MEDizzy - A 22-year-old hiker living in western North Carolina

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General Pathology (II)

A 22-year-old hiker living in western North Carolina develops fever, chills, headaches, and myalgia after being bitten by a tick. Examination of his peripheral blood reveals rare “asterisk-shaped” inclusion bodies in his neutrophils. What is the most likely cause of his illness?

ExplanationEhrlichiosis is a tick-transmitted disease caused by Rickettsiales, which infects either neutrophils (E ewingii) or macrophages (E chaffeensis). Cytoplasmic inclusions within leukocytes are “asterisk” or “mulberry” shaped. Clinical symptoms include the abrupt onset of fever, headache, and malaise. The disease may progress to respiratory and renal failure with shock. A rash is less often present than is seen with RMSF. Many patients diagnosed with RMSF who do not have a rash probably have ehrlichiosis. Psittacosis is a respiratory disorder caused by infection with C psittaci, an obligate intracellular bacterium. It is primarily an occupational disease of zoo and pet employees and poultry farmers. Tularemia is caused by F tularensis. Infection is spread to humans from ticks and rabbits. Three clinical forms of tularemia are typhoidal (with systemic symptoms), pneumonic, and ulceroglandular. Some lesions may develop caseating granulomas. Nocardiosis is caused by the filamentous gram-positive, partially acid-fast, bacteria N asteroides. Nocardia infection can involve either the lungs (producing progressive pneumonia) or skin (producing mycetoma). Patients who develop nocardiosis are often immunosuppressed.