A 9-year-old child is brought to the emergency room with the chief complaint of enlarged, painful axillary lymph nodes. The resident physician also notes a small, inflamed, dime-sized lesion surrounding what appears to be a small scratch on the forearm. The lymph node is aspirated and some pus is sent to the laboratory for examination. A Wahin-Starry silver impregnation stain reveals many highly pleomorphic, rod-shaped bacteria. The most likely cause of this infection is

While the essential information (i.e., the evidence that the child in question was scratched by a cat) is missing, the clinical presentation points to a number of diseases, including catscratch disease (CSD). Until recently, the etiologic agent of CSD was unknown. Evidence indicated that it was a pleomorphic, rod-shaped bacterium that had been named Afipia. It was best demonstrated in the affected lymph node by a silver impregnation stain. However, it now appears that Afipia causes relatively few cases of CSD and that the free-living rickettsia primarily responsible is Rochalimaea henselae, which has recently been renamed Baonella henselae. Reference: Ananthanarayan and Paniker&;s Textbook of Microbiology Tenth edition