Rickettsia

Rickettsial Infections Overview

Introduction

• Rickettsia: A group of vector-borne organisms causing acute febrile illnesses worldwide.
• Clinical Presentation: Similar across rickettsial infections but varies by species and region.
• Importance: Early recognition and treatment are crucial due to significant morbidity and mortality.

Etiology

• Causative Agents: Obligate intracellular bacteria in the genus Rickettsia.
• Four Categories:
  • Spotted Fever Group: Includes R. rickettsii (Rocky Mountain spotted fever), R. africae (African tick bite fever), R. conorii (Mediterranean spotted fever).
  • Typhus Group: Includes R. prowazekii (epidemic typhus) and R. typhi (murine typhus).
  • Ancestral Group: Includes R. bellii and R. canadensis.
  • Transitional Group: Contains species with traits of both spotted fever and typhus groups.
• Species Examples:
  • North America: R. rickettsii causes Rocky Mountain spotted fever.
  • Sub-Saharan Africa: R. africae causes African tick bite fever.
  • Europe and North Africa: R. conorii causes Mediterranean spotted fever.

Epidemiology

• Transmission Vectors: Ticks, body lice, mites, and fleas.
• Accidental Hosts: Humans are typically accidental hosts.
• Regional Vectors:
  • United States:
    • Dermacentor variabilis (American dog tick).
    • Dermacentor andersoni (Rocky Mountain wood tick).
    • Amblyomma americanum (Lone Star tick).
  • South America: Amblyomma cajennense.
  • South Africa: Amblyomma hebraeum, Amblyomma variegatum.
• Seasonality: More common in warmer months.
• Specific Conditions:
  • Epidemic Typhus: Transmitted by body lice, associated with crowded conditions and poor hygiene.
  • Murine Typhus: Common in tropical and subtropical areas, transmitted by flea bites.

Pathophysiology

• Target Cells: Infects vascular endothelial cells lining small and medium vessels.
• Systemic Effects: Disseminated inflammation, loss of barrier function, altered vascular permeability.
• Symptoms: Fever, myalgias, headache, confusion, rash, cardiovascular instability.
• Severe Cases: High mortality.
• Mechanisms: Rapid entry into cells, downregulation of immune pathways (under study).

History and Physical

Commonly a small, hard, black sore (called an eschar) first appears at the bite site where the infection was introduced

• Symptom Onset: 4-10 days post-exposure.
• Classic Triad: Fever, headache, petechial or maculopapular rash.
• Additional Symptoms:
  • Lymphadenopathy.
  • CNS changes (confusion, nuchal rigidity).
  • Eschar at inoculation site.
  • Myalgias and arthralgias.
  • Hepatitis.
  • Vomiting.
  • Cardiovascular instability.
• Suspicion: High index of suspicion needed during summer months.
• Exposure History: Detailed travel and outdoor exposure history are essential

Evaluation

• Diagnostic Tests:
  • Serologic Response: IgG and IgM to R. rickettsiae.
  • Molecular Tests: PCR in some centers.
  • Skin Biopsy: Used in certain cases.
• Laboratory Findings:
  • Thrombocytopenia.
  • Hyponatremia.
  • CSF pleocytosis.
  • Peripheral WBC count: May be elevated, normal, or low.
• Clinical Suspicion: Crucial given potential for negative serologic testing early in the course.

Treatment / Management

• First-Line Treatment: Doxycycline.
  • Dosage and Duration: Varies by specific organism.
• Alternatives:
  • Severe Disease/Allergy: Chloramphenicol.
  • Milder Disease: Macrolides (e.g., clarithromycin).
• Contraindications: Fluoroquinolones are not recommended.
• Children <8 Years: Doxycycline indicated for severe rickettsial infections due to high mortality risks.
• Early Treatment: Do not delay awaiting confirmatory testing.

Differential Diagnosis

• Dengue
• Emergent management of malaria
• Group A streptococcal infection
• Kawasaki disease
• Leptospirosis
• Measles
• Meningococcal infection
• Pediatric rubella
• Pediatric syphilis
• Pediatric toxic shock syndrome
• Vasculitis and thrombophlebitis

Prognosis

• Severity: Varies by species and host factors.
• Virulent Species: R. rickettsii and R. prowazekii have significant mortality if untreated.
• Early Treatment: Effective with excellent outcomes.

Complications

• Common with Delayed Treatment: Gangrene, hearing loss, bowel/bladder incontinence, partial paralysis of lower extremities.

Deterrence and Patient Education

• Prevention: Avoid vector exposure (ticks, lice, mites, fleas).
• Protective Measures:
  • Inspection for insects post-outdoor activities.
  • Wearing long-sleeved clothing and insect repellant.
• Education: Awareness of endemic areas.

Enhancing Healthcare Team Outcomes

• Interprofessional Management: Involves pharmacists, nurses, and other healthcare professionals.
• Prevention Focus: Education on avoidance and protective measures.
• Team Coordination: Improved care coordination and communication enhance outcomes.