When assaulted with antibiotics, for instance, B. burgdorferi seems to retreat into a defensive, impervious form, a sort of cystlike stage known as a “round body.” Round bodies are resistant to destruction and very difficult to detect. A patient who seems cured of Lyme disease by the standard two-to-four-week course of amoxicillin or doxycycline might still be harboring round bodies and therefore subject to relapse.
