Rat bite fevers
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Rat Bite FeversDr.T.V.Rao MD
Rat-bite Fever (RBF)Rat-bite fever (RBF) is an infectious disease that
can be caused by two different bacteria.
Streptobacillary RBF is caused by Streptobacillus
moniliformis in North America while spirillary RBF
or sodoku is caused by Spirillum minus and
occurs mostly in Asia. People usually get the
disease from infected rodents or consumption of
contaminated food or water..
If not treated, RBF can be a serious or even
fatal disease.
Rat-bite feverRat-bite fever is an
acute, febrile human
illness caused by
bacteria transmitted by
rodents, rats or mice in
most cases, which is
passed from rodent to
human via the rodent's
urine or mucous
secretions.
Risk FactorsAny person who is exposed
to the bacteria that cause
RBF is at risk for getting the
disease. Some people who
may be at increased risk
include those who:
Live in rat-infested buildings
Have pet rats at their home
Work with rats in
laboratories or pet stores
Infected Rodents Spread
the Disease
.It is a rare
disease spread
by infected
rodents and can
be caused by two
specific types of
bacteria.
Spirillum MinusShort Gram negative spiral organism3 – 5 microns
Stains with Giemsa stain
Dark field microscope useful
Not cultured- Can be isolated by inoculating the specimen Intraperitoneally into Mic
Geographic location of Rat
bite fevers
Most cases occur in Japan, but specific
strains of the disease are present in the
United States, Europe, Australia, and
Africa. Some cases are diagnosed after
patients were exposed to the urine or
bodily secretions of an infected animal.
Dr.T.V.Rao MD 8
Signs and Symptoms
Symptoms do not manifest for two to four weeks after exposure to the organism, and the wound through which it entered exhibits slow healing and marked inflammation. The fever lasts longer and is recurring, for months in some cases. Rectal pain and gastrointestinal symptoms are less severe or are absent. Penicillin is the most common treatment.
Streptobacillus
moniliformis
Symptoms depend on the
bacteria that caused the
infection. Symptoms due to
Streptobacillus
moniliformis may include:
Chills
Fever Joint pain, redness,
or swelling Rash
Spirillum minus
Symptoms due to Spirillum minus may include: Chills
Fever
Open sore at the site of the bite
Rash -- may be red/purple plaques
Swollen lymph nodes near the bite
Streptobacillosis
The Streptobacillosis form of rat-bite fever is known by the alternative names Haverhill Fever and epidemic arthritic erythema. It is a severe disease caused by Streptobacillus moniliformis, transmitted either by rat bite or ingestion of contaminated products (Haverhill fever).
Dr.T.V.Rao MD 12
Streptobacillosis
After an incubation period of 2–10 days,
Haverhill fever begins with high prostrating
fevers, rigors (shivering), headache and
polyarthralgia (joint pain). Soon an exanthem
(widespread rash) appears, either
maculopapular (flat red with bumps) or
petechial (red or purple spots) and arthritis of
large joints can be seen. The organism can
be cultivated in blood or articular fluid.
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Transmission
S. moniliformis and S. minus are part of the normal respiratory flora of rodents. Either organism may be transmitted to humans through bites or scratches. Infection can also result from handling an infected rodent (even with no reported bite or scratch), or ingestion of food or drink contaminated with these bacteria (Haverhill fever). Rats are considered the natural reservoir of RBF, but the bacterium has also been found in other rodent species such as, mice and gerbils. Person-to-person transmission has not been reported.
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Pathogenesis
S.minus enters the body through rat urine
Incubation period 1-4 weeks
Clinically present with swelling of lymph nodes near the site of bite with relapsing fever and skin rash
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Severe illnesses can
include:
Infections involving the heart (endocarditis, myocarditis, or pericarditis)
Infections involving the brain (meningitis)
Infections involving the lungs (pneumonia)
Abscesses in internal organs
While death from RBF is rare, it can occur if it goes untreated.
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DiagnosisThis condition is
diagnosed by
detecting the
bacteria in skin,
blood, joint fluid,
or lymph nodes.
Blood antibody
tests may also be
used.
Other Methods of
Diagnosis To diagnose
streptobacillary rat bite
fever, blood or joint fluid
is extracted and the
organisms living in it are
cultured. Diagnosis for
spirillary rat bite fever is
by direct visualization or
culture of spirillum from
blood smears or tissue
from lesions or lymph
nodes.
Prevention
Whilst obviously preventable by staying away from rodents, otherwise hands and face should be washed after contact and any scratches both cleaned and antiseptics applied. Prompt cleaning of wounds with antiseptic solution, and reducing the risk of rat bites. The effect of chemoprophylaxis following rodent bites or scratches on RBF is unknown. No vaccines are available for these diseases. Improve conditions to minimize rodent contact with humans is the best preventative measure for RBF.
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Avoid Contact with Rats
Improve conditions
to minimize rodent
contact with humans
is the best
preventative
measure for RBF.
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PreventionAnimal handlers, laboratory workers, sanitation and sewer workers must take special precautions against exposure. Wild rodents, dead or alive, should not be touched and pets must not be allowed to ingest rodents. Those living in the inner cities where overcrowding and poor sanitation cause rodent problems are at risk for RBF. Half of all cases reported are children under 12 living in these conditions.
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Treatment
Responds to penicillin
antibiotics or where
allergic to this
erythromycin or
tetracycline's for
respectively
streptobacillary or
spirillary infections.
Programme Created by Dr.T.V.Rao
MD for Medical and Paramedical
students in the Developing world