What is rat-bite fever?

Definition

Rat-bite fever (RBF) is an infectious disease caused by two strains of
bacteria, Streptobacillus moniliformis
and Spirillum minus
. The bacteria are spread through the bite of rodents or through the
secretion of rodent fluids.

Causes

RBF primarily develops when rats bite or scratch humans, but infection can also occur simply by touching live or dead rats and by being exposed to secretions from their eyes, nose, or mouth. Additionally, cleaning rat cages and coming in contact with rat urine or feces can cause RBF. Living in rat-infested environments, such as impoverished areas, often leads to RBF, inadvertently ingesting food or water contaminated with rat feces or urine. Breathing in desiccated particles of rat feces may also result in RBF. Gerbils, squirrels, and weasels also carry RBF; furthermore, animals that hunt and ingest rodents, such as cats and dogs, may also infect humans with RBF through a bite, scratch, or secretions.

Risk Factors

Those who live in rat-infested environments are at greatest risk for RBF. Persons living in Asian countries, such as Japan, where the farming of rice attracts large numbers of rats, are more likely to be infected. However, RBF is also present in impoverished North American cities, which often provide a haven for rodent populations. Sanitation and sewage workers are also at high risk of RBF because of daily rodent contact. Laboratory staff are equally vulnerable to RBF because they regularly handle rats and clean their cages; pet store staff are also susceptible to RBF because of increased exposure to pet rats.

Symptoms

Symptoms of RBF include a rash, headache, chills, fever, vomiting, swelling of
the lymph
nodes, skin irritation, wounds that do not heal, and muscle,
joint, and back pain. In particular, the area around the rat bite sometimes
becomes reddish purple and swollen and ulcerated.

Screening and Diagnosis

After a physical examination, blood and culture tests are performed to confirm
a diagnosis of RBF. The tests determine if S. moniliformis or
S. minus bacteria are in the person’s blood, skin, joint
fluid, or lymph nodes. Polymerase chain reaction tests and
blood antibody tests aid in the diagnosis of RBF.

Treatment and Therapy

RBF can be treated successfully in early stages of the disease with seven to
fourteen days of antibiotics, primarily penicillin,
doxycycline, and erythromycin. If left untreated, RBF is extremely dangerous and
can damage the heart, brain, and other vital organs; it can sometimes lead to death.

Prevention and Outcomes

Avoiding rat-populated environments is the best way to prevent RBF; however, if
contact with rats cannot be avoided, one should always wear gloves when handling
them or their droppings; one should also wash his or her hands often. Persons who
have been bitten by a rat should treat the wound with antiseptic immediately to
help prevent infection and should contact a physician for further
care.

Bibliography

Dvorak, Glenda, Anna Spickler, and James Roth. Handbook for Zoonotic Diseases of Companion Animals. Ames: College of Veterinary Medicine, Iowa State University, 2008.

Gratz, Norman. The Vector- and Rodent-Borne Diseases of Europe and North America: Their Distribution, Public Health Burden, and Control. New York: Cambridge University Press, 2006.

Hayashimoto, N., et al. “Isolation of Streptobacillus moniliformis from a Pet Rat.” Journal of Veterinary Medical Science 70 (2008): 493-495.

Peters, C. J. “Infections Caused by Arthropod- and Rodent-Borne Viruses.” In Harrison’s Principles of Internal Medicine, edited by Joan Butterton. 17th ed. New York: McGraw-Hill, 2008.

Suckow, Mark, Steven Weisbroth, and Craig Franklin. The Laboratory Rat. 2d ed. Burlington, Mass.: Academic Press/Elsevier, 2006.