by Debbie “The Rat Lady” Ducommun
Updated
Rat-bite
fever (RBF) is the common name for two similar diseases caused by different
bacteria. The most common form is
caused by Streptobacillus moniliformis, a
gram negative rod-shaped bacteria.
This is also called Streptobacillary
fever. The less common cause of
rat-bite fever is Spirillum minus, sometimes called Spirillum minor, a gram negative spiral-shaped
bacteria. This is also called Sodoku, a name that comes from
The most
common way for people to contract rat-bite fever is by being bitten or
scratched by either a wild or domestic rat, or being scratched by an item
exposed to rats, such as a cage.
Occasional cases have been reported among children who live in wild
rat-infested homes, but who had no direct rat contact. The disease can also be contracted from
mice, squirrels, gerbils, and animals who eat wild rodents, including dogs and
cats.
The Strep form of the disease can also be contracted from ingesting
food or liquid contaminated by rat feces or urine. In fact, when the strep
form of the disease includes nausea, abdominal pain, and/or vomiting and a sore
throat, it is called
There was a
case in 1998 in
Both
bacteria that cause the disease in humans can be carried in the mouth of rats
without causing disease. The
occurrence of Streptobacillus moniliformis
in healthy laboratory rats ranges from 10% to 100% depending on the
population. In wild rats the
occurrence ranges from 50% to 100%.
There are no statistics of the occurrence of the bacteria in pet
rats. Since so many pet rats are
treated with antibiotics, I would think the occurrence of the bacteria might be
very low.
A tragic
case of rat-bite fever occurred in
The
statement on the website is actually “It has been estimated that 10% of
rat bites result in some form of RBF.” I also found the same statement repeated
on other websites.
I believe the
original resource for this statement is a study published by someone named
Richter in 1946. (I was not able to
find the actual study, but only a summary of it.) This study reported on the incidence of
rat bites and rat-bite fever in inner city Baltimore from 1939-1943 and
concluded that during this time, in an area of less than 2 square miles, at
least 93 people were bitten by rats.
Obviously these bites would have been from wild rats, not pet rats. Sixty-five of the people with rat bites
were treated in the hospital and of these, 7 developed rat bite fever. None of them died.
So, if this
is the origin of the statement that “10% of rat bites result in rat-bite
fever” it has been taken out of context. The correct conclusion from this study
is that 50 years ago, 10% of urban people who went to the hospital after being
bitten by a wild rat developed symptoms of rat-bite fever. I’m sure the incidence of the
disease among people bitten by pet rats is much lower. Another factor is that the symptoms of
rat-bite fever are similar to those of other diseases, especially Rocky
Mountain Spotted fever, coxsackie B virus and meningoccemia, and it’s difficult to diagnose, so
it’s possible that some cases reported to be rat-bite fever were
something else.
Richter’s
study found that 60% of those bitten were under one year of age, so it is
likely that young children are more susceptible to the disease. Of the 6 cases I know of that have
occurred up through 1998 that were probably from pet rats, 5 of them were in
children, including a 5-year-old, a 4-year-old and a 2-year-old.
I contacted
the Center for Disease Control to ask them about the incidence of rat-bite
fever and they told me that it isn’t a reportable disease, so there are
no statistics on it. They only
receive a few calls about it each year from health workers who want to know how
the disease is diagnosed.
Symptoms and Treatment
In the Strep form, if the disease is caused by a rat bite, the
bite usually heals up, although occasionally there may be swelling or infection
at or near the bite site. The
incubation period can range from 1 to 22 days, but onset usually occurs 2-10
days after exposure. The
first symptoms are usually like the flu including fever and chills, headache,
muscle aches, and weakness.
There may or may not be nausea, abdominal pain, vomiting and a sore
throat. Then, 2-4 days later a rash
of small red bumps usually forms on the hands and feet, mostly on the palms and
soles. However, the rash can also
occur on the arms, legs and trunk.
Arthritis in the knees and hips is also a very common symptom. Sometimes there is swelling in the lymph
nodes nearest the bite.
Here are
some websites with case studies showings photos of the rash on the hands and feet.
In one case, a 7-year-old boy had not just a rash on his hands, but blisters
and peeling skin.
http://www.cmaj.ca/content/175/4/354.full
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1797630/
http://jcp.bmj.com/content/58/11/1215.full
In most
cases, the disease goes away on its own within 2 weeks, but symptoms can
continue for several months and 13% of untreated cases are fatal. In rare cases the infection can cause
pneumonia and can travel to the heart and brain causing damage and
abscesses. In cases that are treated
promptly the disease is almost always cured without any residual effects.
The only way
to diagnose the Strep form for sure, either in humans
or rats, is to do a blood culture.
Because the bacteria is very difficult to grow, the culture must be done
in a very specific manner.
The Spirillus form has a longer incubation period, 4 to 28
days, and usually longer than 10 days. The initial wound may persist with
swelling and ulceration or may heal only to reappear at the onset of systemic
symptoms. The main symptom is a
cycle of fever lasting from 2 to 4 days. Malaise, headaches, and enlargement
of the lymph nodes adjacent to the wound are also common. Symptoms usually continue for 4 to 8
weeks but may continue for up to one year.
A rash of larger red wheals sometimes develops but is generally less
prominent than the rash produced by the Strep
form. Arthritis is rare. Complications may include infection of
the heart, meningitis, hepatitis, and enlarged spleen. If left untreated death results in 6% to
10% of the cases.
The Spirillus form cannot be cultured and must be diagnosed by finding
the bacteria itself in samples of blood, or in tissue or fluid from the lesions
or adjacent lymph nodes.
The
treatment for both types of the disease recommended by the Center for Disease Control
is intravenous penicillin for 5 to 7 days followed by oral penicillin for 7
days. For people allergic to penicillin, tetracycline or streptomycin can be
used. Other antibiotics such as
erythromycin, chloramphenicol, clindamycin and cephalosporins have been used
with some success in some cases.
To
summarize, rat-bite fever is a very rare disease that is easily treated if the
symptoms are recognized early enough.
Although I don’t know of any studies that show whether rats
treated with antibiotics can still carry the bacteria, it seems likely that
treating your rats with antibiotics will reduce the chance that they could pass
on the disease.
If you have
more questions, you can contact the Center for Disease Control at:
CDC Public Inquiries
(404) 639-3534
(800) 311-3435
http://www.cdc.gov/netinfo.htm
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