1. IDENTIFICATION
(Click
for APHA Plague manual, 2000).
A specific
zoonosis involving rodents and their fleas, which transfer the
bacterial infection to various animals and to people. Initial signs and
symptoms may be nonspecific with fever, chills, malaise,
myalgia (muscular pain or tenderness), nausea,
prostration, sore throat and headache. Commonly a lymphadenitis develops
in those lymph nodes that drain the site of the flea bite, where there may
be an initial lesion. This is bubonic plague, and it occurs more often in
lymph nodes in the inguinal area (90%) (see
figure) and less commonly in those in the
axillary and cervical areas. The involved nodes become swollen, inflamed and
tender and may suppurate. Fever is usually present. All forms, including
instances in which lymphadenopathy is not apparent, may progress to
septicemic plague with bloodstream dissemination to diverse parts of the
body, that include the meninges. Endotoxic shock and disseminated
intravascular coagulation (DIC) may occur without localizing signs of infection.
Secondary involvement of the lungs results in pneumonia; mediastinitis or
pleural effusion may develop. Secondary pneumonic plague is of special
significance, since respiratory droplets may serve as the source of person
to person transfer with resultant primary pneumonic or pharyngeal
plague; this can lead to localized outbreaks or devastating epidemics. Though
naturally acquired plague usually presents as bubonic plague, purposeful
aerosol dissemination as a result of biowarfare or a
terrorist
event would be manifest primarily as pneumonic plague.
Untreated bubonic plague has a case-fatality rate of about 50%-60%. Plague organisms have been recovered from throat cultures of asymptomatic contacts of pneumonic plague patients. Untreated primary septicemic plague and pneumonic plague are invariably fatal. Modem therapy markedly reduces fatality from bubonic plague; pneumonic and septicemic plague also respond if recognized and treated early. However, patients who do not receive adequate therapy for primary pneumonic plague within 18 hours after onset of respiratory symptoms are not likely to survive.
Visualization of
characteristic bipolar staining, "safety pin" ovoid,
gram-negative organisms in
direct microscopic examination of material aspirated from a bubo, sputum
or CSF (cerebral-spinal fluid) is suggestive, but not conclusive,
evidence of plague infection (see
figure).
Examination by FA test or antigen capture ELISA is more specific and is
particularly useful in sporadic cases. Diagnosis is confirmed by culture and
identification of the causal organism from exudate aspirated from
buboes (inflamed and swollen lymph node),
from blood, CSF or sputum, or by a fourfold or greater rise or
fall in antibody titer. Slow growth of the organism at normal incubation
temperatures may lead to misidentification by automated systems. The passive
hemagglutination test (PHA) using Yersinia pestis
Fraction-1 antigen is
most frequently used for serodiagnosis. Medical personnel should be aware of
areas where the disease is endemic and entertain the diagnosis of
plague early; unfortunately, plague is often misdiagnosed, especially in
travelers who develop illness after returning from an endemic area.