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Rat-bite fever (RBF)
is an uncommon disease known for its endemicity to occur worldwide.
Although most patients tend to develop mild symptoms with improvement
from conventional antibiotics, it can progress with severe
complications with a mortality rate as high as 13% without proper
treatment.
This is a
systemic infection that afflicts people in areas where rat control is
lacking.
Rat-bite
fever (RBF) takes two forms :
(i) Rat-bite
fever by Streptobacillus moniliformis is also known as Haverhill
fever.
(ii) The
second form of RBF, named Sodoku by the Japanese because of its high
incidence in that country, is caused by the bacteria Spirillum
minus (Spirillum minor).
Causative
organisms:
There are two
distinct organisms and hence two diseases.
(i) One
of the agent is a spirochete, Spirillum minus (Spirillum minor)
, 0.15 micrometer wide and 2 to 5 micrometer long, with one to six
spirals.
(ii) The
second cause is streptobacillum moniliformis , a gram negative
bacillus, 0.1 to 0.7 micrometer wide and 1 to 5 micrometer long
, which appears as clusters of organisms in tissue , forming long wavy
chains or filaments.
Mode of
infection:
Human
infection can result from a bite or scratch from an infected or
colonized rat, handling of an infected rat, or ingestion of food or
water contaminated with infected rat excreta.
Clinical
presentation:
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Rat-bite fever
caused by S. moniliformis has an incubation period ranging from 1 to
22 days. Disease is characterized by flu-like symptoms including
irregularly relapsing fever accompanied by chills, vomiting and
headaches, and asymmetric polyarthritis generally affecting the large
joints. This is followed by a maculopapular rash on the
extremities, palms and soles.
Most cases
resolve with treatment but if left untreated result in fatality in 13%
of the cases.
Complications
of rat bite fever include
bacterial endocarditis ,
myocarditis, and
pericarditis, and abscesses in the brain or other tissues, tenosynovitis. Other complications include regional lymphadenopthy,
anemia, meningitis, pneumonia, and myalgia.
[In a fatal
case of Streptobacillus moniliformis in an infant the autopsy
findings included an interstitial pneumonia , fibrinous endocarditis ,
mild mononuclear meningitis , hepatosplenomegaly and lymphadenopathy ,
erythrophagocytosis , and sinusoidal mononuclear cell infiltrates in
regional lymph nodes and the liver.]
Sodoku is
characterized by a recurrent fever. A roseolar-urticarial rash
sometimes develops. Arthritis is rare. There is regional lymphadenitis
and lymphangitis with accompanying flu-like symptoms including
malaise , headaches, and enlargement of the lymph nodes adjacent to
the wound.
The diagnosis
of streptobacillary rat-bite fever is made after isolation of
Gram-negative bacilli from a blood-culture and from cutaneous lesions.
Finally identification of the organism is confirmed by molecular
biology analysis.
Physicians
should consider RBF as a possible diagnosis when fever, rash, and
exposure to rats are part of the patient's history.
Zoonotic
infections may present a significant hazard to persons with
occupational or recreational exposure to rats.
Education on
hazards of animal contact and other preventive measures are essential
to prevent this disease.
Penicillin is
effective in S. minor infection.
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