably slim. Err, if we ignore that most governments are busily trying to perfect a virus exactly like this. Go team!

Lets not ignore that a virus doesn’t have to kill everyone to remove the species, I’d like to see how well humans would fare if a majority of the population took off.

“What do you mean you can’t get the microwave to work!”