In the world I'm envisioning, an individual has been accidently sent to a sort of alternate history version of the world, one that is at roughly feudal level of tech/culture, but with the nations divided up differently than in our history. The Traveler didn't plan for this transition and thus didn't have time to prepare for it.

After arriving, he earned some interest from the king of a nation (impressing the king with the laptop the Traveler carried before the battery inevitably died) and promised to try to help improve the nation with his future knowlege, but his inability to produce any quick & obvious feats with his knowledge leaves the traveler with limited support from the king.

Around this time, another neighboring nation has a major disease start to spread, and it looks like it could become a full blown epidemic. Both his king and the neighboring king are worried, and so the Traveler's king asks the traveler to use his future knowledge to fix the disease (the Traveler had sold himself especially on his promise to help with lowering disease via use of sanitation techniques).

The Traveler is very knowledgeable about evolution & genetics, providing him some tangental knowledge about disease beyond basic high school biology, but he is not a doctor or deeply trained in handling of disease. His first attempt to help is sending basic 'best practices' he is aware of for working with disease, like quarintene, sanitation, use of face masks, and boiled water. He also sends a rather long 'questionare' to the foreign king which he asks the king to send to numerous city healers which asks a number of questions about frequency of disease, traits common to those infected, and targeted questions trying to determine what method of spreading the disease may use. The answers he eventually get back point to one commonality: areas with stagnant water or which otherwise would be prone to high number of mosquitoes have far higher rates of infection. His questions targeting other potential plague vectors haven't shown any other likely plague vectors.

So having a theory as to how the disease is spread, it's time to send advice on how to get rid of the plague vector. The questions I have are twofold. What kind of advice (other then the obvious “mosquitoes are bad” and “try to avoid stagnant water”) can he give to combat the mosquitoes’ spreading of the disease? How significant an impact can this and the earlier basic sanitation advice have in stopping the spread of the disease? Keep in mind that he hasn't yet proven himself to the foreign king and thus the king is not yet confident how much money/effort he is willing to commit to following through on the advice of a stranger.

If the Traveler's advice does help, how obvious to the kings will it be that the advice was the cause of the disease loosing momentum?

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    $\begingroup$ Is this to assume we're ignoring the diseases he has brought back in time with him ? as in the future human body housing evolved bacteria that would likely kill people from several centuries ago? $\endgroup$ Sep 19, 2018 at 13:24
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    $\begingroup$ @BladeWraith yes, because I don't think that's as dangerous as you believe. With our modern medicine and sanitation we mostly stop diseases before they reach us rather then trusting our body to learn to combat them. This means any bacteria/disease in our bodies are likely 'minor' ones, not anything that is likely to kill, because anything more dangerous we would have already treated with antibiotics. Unlike when the America's were colonized we aren't all walking around with very lethal diseases that we can survive having only because we let those without immunity die from them already. $\endgroup$
    – dsollen
    Sep 19, 2018 at 13:29
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    $\begingroup$ The rather impotent bacteria that our bodies cope with without any serious health issues could very well kill someone that hasn't inherited the natural antibodies that evolution has provided, this is why Native Americas where several depleted by disease after the arrival of Europeans, they hadn't grown up exposed to it. and Antibiotics can't cure the Common Cold or the flu which most humans carry a small amount of in their systems and these very easily could kill, in fact even today they still do $\endgroup$ Sep 19, 2018 at 13:38
  • $\begingroup$ @BladeWraith I understand your point, but I still feel like it's not the same situation. Still I'm not confident enough of my own medical knowledge to say for certain. So I've posted a separate question regarding your point to allow other's to weigh in on how large a threat it is: worldbuilding.stackexchange.com/questions/125522/… $\endgroup$
    – dsollen
    Sep 19, 2018 at 14:01
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    $\begingroup$ I would just like to point out that "He also sends a rather long 'questionare'" would very difficult in a medieval setting because of the scarcity of paper. $\endgroup$ Sep 20, 2018 at 3:37

4 Answers 4


Mosquito borne diseases aren't (usually) epidemic

They are endemic. When there is a carrier as prevalent as mosquitos, then every time there are lots of mosquitos around (i.e. all year in the wet tropics, wet season in the wet-dry tropics, summer in the sub-tropics) then the disease spreads.

Diseases like malaria and dengue don't suddenly spread all over the world, because their vector (the mosquito) does not spread that rapidly. Mosquitos are small and don't travel fast or far. Instead, these diseases rage seasonally, or year round in their set locations. Malaria ravaged the poor and unhealthy of Rome every summer as mosquitos bred in the swamps; same with Georgia in the US. Dengue is a danger all year in the Congo or Liberia.

Occasionally a mosquito borne epidemic will move to a previously un-occupied region; this primarily happened during the long distance voyages of the Age of Exploration. But this is the exception rather than the rule. Because endemic mosquito born diseases stay in one place, the local population tends to have a higher resistance. Death toll is low and steady during each infectious season.

By comparision, fast-spreading and hard-hitting epidemics have different mechanisms for spreading. The worst epidemics are dominated by plague, influenza, smallpox, and cholera. Plague is spread by fleas via rats. Fleas don't travel long distances, but rats do. Influenza is airborne and transmitted by coughing and sneezing. Smallpox is spread through bodily fluids; usually tiny airborne droplets of mucus. Cholera is waterborne and spreads via the fecal-oral route: drinking poopy water. These four are the plagues that killed hundreds or thousands a day in historical big cities.

To 'answer' the question

Mosquito borne diseases are the hardest to stop, which is why you see them around to this day. Malaria is now the most deadly disease in the world, while smallpox and plague are extinct and nearly-extinct, respectively. You would be better off using a non-mosquito vector in any case to make your time traveller more effective.

Killing rats is no easy task, nor is getting rid of fleas. But for the air and water contact diseases, strict quarantines are more or less effective. Doctors or nurses seeing patients need to wear gloves, cover their face, and wash with soap afterwards. No one else should be allowed to see the infected until recovery or death. After recovery or death, you can burn the person's bed sheets, or just lock the house and wait a week. Oh, and for cholera, make sure people stop pooping in the river.

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    $\begingroup$ +1 for "poopy water". (Or maybe because the answer is very good, your choice.) $\endgroup$ Sep 19, 2018 at 13:33
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    $\begingroup$ This doesn’t directly answer the question. The question says to assume a mosquito plague is epidemic. Useful info, but not an answer. Nothing herein addresses stopping mosquitoes. $\endgroup$
    – SRM
    Sep 19, 2018 at 13:36
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    $\begingroup$ darn it. I was worried committing to a specific disease vector would lead to someone telling me that vector was a stupid choice ;). I was originally going to do plague, but I thought it was easier for him to identify disease spread via mosquito then one spread via flea. I'm going to toy with this being a new mosquito disease that they fear will become epidemic for now; without their realizing it won't spread further; but if I don't get good answers that will allow the travelers to have the sort of obvious life saving advice I want I'll look back to considering flea's as vector instead. $\endgroup$
    – dsollen
    Sep 19, 2018 at 13:38
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    $\begingroup$ @dsollen I updated with some tips for making it more realistic. The real problem is that mosquito borne diseases are really hard to stop, too. $\endgroup$
    – kingledion
    Sep 19, 2018 at 13:48
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    $\begingroup$ That is a fair answer, and means I'll likely have to target a different vector. I'm actually shying away from water based disease precisely because it's a little too easy to treat, I'm not sure I want to make things quite that easy for my protagonist. I'll let this question sit for a little while longer in case someone else offers any useful insights, but there is a decent chance I may end up posting a separate question about a Plague and how to treat it in the future. Though, again I'm not certain how easy it is for his questionnaire to 'prove' that the disease is spread via rat. $\endgroup$
    – dsollen
    Sep 19, 2018 at 14:05

Fight mosquito borne disease like they did in turn of the century Panama.

The measures taken to combat mosquito-borne disease during the construction of the Panama canal were low tech and effective. They are within reach of a medieval society.


The most ambitious part of the sanitation program, though, was undoubtedly the effort to eradicate the mosquitoes Aedes aegypti and Anopheles, the carriers of yellow fever and malaria, respectively, from the canal zone...

Gorgas divided Panama into 11 districts, and Colón, Panama, into four. In each district, inspectors searched houses and buildings for mosquito larvae. If larvae were found, carpenters were dispatched to the building, and work was done to eliminate objects or places where stagnant water could collect...

Gorgas organized a major program to drain and fill swamps and wetlands around the Canal Zone. Many miles of ditches were dug, and grass and brush were cut back over wide areas. Oiling was used in a variety of means: workers with spray tanks were sent to spray oil on standing pools, and smaller streams were tackled by placing a dripping oil can over the waterway, which created a film of oil over each still patch of water in the stream.

Gorgas also took another step in his efforts to eradicate mosquitoes in Panama: fumigation. He fumigated the residences of Panamanians who had been confirmed to have contracted yellow fever. "Pans of sulfur or pyrethrum were then placed in the rooms, the right quantity of powder was weighed out (two pounds per thousand cubic feet), and the pans were sprinkled with wood-alcohol and set alight" (Cameron 132). When the effectiveness of this procedure was realized, fumigation was extended to all of Panama. Within a year of Stevens's appointment, every building in Panama had been fumigated, using up the entire US supply of sulfur and pyrethrum. In 1906, only one case of yellow fever was reported, and until the end of the Panama Canal's construction, there were zero.

It is pretty awesome low tech public health.

1: Use the presence of larvae as an indicator for standing water and take measures to eliminate this water, treat it with oil, or improve flow such that it is no longer stagnant.

2: Fumigate houses with sulfur and pyrethrum. Pyrethrum is present in certain plants and you could make a smoky fire with these plants and sulfur.

Also these measures would make sense in the context of an Aristoltelian mindset - "malaria" means bad air. The working arms of this endeavor could keep this mindset and just consider the larvae as indicators of circumstances which produce bad air. The fumigation kills adult mosqitoes in buildings but could also be considered as a purification of contaminated air.

  • $\begingroup$ Not sure the oiling could be done with medieval tech, but yes the rest is quite possible. $\endgroup$
    – T.E.D.
    Sep 20, 2018 at 11:33
  • $\begingroup$ @T.E.D - they could press oil from grains / seeds / fruits but that is throwing out a lot of food value. They could use crude oil which was known and used as tar. $\endgroup$
    – Willk
    Sep 20, 2018 at 13:30

Don't go gettin' all sciencey.

Ancient Romans battled malaria (Italian for Bad Air) successfully under surprisingly similar conditions. They did so without fully understanding the mechanics behind the parasite but by simply observing as you did.

As someone who often has to explain technology to people who grasp it as much as your medieval ruler, my best advice is not to get all confusing. Make simple comparisons, simple tests (even if they're fixed! as long as they are understandable and believable, it can go a long way to sell the core message), and a simple message. And ALWAYS appeal to the person's intelligence and make it clear it was their idea...

For instance:

"King, as you have assuredly noticed and pointed out on many occasions, your subjects living near bodies of stagnant water have contracted serious illnesses which others living far away have not. There is bad air at work here your Lord."

Then tell him how it's in his best interests. Losing a few peasants, ehhhh.... not a big deal...

"Having this evil on your kingdom is a plague of the worst kind. In fact, your hunting camp has bodies of stagnant water which could possibly breed this bad air. The last thing I would want to see is you or your nobles contracting this plague."

Tell him how he can gain.

"And your neighbors who are currently suffering have not an idea on what is causing this plague. How they would look up to you if you were able to cure them! Or not, and let them weaken and take over their lands. You can battle this threat!" By lowering the cost of entry, you become more palatable as a solution. It's not an outright lie (you can later claim you miscalculated due to shovel technology), but you're just trying to get a Yes from him. Once the project is halfway done, most people can see the end more clearly.

Again, don't get sciencey, but something along the lines of:

"Throughout history this bad air has been an issue. I would like to help your kingdom not become one of those victims. Simply by draining the swamps, you not only gain more arable land to tax, but you put an immediate stop to this problem. I estimate (insert something at half the cost in time or people here) days could be expended to solve this issue."

As for your last question, it is easy to confuse correlation and causation. You can attempt to use this to your advantage as much as the king may try to use it against you. If the neighbor still suffers the plague, and you don't any longer, bring up that the only change has been your swamp draining. If you help the neighbor at the king's bidding, you can even add an extra data point.

Edit: If the king still doesn't go for it, offer to show how some simple techniques such as mosquito nets (Cleopatria even may have used one or saps of some trees can lessen infection rates.


He could try out things in a small trial area first . Areas where Kings trusted healers look after.

In addition to sanitation techniques , he could recommend other things like mosquito nets.

He can show improvements by showing that the trial areas show less increase of sick people compared to other.This vetted by the healers.


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