The plague bacterium: a rodent-and-flea organism that still causes a few thousand human cases a decade, mostly in three countries. Explore its illustrative 3D model, human context, and sources.
PHAC describes Y. pestis as a Gram-negative coccobacillus 1 to 3 micrometres in length, ovoid in shape, with characteristic bipolar staining giving a safety-pin appearance; it is non-motile, does not form spores, and grows optimally at 29 to 30 degrees Celsius while surviving from 4 to 40 degrees Celsius. PHAC records 4,547 reported plague cases worldwide from 21 countries between 2010 and 2019, with 94% of reported cases in either the Democratic Republic of the Congo or Madagascar; WHO names the Democratic Republic of the Congo, Madagascar and Peru as the three most endemic countries. Transmission is most commonly through the bite of infected rodent fleas, with pneumonic plague additionally spreading by respiratory droplets.
WHO gives an untreated case-fatality ratio of 30 to 60% for bubonic plague and describes untreated pneumonic plague as invariably fatal, with pneumonic plague able to kill within 18 to 24 hours of onset. PHAC gives 100% untreated fatality for the septicaemic and pneumonic forms. WHO also states that high recovery rates follow treatment started within 24 hours of symptom onset, so these figures describe untreated illness rather than an inevitable outcome.
Yersinia pestis · One ovoid coccobacillus. Bipolar staining is a preparation effect, not a pair of organelles; the conditional F1 coat is omitted. This is a species-informed teaching diagram; colours, proportions, envelope spacing and internal detail are illustrative. The model uses muted illustrative colours; stains, colony pigments and microscopy colourization are not natural cell colours. Anatomy is enlarged for phone viewing. Morphology reference: Yersinia pestis · pathogen safety data sheet.
Source check: 2026-09-20. Educational content; independent scientific review remains pending.