– is caused by the bacterium Yersinis pestis. Plague remains a major infection in many tropical countries.
The reservoir for the bacillus in urban infection lies in the black rat (Rattus rattus), and less importantly the brown (sewer) rat (Rattus norvegicus). It is conveyed to humans by the rat ?ea, usually Xenopsylla cheopis: Y. pestis multiplies in the gastrointestinal tract of the ?ea, which may remain infectious for up to six weeks. In the pneumonic form (see below), human-to-human transmission can occur by droplet infection. Many lower mammals (apart from the rat) can also act as a reservoir in sylvatic transmission which remains a major problem in the US (mostly in the south-western States); ground-squirrels, rock-squirrels, prairie dogs, bobcats, chipmunks, etc. can be a?ected.
Clinically, symptoms usually begin 2–8 days after infection; disease begins with fever, headache, lassitude, and aching limbs. In over two-thirds of patients, enlarged glands (buboes) appear – usually in the groin, but also in the axillae and cervical neck; this constitutes bubonic plague. Haemorrhages may be present beneath the skin causing gangrenous patches and occasionally ulcers; these lesions led to the epithet ‘Black Death’. In a favourable case, fever abates after about a week, and the buboes discharge foul-smelling pus. In a rapidly fatal form (septicaemic plague), haematogenous transmission produces mortality in a high percentage of cases. Pneumonic plague is associated with pneumonic consolidation (person-to-person transmission) and death often ensues on the fourth or ?fth day. (The nursery rhyme ‘Ringo-ring o’ roses, a pocketful o’ posies, atishoo! atishoo!, we all fall down’ is considered to have originated in the 17th century and refers to this form of the disease.) In addition, meningitic and pharyngeal forms of the disease can occur; these are unusual. Diagnosis consists of demonstration of the causative organism.
Treatment is with tetracycline or doxycycline; a range of other antibiotics is also e?ective. Plague remains (together with CHOLERA and YELLOW FEVER) a quarantinable disease. Contacts should be disinfected with insecticide powder; clothes, skins, soft merchandise, etc. which have been in contact with the infection can remain infectious for several months; suspect items should be destroyed or disinfected with an insecticide. Ships must be carefully checked for presence of rats; the rationale of anchoring a distance from the quay prevents access of vermin. (See also EPIDEMIC; PANDEMIC; NOTIFIABLE DISEASES.)... Medical Dictionary