Plague

Definition

An acute, often fatal zoonotic disease caused by the bacterium Yersinia pestis, transmitted primarily by flea vectors (especially Xenopsylla cheopis and other rodent-associated fleas) and maintained in enzootic cycles among wild rodents and their ectoparasites. In humans, bubonic plague presents with swollen lymph nodes; pneumonic and septicemic forms may follow. The term also denotes any severe epidemic disease in historical usage, but in entomological and epidemiological contexts refers specifically to this flea-borne bacterial infection.

Etymology

Middle English plage, from Late Latin plaga 'stroke, wound', from Latin plaga 'blow, affliction', from plangere 'to strike, lament'

Example

Xenopsylla cheopis, the Oriental rat flea, becomes infective after feeding on a septicemic rodent; Yersinia pestis multiplies in the flea's proventriculus, eventually blocking it so that regurgitated bacteria are transmitted to new hosts during subsequent blood meals.

Synonyms

• Bubonic plague
• Black Death (historical)

Related Terms

• Vector
• Xenopsylla
• Yersinia pestis
• flea
• Epizootic
• enzootic
• Proventriculus
• sylvatic plague
• urban plague

Usage Notes

Distinguish 'plague' (the specific Yersinia pestis disease) from general epidemic disease. Sylvatic plague refers to the wild rodent-flea cycle; urban plague involves commensal rats and their fleas. Plague is a classic example of vector-borne transmission where the arthropod vector's biology—specifically proventricular blockage—directly determines transmission efficiency. The term should not be used loosely for any insect-borne disease.