Plague did not disappear when the great historical pandemics ended. The bacterium Yersinia pestis continues to circulate between wild mammals and fleas in areas known as natural foci. Human infection is now uncommon, but it can occur wherever infected animals, flea vectors and people come into contact.
Three geographies that should not be confused
A natural focus is an ecological system in which the bacterium can persist. It does not mean that people throughout the area are currently exposed. A reported human case is a person counted under a surveillance definition. An outbreak event is a cluster or increase that public-health authorities investigate and describe in a particular place and period.
These layers answer different questions. Combining them into one case map creates a false impression that every ecological area is an active outbreak.
Where recent cases are reported
WHO reporting for 2019–2025 shows that most reported human cases were concentrated in the Democratic Republic of the Congo and Madagascar. Smaller numbers were reported by several other countries. A country with no case in a table may still contain recognized natural foci, and missing reporting cannot safely be interpreted as zero disease.
In the United States, plague became established in wild rodent populations after arriving in port cities around 1900. Modern human cases occur mainly in rural areas of the West, particularly parts of New Mexico, Arizona and Colorado.
How Plague Map represents this
Human events and natural foci use separate layers. Event coordinates are approximate public-report locations, not patient addresses or exposure boundaries. Core case totals include only reviewed human records; ecological layers do not add to those totals.