Rocky Mountain spotted fever

Definition

A life-threatening rickettsial disease caused by *Rickettsia rickettsii* and transmitted to humans and dogs primarily through the bite of infected hard ticks (family Ixodidae), especially *Dermacentor* species. Despite its name, the disease occurs throughout the Americas. In vectors, the bacterium invades tick tissues and is transmitted transstadially and transovarially, maintaining infection across life stages and generations. Clinical presentation in humans includes acute fever, headache, and a characteristic spotted rash that typically begins on extremities and spreads centripetally; untreated cases carry significant mortality.

Etymology

Named for the Rocky Mountain region where it was first identified in the late 19th century; 'spotted' refers to the hemorrhagic rash.

Example

In the eastern United States, *Dermacentor variabilis* (American dog tick) is the principal vector of Rocky Mountain spotted fever, acquiring *R. rickettsii* while feeding on infected small mammals and subsequently transmitting the pathogen to humans during later blood meals.

Synonyms

• RMSF
• blue disease
• black measles

Related Terms

• tick-borne disease
• rickettsiosis
• Dermacentor
• vector competence
• Transovarial transmission
• spotted fever group rickettsiae
• Tick paralysis

Usage Notes

The name is misleading geographically: highest contemporary incidence is in the southeastern and south-central United States, not the Rocky Mountains. Distinguish from 'Rocky Mountain fever' (undifferentiated historical term) and from other spotted fevers caused by related *Rickettsia* species. In entomological literature, often discussed alongside vector biology, tick-host associations, and acarological surveillance rather than clinical medicine.