Scrub Typhus Masquerading As Infectious Mononucleosis: A Case Report

Scrub typhus is a tick-borne disease caused by the intracellular organism <i>Orientia tsutsugamushi</i>. It typically presents with the cardinal "triad" of fever, rash, and eschar, along with other nonspecific symptoms. We report a case of scrub typhus in a 74-year-old man who did not exhibit the typical rash. He presented to the emergency room with a one-week history of generalized symptoms, including fever, throat pain, and myalgia, and was admitted due to suspected cholangitis based on elevated liver enzymes. However, computed tomography (CT) and magnetic resonance cholangiopancreatography (MRCP) ruled out this diagnosis. A transient rash developed after the initiation of antibiotics, considered to be a drug reaction. Further laboratory workup showed mildly positive results for cytomegalovirus (CMV)-IgM, and subsequent tests revealed an elevation of atypical lymphocytes, leading to a misdiagnosis of acute CMV infection. During a subsequent physical examination, an initially overlooked eschar was identified on his medial malleolus. Serology tests showed highly elevated <i>Orientia tsutsugamushi</i> IgM and IgG levels and treatment with tetracycline led to full recovery. Paired serology after two weeks showed no elevation in CMV antibodies, and the initial positive CMV-IgM result was considered insignificant. Scrub typhus can manifest with a wide range of symptoms, underscoring the importance of a thorough physical examination and maintaining clinical suspicion, especially in febrile patients in endemic areas.