Rat-bite fever

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

Rat-bite fever occurs most often among laboratory workers who handle lab ratsin their jobs, and among people who live in poor conditions, with rodent infestation. Children are particularly likely to be bitten by rodents infestingtheir 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.

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 woundhad appeared completely healed, it suddenly grows red and swollen again. Thepatient 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.

In streptobacillary rat-bite fever, found in the United States, diagnosis canbe made by taking a sample of blood or fluid from a painful joint. In a laboratory, the sample 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 bemade by examining blood or a sample of tissue from the wound for evidence ofSpirillum minus.

Shots of procaine penicillin G or penicillin V by mouth are effective againstboth 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.

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 progressto cause extremely serious, potentially fatal complications. In fact, beforeantibiotics were available to treat the infection, streptobacillary rat-bitefever frequently resulted in death.

Prevention involves avoiding contact with those animals capable of passing onthe 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 water, only pasteurized milk, and water from safe sources,should be ingested.

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