---
name: Plague
slug: plague
type: biological_process
status: legacy
version: 4.2.1
released: "~1346 CE (major release); earlier builds date to antiquity"
maintainer: Yersinia pestis (primary); various [zoonotic spillover](/zoonotic-spillover) contributors
dependencies:
  - fleas
  - rodent populations
  - dense human settlement
  - inadequate sanitation
  - trade routes
license: Public Domain (unfortunately)
tags:
  - disease
  - mortality
  - history
  - microbiology
  - catastrophe
  - biblical
---

Plague

What it actually is

A bacterial infection that found an extremely efficient distribution model and used it.

How it works

Yersinia pestis colonizes the gut of a flea. The flea bites a rodent. The rodent eventually runs out of viable hosts. The flea, hungry and indiscriminate, bites a human. The bacterium enters the lymphatic system and begins building infrastructure it was never invited to build.

Three main deployment modes:

Variant	Entry Point	Mortality (untreated)
Bubonic	Flea bite, lymph nodes	~30-60%
Septicemic	Bloodstream direct	~90-100%
Pneumonic	Airborne droplets	~100%

Pneumonic is the prestige edition. It removed the flea as a dependency entirely.

Features

Rapid scaling across populations with no configuration required
Self-propagating under most medieval infrastructure conditions
Produces visible, dramatic symptoms (buboes, blackened extremities) that function as a kind of aggressive error logging
Capable of reshaping labor markets, feudalism, and theological certainty in a single release cycle
Historically triggered significant advances in medicine, public health, and quarantine theory as patches

Known bugs

Occasionally kills the host too quickly to propagate effectively, which is a design conflict the pathogen has never fully resolved
The flea vector is sensitive to climate, creating inconsistent regional rollouts
Modern antibiotics (doxycycline, streptomycin) represent a near-complete patch. The v4 build has not successfully responded to this

Changelog

v1.0   ~3000 BCE   First documented outbreak, Egypt/Middle East
v2.0   541 CE      Plague of Justinian. Destabilized the Byzantine Empire
v3.0   1346 CE     Black Death. Killed ~30-60% of Europe. Major release
v3.1   1665 CE     Great Plague of London. Considered a minor patch by this point
v4.0   1855 CE     Third Pandemic, origin: Yunnan province
v4.2   1994 CE     Surat, India outbreak. Brief pneumonic cluster, contained
v4.2.1 present     Sporadic cases. ~1000-3000 per year globally. Status: legacy

Error codes

BUBO_FAILURE        Lymph node swelling exceeds containment. Sepsis imminent.
HOST_EXHAUSTED      Population density insufficient for continued spread.
VECTOR_ABSENT       No flea or rodent reservoir detected. Transmission stalled.
ANTIBIOTIC_INTERRUPT Treatment initiated. Process terminating.
THEOLOGICAL_PANIC   Social cohesion collapsing. See: [flagellant movements](/flagellant-movements)

Edge cases

Plague still circulates in the American Southwest among prairie dog colonies. The landscape looks peaceful. It is not.
Survivors of the Black Death contributed to a genetic variant (CCR5-delta32) that also confers partial resistance to HIV. History caching old solutions for future problems.
Quarantine as a concept was literally invented for this. The word comes from the Italian for "forty days." Someone counted.

FAQ

Is it gone? No. It is resting.

Could it happen again at scale? The dependencies (dense cities, global trade routes, antibiotic resistance trends) are mostly still installed.

What stopped it historically? Rats built immunity. Fleas followed. Humans got lucky and called it civilization.

drafting spec…