Rocky Mountain Spotted Fever

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Contents 1 Introduction 2 Etiology 3 Epidemiology 4 Pathology 5 Clinical-manifestations 6 Laboratory 7 Complications 8 Differential-diagnosis 9 Management 10 More General Terms 11 Additional Terms 12 References

Introduction

• Tick-borne infection caused by Rickettsia rickettsii characterized by sudden onset of fever, severe headache, myalgia & characteristic rash.

Etiology

• etiologic agent: Rickettsia rickettsii
• transmitted through bite of infected tick or inoculation through abrasion with thick feces or body fluids
• exposure to ticks occurs in tick- infested areas or in association with dogs who bring the tick to the patient

Epidemiology

• 95% of patients become ill between April 11 & Sept. 30
• occurs only in western hemisphere
• cases reported in all states except Vermont & Hawaii
• North & South Carolina, Oklahoma & Tennessee account for 48% of cases in US
• 600 cases reported annually in US
• only 60% of patient remember recent tick bite (within 2 weeks)
• ticks transmitting Rickettsia rickettsii

• Dermacentor andersoni ( wood tick), western USA
• Dermacenter variabilis ( dog tick)

• eastern 2/3 & areas of west coast USA

• Rhipicephalus sanguineus, Mexico
• Amblyomma cajennense, Mexico, Central & South America

Pathology

• H&E: necrotizing vasculitis
• direct immunofluorescence microscopy: R rickettsii- specific antigen within endothelial cells
• pathophysiology:

• initial replication of R rickettsii in endothelial cells
• followed by hematogenous dissemination
• organisms attach to vascular endothelial cells
• R rickettsii spreads from endothelial cell to endothelial cell forming a network of infected endothelial cells
• rash results from extravasation of blood after vascular necrosis
• cases of severe infection of brain & lung have a high mortality

Clinical-manifestations

• incubation period: 3-14 days, mean: 7 days after tick bite
• prodrome: anorexia, irritability, malaise, feverish feeling
• onset of symptoms is generally abrupt

• fever (94%), up to 40 degrees C
• severe headache (86%)
• generalized myalgia, especially back & legs (83%)
• rigors
• photophobia
• nausea with vomiting
• dyspnea, cough [3]

• rash

• 14% have rash on day 1, 49% have rash within 3 days, 20% have rash after 5 days, 10-13% have no rash
• early lesions: 2-6 mm, pink, blanchable macules
• in 1-3 days, macules evolve to red papules
• in 2-4 days lesions become hemorrhagic
• necrosis of the skin & underlying tissue may occur, especially fingers, toes, ears, scrotum
• distribution: generally rash begins on wrists, forearms & ankles; later appears on palms & soles; within 6-18 hours rash spreads centripetally to arms, thighs, trunk & face (distribution distinguishes from ehrlichiosis)

• variant presentations

• spotless fever (13%), diagnosis often missed
• abdominal syndrome, may mimick acute abdomen
• thrombotic thrombocytopenic purpura

Laboratory

• complete blood count ( CBC): thrombocytopenia
• serology

• immunofluorescent antibody (IFA) or ELISA for IgM & IgG anti- Rickettsial antibodies
• 4-fold increase in titer between acute & convalescent titers is diagnostic
• a titer of > 64 is detectable between days 7-10 of illness

• skin biopsy

Complications

• extensive cutaneous necrosis secondary to DIC, with gangrene of extremities requiring amputation
• hypotensive shock
• hepatomegaly, splenomegaly, GI hemorrhage, altered consciousness, transient deafness, incontinence, oliguria, secondary bacterial infections of the lung, ear, parotid gland
• death

• associated with old age, delay in treatment & treatment with chloramphenicol
• untreated fatality is 20-23%; if treated within 5 days of presentation, fatality is 3%, 6% if > 40 years of age
• death generally occurs within 5-15 days

• long-term sequelae

• neurologic: paraparesis; hearing loss; peripheral neuropathy; bladder & bowel incontinence; cerebellar, vestibular & motor dysfunction; language disorders
• disability from limb amputation
• scrotal pain following cutaneous necrosis

Differential-diagnosis

• meningococcemia

• nuchal rigidity, DIC, palpable purpura, petechiae

• disseminated gonococcal infection
• secondary syphilis
• Staphylococcus aureus septicemia
• toxic shock syndrome
• typhoid fever
• leptospirosis
• other Rickettsial infections

• ehrlichiosis

• macules, papules & petechiae (1/3)
• rash: central distribution, peripheral sparing
• leukocyte or monocyte intracytoplasmic inclusions (morulae)

• murine typhus
• epidemic typhus
• rickettsialpox

• viral exanthem

• measles
• varicella
• rubella
• enterovirus

• adverse cutaneous drug reaction
• immune complex vasculitis
• idiopathic thrombocytopenic purpura
• thrombotic thrombocytopenic purpura
• Kawasaki's syndrome

Management

• treatment within 5 days of presentation reduces mortality for 20% to 6% [3]
• doxycycline 100 mg PO/ IV BID

• drug of choice in adults & children > 8 years
• contraindicated in pregnant women

• tetracycline 25-40 mg/kg/day divided QID
• chloramphenicol if pregnant, 50-75 mg/kg/day divided QID
• supportive therapy

• shock
• acute renal failure
• respiratory failure
• prolonged coma

• prognosis: in uncomplicated cases, defervescence generally occurs within 48-72 hours of initiating therapy

More General Terms

• tick borne infection
• skin disease (dermatologic disorder, dermatopathy, dermatosis)
• Rickettsia infection

Additional Terms

• Rickettsia rickettsii
• tick bite

References

1. Color Atlas & Synopsis of Clinical Dermatology, Common & Serious Diseases, 3rd ed, Fitzpatrick et al, McGraw Hill, NY, 1997, pg 762-765
2. Centers for Disease Control and Prevention (CDC) Recommendations on diagnosis and management of tickborne rickettsial diseases: Rocky Mountain spotted fever, ehrlichioses, and anaplasmosis [1]
3. Medical Knowledge Self Assessment Program (MKSAP) 14, 15, American College of Physicians, Philadelphia 2006, 2009

Rocky Mountain spotted fever (RMSF)