Definition of Rat-bite fever:

Rat-bite fever is an infectious disease spread by fluids in the mouth or nose or urine of an infected rodent.

Causes, incidence, and risk factors:

Rat-bite fever can be caused by two different organisms, Actinobacillus muris (formerly called Streptobacillus moniliformis) and Spirillum minus. Most reported cases of rat-bite fever occur in Japan, but the disease has also been seen in Australia, Africa, North and South America, and Europe.

Most people get rat-bite fever through contact with urine or oral (mouth) or conjunctival (eye or nose) secretions from an infected animal. This most commonly occurs via a bite, yet some cases may occur simply through contact with these secretions. The source of the infection is usually a rat, but other animals such as squirrels, weasels, and gerbils, may be the source.

In rat-bite fever due to Actinobacillus muris, fever, chills, headache, and muscle pain usually occur within 10 days of exposure. This is followed within three days by a diffuse rash, primarily in the extremities. One or several large joints may become swollen, red, and painful. If untreated, severe complications including infection of the heart valves may occur.

The illness caused by Spirillum minus is common in Asia, particularly Japan, where it is called sodoku. In this form of rat-bite fever, a particular skin rash characterized by red or purple plaques is frequently seen, and the previously healed wound at the site of the bite may reactivate and open. Joint involvement is rare.