Overview
- Definition
A group of diseases transmitted by ticks (less commonly by fleas and lice) infected with rickettsias – pleomorphic, intracellular bacteria that primarily affect the vascular endothelial cells and smooth muscle cells of small and medium vessels
Divided into spotted fever and typhus groups
- Classic triad with mild to severe organ dysfunctions (see “Systemic association”)
Fever
Headache and malaise
Rash
- Rocky Mountain Spotted Fever (RMSF) is the most common rickettsiosis in the United States
Pathogen: Rickettsia rickettsii
Potentially lethal
North Carolina, South Carolina, Oklahoma, Tennessee, Arkansas
>90% contracted between April and September
- Other spotted fever rickettsioses in the United States include
Rickettsia parkeri rickettsiosis (R. parkeri)
Pacific Coast tick fever (R. species 364D)
Rickettsialpox (R. akari)
- Symptoms
Conjunctival injection
Decreased visual acuity
Paracentral scotomas
Floaters
- Laterality
More commonly unilateral
- Course
Ocular disease is acute and self-limited.
- Age of onset
All age groups affected
- Gender/race
No gender or racial predilection
Anyone living in endemic areas with exposure to rickettsial reservoirs
Systemic association
While RMSF is considered the most potentially severe of all spotted fever rickettsioses, many rickettsial diseases can be complicated byAcute renal failure
Respiratory distress syndrome
Meningoencephalic syndrome (especially the typhus group)
Myocarditis
Hepatic failure
Fulminant RMSF: in individuals with G6PD deficiency, RMSF can result in severe hemolysis and anemia, with life-threatening complications, within 5 days of disease onset
Exam: Ocular
Anterior Segment
- Most common
Conjunctivitis
Conjunctival petechiae and hemorrhage
Conjunctival nodules
- Less common
Mild non-granulomatous anterior chamber (AC) inflammation
Keratitis and marginal ulcer
Iris nodules
Posterior Segment
- Most common
Mild vitritis
- Retinal vascular involvement in half the patients:
Perivascular white retinal lesions
Subretinal hemorrhage
White-centered hemorrhage
Arterial plaque similar to toxoplasmic Kyrieleis
- Less common
Choroidal lesions
Macular star
Branch retinal artery occlusion (BRAO)
Exudative retinal detachment (RD)
Anterior ischemic optic neuropathy
Exam: Systemic
Incubation period varies among different rickettsias, ranging 2–21 days
- Characteristic rash appears 3–5 days after constitutional symptoms, though rash never develops in some cases (“spotless fever”)
Typical progression: wrists/ankles → palms and soles → forearms, neck, face, axilla, buttocks, and trunk
Small, flat pinkish spots (macules) → darker and raised (papules) → papules may develop petechia and merge to form larger hemorrhagic patches (even gangrenous in severe cases)
Patients with spotted fever rickettsioses other than RMSF will have an eschar (dark scab) at the site of the tick or mite bite
Imaging
- Fluoresceine angiogram
Early hypofluorescence and late staining of large retinal lesions
Vascular leakage
Optic nerve staining
Blocked fluorescence from retinal hemorrhage
- Indocyanine green angiography
Mid-phase hypofluorescent dots if choroidal lesions are present
Laboratory and Radiographic Testing
Anti-rickettsia immunoglobulin G & M (IgG/IgM) and rickettsia deoxyribonucleic acid (DNA) amplification via polymerase chain reaction (PCR) are offered at commercial laboratories
- Complete blood count (CBC) is nonspecific, but may show
Thrombocytopenia
Hyponatremia
Elevated liver function tests (LFTs)
Differential Diagnosis
Ehrlichioses (Ehrlichia chaffeensis and Ehrlichia ewingii)
Human granulocytic anaplasmosis (Anaplasma phagocytophilum)
Measles
Dengue fever
Meningococcemia
Leptospirosis
Toxic shock syndrome (S. aureus)
Syphilis
Treatment
Treat suspicious cases empirically, as serologies can take 1–2 weeks
Doxycycline is the treatment of choice
Chloramphenicol 50–75 mg/kg/day in tetracycline allergy
Fluoroquinolones show efficacy anecdotally; penicillin, cephalosporine, and aminoglycosides are ineffective
Patient should be afebrile for at least 3 days before antibiotic discontinuation
Topical tetracycline for conjunctivitis and keratitis
Topical corticosteroids for anterior uveitis
Referral/Comanagement
Infectious disease