While it's commonly transmitted through a bite or scratch from an infected rodent, rat-bite fever (RBF) may also be caused by consuming contaminated food or water. When RBF is a foodborne illness, it's called Haverhill fever, and it causes fever, headache, joint and muscle pain and rash, just like RBF. But in addition to all that, the foodborne version also causes severe gastrointestinal distress and pharyngitis.
RBF, and by association Haverhill fever, is a bacterial infection that can be caused by two different bacteria depending where in the world you live: The Streptobacillus moniliformis bacterium is responsible for streptobacillary RBF infections in North America, while Spirillum minus causes spirillary RBF (also known as sodoku), primarily in Asia.
Haverhill fever is caused by consuming food, milk or water that's been in contact with infected rodents — specifically, sorry to say, food contaminated with Streptobacillus moniliformis bacterium through rat feces or urine. Consider that just one rat may have between 20 and 50 droppings and about a half an ounce (14 millileters) of urine every day, and then consider what that looks like after 6 litters of rats have infested the space [source: Chamberlain]. It's easy to see how even a small rat problem can cause a lot of contamination.