Species: Rickettsia africae
Tick vector: Amblyomma (hard tick)
Tick host: primarily cattle and wild ungulates in rural areas, but will readily attach to humans
Only about 50% of patients with positive serologies report a tick bite.
Incubation period: averages 6 days
Asymptomatic or minimally symptomatic cases common.
Clinical features in symptomatic cases:
(1) low-grade fever
(2) rash (usually maculapular, sometimes vesicular or pruritic)
(3) one or more tache noire (eschar that develop at the feeding site)
(4) influenza-like symptoms
(5) myalgias
(6) neck stiffness or muscle pain
(7) variable arthralgias
(8) variable photophobia
(9) variable apthous stomatitis
(10) variable lymphadenitis draining eschars and/or lymphadenopathy
(11) variable headache, irritability and/or depressed mood (neuropsychiatric symptoms)
(12) nonfatal course
General laboratory findings:
(1) elevation in C-reactive protein
(2) absolute lymphopenia
(3) variable thrombocytopenia
(4) variable elevated liver function tests
Microbiological testing:
(1) positive serologic tests for R. africae (IgM antibody, or 4-fold rise in convalescent specimen IgG)
(2) cross-reaction with other rickettsial serologic tests
(3) Western blot
(4) PCR
