Rat bite fever caused by different bacteria (1)streptobacillus moniliformis (2)spirillum minus both of which are natural parasites of rodents.spirillary RBF have incubation period of 1_4 weeks.rat bite wound which may have healed suppurates at the onset of fever with regional lymphadenopathy Ref:Anantnarayan and paniker's microbiology 10th edition