Definition

Rat-bite fever refers to an infection which develops
after having been bitten or scratched by an infected animal.

Description

Rat-bite fever occurs most often among laboratory
workers who handle lab rats in their jobs, and among
people who live in poor conditions, with rodent infestation.

Children are particularly likely to be bitten by
rodents infesting their home, and are therefore most likely
to contract rat-bite fever. Other animals that can carry
the types of bacteria responsible for this illness include
mice, squirrels, weasels, dogs, and cats. One of the
causative bacteria can cause the same illness if it is
ingested, for example in unpasteurized milk.

Causes and symptoms

There are two variations of rat-bite fever, caused by
two different organisms. In the United States, the bacteria
Streptobacillus moniliformis is the most common cause
(causing streptobacillary rat-bite fever). In other countries,
especially Africa, Spirillum minus causes a different
form of the infection (called spirillary rat-bite fever).

Streptobacillary rat-bite fever occurs up to 22 days
after the initial bite or scratch. The patient becomes ill
with fever, chills, nausea and vomiting, headache, and
pain in the back and joints. A rash made up of tiny pink
bumps develops, covering the palms of the hands and the
soles of the feet. Without treatment, the patient is at risk
of developing serious infections of the lining of the heart
(endocarditis), the sac containing the heart (pericarditis),
the coverings of the brain and spinal cord (meningitis),
or lungs (pneumonia). Any tissue or organ throughout
the body may develop a pocket of infection and pus,
called an abscess.

Spirillary rat-bite fever occurs some time after the
initial injury has already healed, up to about 28 days after
the bite or scratch. Although the wound had appeared
completely healed, it suddenly grows red and swollen
again. The patient develops a fever. Lymph nodes in the
area become swollen and tender, and the patient suffers
from fever, chills, and headache. The skin in the area of
the original wound sloughs off. Although rash is less
common than with streptobacillary rat-bite fever, there
may be a lightly rosy, itchy rash all over the body. Joint
and muscle pain rarely occur. If left untreated, the fever
usually subsides, only to return again in repeated two- to
four-day cycles. This can go on for up to a year,
although, even without treatment, the illness usually
resolves within four to eight weeks.

Diagnosis

In streptobacillary rat-bite fever, found in the United
States, diagnosis can be made by taking a sample of blood
can be cultured, to allow the growth of organisms. Examination
under a microscope will then allow identification
of the bacteria Streptobacillus moniliformis.

In spirillary rat-bite fever, diagnosis can be made by
examining blood or a sample of tissue from the wound
for evidence of Spirillum minus.

Treatment

Shots of procaine penicillin G or penicillin V by
mouth are effective against both streptobacillary and
spirillary rat-bite fever. When a patient is allergic to the
penicillins, erythromycin may be given by mouth for
streptobacillary infection, or tetracycline by mouth for
spirillary infection.

Prognosis

With treatment, prognosis is excellent for both types
of rat-bite fever. Without treatment, the spirillary form
usually resolves on its own, although it may take up to a
year to do so.

The streptobacillary form, found in the United
States, however, can progress to cause extremely serious,
potentially fatal complications. In fact, before antibiotics
were available to treat the infection, streptobacillary
rat-bite fever frequently resulted in death.

Prevention

Prevention involves avoiding contact with those animals
capable of passing on the causative organisms. This
can be an unfortunately difficult task for people whose
economic situations do not allow them to move out of
rat-infested buildings. Because streptobacillary rat-bite
fever can occur after drinking contaminated milk or

or fluid from a painful joint. In a laboratory, the sample
water, only pasteurized milk, and water from safe
sources, should be ingested.