Classification: ICD-9 082.0; ICD-10 A77.0
Syndromes and synonyms: Rocky Mountain spotted fever (RMSF), North American tick typhus, New World spotted fever, Tick-borne or tick typhus, Tobia fever (Colombia), Sao Paulo fever or ‘febre maculosa’ (Brazil), and fiebre manchada (Mexico).
Agent: Rickettsia rickettsii, R. parkeri and R. africae, Gram-negative intracellular bacilli. R. rickettsii is the agent of RMSF, R. parkeri causes a RMSF-like illness. R. africae causes African tick bite fever and is rarely found in the new world. New agents are still being discovered regularly.
Reservoir: Hard ticks (Ixodidae). Depending on the tick species, they can acquire infection via feeding on animals with rickettsemia, or via venereal, transovarial, and trans-stadial passage. Animals preferred for feeding varies by tick species and their life stage. Rodent hosts include ground squirrels, mice, and voles.
Vector: The Ixodid ticks are both vector and reservoir. Amblyomma americanum, Dermacentor andersoni and D. variabilis (American dog tick) in Canada and the USA, Rhipicephalus sanguineus in Mexico and Central America, and A. cajennense from the southern states of the USA southwards as far as Argentina. D. variabilis is the primary vector for RMSF in the USA. A. maculatum is the main vector of R. parkeri in North America and A. triste in South America.
Transmission
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