Read condition-specific symptoms and clinical context for Yersinia pestis. The plague bacterium: a rodent-and-flea organism that still causes a few thousand human cases a decade, mostly in three countries.
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 describes bubonic plague as the most common form, with an incubation period of 1 to 7 days; PHAC gives 2 to 10 days and CDC gives an incubation period of 2 to 8 days.
Possible symptoms: Fever; Headache; Chills; Weakness; One or more swollen, painful lymph nodes (buboes).
WHO gives an untreated case-fatality ratio of 30 to 60% for bubonic plague and states that antibiotic therapy is effective when administered promptly. Plague is a notifiable disease; suspected cases need urgent clinical and public-health action.
CDC describes septicemic plague as occurring within days of exposure, either as a primary infection or from untreated bubonic plague. PHAC gives 100% untreated fatality for this form.
Possible symptoms: Fever; Chills; Extreme weakness; Abdominal pain; Shock; Bleeding into the skin and other organs.
PHAC gives 100% untreated fatality for septicaemic plague. It can follow untreated bubonic plague or arise directly, so it is not a separate disease so much as a further stage or route.
WHO describes pneumonic plague as the most virulent form, with incubation as short as 24 hours; PHAC gives 1 to 3 days. It is the only form that spreads readily between people.
Possible symptoms: Fever; Headache; Weakness; Rapidly developing pneumonia with shortness of breath; Chest pain; Cough, sometimes with bloody or watery mucus.
WHO states that pneumonic plague is invariably fatal unless treated early, with high recovery rates when treatment begins within 24 hours of symptom onset. Suspected pneumonic plague requires immediate isolation and treatment decisions by clinicians and public-health authorities.
Living in or travelling to a plague-endemic area, or being bitten by fleas, does not mean plague follows.
The bundled sources give no symptom list for exposure that does not lead to illness, and none is invented here. PHAC records that transmission is most commonly through the bite of infected rodent fleas, particularly Xenopsylla cheopis, with more than 200 species and subspecies of rodents acting as hosts, so most of the organism’s life happens outside people. WHO notes that human-to-human transmission occurs primarily through pneumonic plague via respiratory droplets and that bubonic transmission between humans is rare. This profile assigns no human carriage state.
Exposure assessment and any preventive treatment are decisions for clinicians and public-health authorities in the affected area. This app gives no exposure advice.
Source check: 2026-09-20. Educational content; independent scientific review remains pending.