Rickettsia akari

Rickettsialpox (R. akari)

Microbiology

• Disease caused by Rickettsia akari, an intracellular Gram-negative bacterium
• Unlike most rickettsiae, it has a plasmid

Epidemiology

• Transmitted by the house mouse mite (Liponyssoides sanguineus)
  • Rodents are the reservoir
• Most cases are in New York, but it is found worldwide
• Most likely rickettsiosis to be found in Ontario
• Homelessness and IV drug use are risk factors

Clinical Presentation

• Incubation period of 7 to 14 days
• Present with fever, vesicular rash, and eschar
  • Headache also common
• The eschar is painless, and appears as a papule about a week after innoculation, followed by vesicle that dries and leaves a brown or black eschar
• The rash is vesicular, but may be papulovesicular or any other type of rash
  • Lesions leaves black crust and heal without scarring
  • Spares palms and soles
  • Resolves in two to three weeks
• May find leukocytosis

Diagnosis

• Detection of a four-fold rise in convalescent titres by complement fixation or indirect fluorescent antibodies

Management

• Usually self-limited, resolving in 7 to 10 days, though antibiotics help
• Doxycycline 100 mg po bid for 2 to 5 days and 48 h after fever resolves