Avoiding Ninja Cholera

On the off-chance the OP or anyone else sees this, I'm actually working on reverse engineering this game (thanks, quarantine) and can answer this for certain.

In the oregonii.dat file, every health problem has a flag determining whether it's possible to die instantly, and a separate variable for the chance of that happening if you get that problem (i.e., if you do contract the illness/get injured, do you get the normal set of choices, or do you just die?)

Those diseases and chances are:

• Accidental gunshot, 20%
• Animal bite, 10%
• Animal mauling, 10%
• Cholera, 20%
• Drowning, 25%
• Freezing, 10%
• Internal injuries, 20%
• Snakebite, 5%

If you die instantly, the death screen has a custom message. If you go into the oregonii.eng file, in the list of strings ("____ has cholera," etc.) for any given disease, it's the last one. (Incidentally, there are a couple of these messages that are definitely customized but seem unused, so maybe at one point there were other things you could die instantly from?)

As for how to avoid it, unless there's some other factor I haven't found -- medical skills don't seem to matter for this specific roll -- all you can do is edit the .dat in a hex editor. (Which means you can also do stuff like make a bad cold instantly fatal 100% of the time.)

We played this game so much as kids. (And it still runs on Windows 10, apparently.)

One very overlooked feature of this game is the immense amount of detail of the in-game Guidebook. There is a wealth of historical and geographical information in this almost-200-page document (although most of the Guide is quite useless to gamers who only want quick info).

Nestled inside here are a number of hints about the game play. There are tips for keeping morale high, and for preventing problems. Most diseases and their associated remedies are also listed.

Regarding ninja cholera, the best resource that I could find was a magazine article from one of the developers or the first edition of The Oregon Trail (You Have Died of Dysentery: Exploring The Oregon Trail’s Design History). They wanted a game with a very high degree of replayability. From the article:

[T]he simulation is driven by a set of mathematical formulas tied to state variables. Each state variable tracks the current value of some important quantity.

. . .

Instead of a single simulation model, I designed the following interlocking models, each consisting of several to many interlocking mathematical formulas:

• Climate and weather
• Health
• Progress on the trail
• Supplies (cash, food, oxen, bullets, clothing, and spare parts)
• River crossings
• Scoring system

. . .

My new design included an ongoing health model for the entire party, along with tracking individual illnesses and injuries. The weather, food rations, and pace all have cumulative effects on the party’s health, which can improve or decline over time.

Due to the interlocking nature of events, depending on the mathematical model and the game's random deviation for a particular event, health can drop to zero immediately.

You cited cholera as being the more notorious. In our experience, it was hunting accidents, especially during hunting trips where a bullet was shot that did not hit any game. Often after exiting hunting, we would be greeted with a screen that said we had suffered a gunshot wound, and occasionally we simply died immediately. Even though the Guidebook claimed that having a sheath for our shotgun or rifle would reduce the chances of such injuries, we did not notice much difference in practice.

Of course, we got around the whole problem by saving often.