Rat bite fever is an infection caused by the bacterium Streptobacillus moniliformis (the main cause in most countries) or Spirillum minus (the main cause in Asia). The condition is, not surprisingly, associated with being bitten by a rat, although it can be transmitted by other routes such as dog bites. The bacteria live in the mouths of most rats (and a less-well-understood percentage of other animals). Disease occurs when these bacteria make it into the body via a bite, or other high-risk contact such as kissing the animal or letting it lick an open wound.
The Australian case report describes a 26-year-old woman who had a fever and sore throat, which progressed to a severe unrelenting headache with nausea, vomiting, sensitivity to light, neck stiffness and pneumonia. Streptobacillus moniliformis was isolated from a blood sample. The strain was fortunately susceptible to the antibiotics that had been started earlier. It wasn't until a couple of days later that a rash (a classic sign of rat bite fever) developed. Fortunately at that point the diagnosis had already been made and the woman was responding to treatment.
After "further history taking" it was revealed that the patient owned two rats and, while she had not been bitten, she had close contact with them, including kissing. It's not clear when the "further history taking" occurred, but it probably happened after they found the S. moniliformis and made diagnosis, which rounds out the case report nicely but doesn't speed up the diagnosis or improve case care. The animal contact question needs to be asked at the start. One of the Lessons from Practice that the article highlights is "A thorough history, including history of animal exposure and pet ownership, should be taken for all febrile patients." Remove "febrile" and I agree completely.
Anyway, the woman responded to treatment and went home after 17 days in hospital. Most people that are properly diagnosed and treated survive, but rat bite fever can be fatal.
Most rats carry at least one of the two bacteria that cause this disease. There's no indication to test pet rats (since we assume they all have the bug until proven otherwise, and we can't confidently prove otherwise) or treat them (since we have no evidence we can eliminate the bug from the mouth of a healthy rat). It's a limited but ever-present risk of rat ownership, and one that can be greatly reduce by avoiding kissing rats, preventing bites, proper wound care should bites occur, and ensuring that physicians know about potential rat contact if illness develops.