Infection in Animals

The primary hosts of Streptobacillary RBF are rats, both the black rat (Rattus rattus) and the Norwegian rat (Rattus norvegicus), kept as pets and used in animal research. These animals can carry and spread the bacteria throughout their lives without showing signs of illness. Other rodents can also carry and spread the bacteria.

The bacteria live in the upper respiratory tract of rats and other rodents. Studies have shown that many domestic rats and over half of wild rats carry S. moniliformis.

Other rodents that can carry the bacteria are:

• Mice, guinea pigs, gerbils, and squirrels
• Infrequently, dogs, cats, ferrets, weasels, cattle, pigs, koalas, non-human primates, and turkeys, but this is not well documented

The bacteria may spread to these animals after they consume contaminated food or water, or after direct contact with rats. These animals may or may not show signs of illness.

People can become infected with the bacteria after being bitten or having contact with an animal carrying the bacteria. One study showed that dogs that had been in close contact with wild rats had S. moniliformis DNA in their mouths. Additionally, a human case of RBF occurred after the patient was bitten by a dog known to eat rats.

There are currently no laboratory tests that can accurately tell whether or not an animal is infected with S. moniliformis or S. minus. The bacteria can sporadically be in an animal’s saliva, urine, and feces, so a negative test might not mean the animal is actually free of the bacteria.  There is also no data to support the use of antibiotics to get rid of S. moniliformis or S. minus in animals carrying these bacteria.