Re: Avian Flu and "The Black Death" of the Middle Ages

Here is a copy from "The Merck Manual" - an
encyclopaedia of current medical practice.


PLAGUE (Bubonic Plague; Pestis; Black Death)



An acute, severe infection appearing most commonly
in a bubonic or pneumonic form, caused by the
bacillus Yersinia pestis.



*Aetiology and Epidemiology



Yersiniapestis (formerlyPasteurellapestis) is a
short bacillus that often shows bipolar staining
(especially with Giemsa stain) and may resemble
safety pins.

Plague occurs primarily in wild rodents (eg, rats,
mice, squirrels, prairie dogs); it may
be acute, subacute, or chronic, and urban (mainly
murine) or sylvatic. Massive human epidemics have
occurred (eg, the Black Death of the Middle Ages);
more recently, plague has occurred sporadically or
in limited outbreaks. In the USA, > 90 % of human
plague occurs in the south-western states,
especially New Mexico, Arizona, California, and
Colorado. Bubonic plague is the most common form.



Plague is transmitted from rodent to humans by the
bite of an infected flea vector. Human-to-human
transmission occurs by inhaling droplet nuclei
through the cough of patients with bubonic or
septicemic plague who have pulmonary lesions
(primary pneumonic plague). In endemic areas in
the USA, a number of cases have been associated
with household pets, especially cats. Transmission
from cats can be by bite, or, if the cat has
pneumonic plague, by inhalation of infected
droplets.



*Symptoms and Signs



In bubonic plague, the incubation period is
usually 2 to 5 days but varies from a few hours to
12 days. Onset is abrupt and often associated with
chills; the temperature rises to 39.5 to 41° C
(103 to 106° F). The pulse may be rapid and
thready; hypotension may occur. Enlarged lymph
nodes (buboes) appear with or shortly before the
fever. The femoral or inguinal lymph nodes are
most commonly involved (50%), followed by axillary
(22%), cervical (10%), or multiple (13%) nodes.
Typically, the nodes are extremely tender and
firm, surrounded by considerable oedema; they may
suppurate in the 2nd wk. The overlying skin is
smooth and reddened but often not warm. A primary
cutaneous lesion, varying from a small vesicle
with slight local lymphangitis to an eschar,
occasionally appears at the bite. The patient may
be restless, delirious, confused, and
uncoordinated. The liver and spleen may be
palpable. The-WBC count is usually 10,000 to
20,000/p.L with a predominance of immature and
mature neutrophils. The nodes may suppurate in the
2nd wk.



Primary pneumonic plague has a 2- to 3day
incubation period, followed by abrupt onset of
high fever, chills, tachycardia, and headache,
often severe. Cough, not prominent initially,
develops within 20 to 24 h; sputum is mucoid at
first, rapidly shows blood specks, and then
becomes uniformly pink or bright red (resembling
raspberry syrup) and foamy. Tachypnea and dyspnea
are present, but pleurisy is not. Signs of
consolidation are rare, and rales may be absent.
Chest x-rays show a rapidly progressing pneumonia.



Septicemic plague usually occurs with the bubonic
form as an acute, fulminant illness. Abdominal
pain, presumably due to mesenteric
lymphadenopathy, occurs in 40% of patients.
Pharyngeal plague and plague meningitis are less
common forms. Pestis minor, a benign form of
bubonic plague, usually occurs only in endemic
areas. Lymphadenitis, fever, headache, and
prostration subside within a week.



*Diagnosis and Prognosis



Diagnosis is based on recovery of the organism,
which may be cultured from blood, sputum, or lymph
node aspirate. Because surgical drainage may
disseminate the organism, needle aspiration of a
bubo is preferred. Y. pestis can grow on ordinary
culture media or be isolated by animal (especially
guinea pig) inoculation. Serologic tests include
complement fixation, passive hemagglutination, and
immunofluorescent staining of a node or tissue
biopsy or secretions. Prior vaccination does not
exclude plague in the differential diagnosis,
since clinical illness may occur in vaccinated
persons.
The mortality rate for untreated patients with
bubonic plague is about 60%, with most deaths
occurring from sepsis in 3 to 5 days. Most
untreated patients with pneumonic plague die
within 48 h of symptom onset. Septicemic plague
may be fatal before bubonic or pulmonary
manifestations predominate.



*Prophylaxis and Treatment

Rodents should be controlled and repellents used
to minimize fleabites. Although immunization with
standard killed plague vaccine gives protection,
vaccination is not indicated for most travellers
to
countries reporting cases of plague. Travellers
should consider prophylaxis with tetracycline 500
mg po q 6 h during exposure periods.

Immediate treatment reduces mortality to < 5%. In
septicemic or pneumonic plague, treatment must
begin within 24 h with streptomycin 30 mg/kg/day
IM in 4 divided doses q 6 h for 7 to 10 days. Many
physicians give higher initial dosages, up to 0.5
g IM q 3 h for

48 h. Tetracycline 30 mg/kg IV or po in 4 divided
doses is an alternative. Gentarrticit, is probably
also effective, although no controlled clinical
trials have been conducted. For plague meningitis,
chloramphenicol should be given in a loading dose
of 25 mg/ kg IV, followed by 50 mg/kg/day in 4
divided doses IV or po. A multidrug-resistant
strain has been reported from Madagascar.

Routine aseptic precautions are adequate for
patients with bubonic plague. Those with primary
or secondary pneumonic plague require strict
(airborne agent) isolation. All pneumonic plague
contacts should be under medical surveillance;
their temperatures should be taken q 4 h for 6
days. If this is not possible, tetracycline 1
g/day po for 6 days can be given; however, this
can produce drug-resistant strains.




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