infectious diseases
Rat Bite Fever
Diagnosis of Rat Bite Fever
Clinical evaluation Culture (of the streptobacillary form) and sometimes rising antibody titers The diagnosis of rat-bite fever is clinical. The two forms usually can be differentiated clinically from one another: Bite site: The bite site in streptobacillary rat-bite fever, if present, typically heals quickly, with minimal residual inflammation and without significant regional lymphadenopathy, whereas the bite site in spirillary rat-bite fever persists, becomes indurated, and may ulcerate, with associated regional lymphadenopathy. Joints: In streptobacillary rat-bite fever, migratory polyarthralgia is frequent and septic arthritis of large joints occurs in some patients, whereas in spirillary rat-bite fever, joint manifestations are rare. Skin: The rash in streptobacillary rat-bite fever is maculopapular, petechial, or purpuric and hemorrhagic vesicles that may develop on the peripheral extremities, especially the hands and feet, are very tender to palpation. The rash in spirillary rat-bite fever is red-brown macules with occasional urticaria. Diagnosis of streptobacillary rat-bite fever is confirmed by culturing the organism from blood or joint fluid. Measurable agglutinins develop during the second or third week and are diagnostically important if the titer increases. Polymerase chain reaction (PCR) or enzyme-linked immunosorbent assay (ELISA) tests may be helpful. The white blood cell count ranges between 6,000 and 30,000/mcL (between 6 and 30 × 109/L). Nontreponemal syphilis serologic tests (Venereal Disease Research Laboratory [VDRL] or rapid plasma reagin [RPR] tests) may be falsely positive. Diagnosis of spirillary rat-bite fever is confirmed by Direct visualization ofSpirillumfrom blood smears or tissue from lesions or lymph nodes Giemsa stain or darkfield examination of blood from inoculated mice Direct visualization is required becauseS. minuscannot be cultured on synthetic media. The WBC count ranges between 5,000 and 30,000/mcL (between 5 and 30 × 109/L). The VDRL results are false-positive in half the patients. The disease may easily be confused with Malaria or 