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Background
- Most frequent rickettsial disease reported in the US.[1]
- Caused by Rickettsia rickettsii
- Obligate intracellular, gram negative bacteria
- Predilection for vascular endothelial cells
- Spread by ticks
- American Dog Tick (Dermacentor variabilis) Most common vector
- Rocky Mountain Wood Tick (Dermacentor andersoni)
- Brown Dog Tick (Rhipicephalus sanquineus)
- Cayenne Tick (Amblyomma cajennense)
- Seasonal distribution with most infections occurring in the summer months
- Widely distributed in the US
- States with the highest incidence are Oklahoma, Nebraska, Arkansas, Tennessee and North Carolina
- Overall incidence is increasing while mortality is falling[2]
- Prior to the era of antibiotics, ~30% mortality
- Currently mortality is 3-5%
Clinical Features
- Symptoms generally begin 2-14 days after inoculation from an infected tick[3]
Early symptoms
Late symptoms
Rocky mountain spotted fever rash
- Rash
- Begins as a blanching maculopapular rash that evolves to become a petechial rash
- Usually 2-5 days after fever subsides
- Starts on extremities and spreads inward (centripetally)
- Can involve palms and soles (50% of cases)
- Arthralgias
- Positive Rumpel-Leede test
- Development of petechiae at the site of blood pressure cuff and distally after compression
Complications
- Secondary to host response against infected endothelial cells
Differential Diagnosis
Lower Respiratory Zoonotic Infections
Evaluation
- PCR (initially)
- Serial serologic examinations by indirect fluorescent antibody confirm the diagnosis
- Titers
Work-Up
Management
- Doxycycline 100 mg BID for 5-7 days[4]
- Indicated also in children at 2.2mg/kg BID
- Chloramphenicol (CAM) 50-100 mg/kg/day div Q6hr (Max dose = 4g/day)
- Preferred agent in pregnancy. May cause aplastic anemia and Grey baby syndrome, more common in near term or 3rd trimester[1]
- Consideration should be made for doxycycline over CAM in the 3rd trimester
Disposition
See Also
References
