Lesson 5 Ricket

• Rickettsial Infections


  • Spotted Fever Group
  • Typhus Group
  • Traditional Group
  • Q Fever
  • Trench Fever
  • Ehrlichiosis
• Rickettsial infections


  • Transmitted by the bite of arthropods like ticks, mites, lice, and fleas except for Q fever, which is transmitted by inhalation of aerosols
  • Zoonotic (with animal reservoirs) except for Epidemic typhus which occurs only in humans
• Rocky Mountain Spotted Fever


  • Very small size (0.3 x 1-2 um)
  • Have gram-negative cell wall composed of peptidoglycan, muramic acid, and diaminopimelic acid
  • Stain poorly with Gram stain but stain well using Giemsa or Gimenez stain
  • Pleomorphic - cocci or short bacilli
  • Obligate intracellular parasites
  • Easily destroyed by heating, dyeing, and bactericidal agents like tetracycline
  • Growth enhanced by sulfonamide
  • Common in the mountainous areas of the United States
• Rickettsialpox


  • Eschar: blackened scab
  • Fever, headache, chills, myalgia
  • Signs and symptoms like varicella
  • Firm red macule at bite site
• Epidemic Typhus


  • Also known as "Louse-borne Typhus", "Camp Fever", "Jail Fever" or "War Fever"
  • Maculopapular rashes, although there is sparing of the soles and palms
  • It also presents with more severe systemic infection and prostration, and is more fatal
  • This is associated with a recrudescent infection known as Brill-Zinsser Disease
• Prevention of Epidemic Typhus

  1. Body lice thrive in overcrowded

  2. Bathe regularly; change into clean clothes

  3. Wash louse-infested clothing

  4. Machine wash and dry infested clothing and bedding using hot water (at least 130°F) and dry on high heat when possible

  5. No vaccine
• Endemic Typhus


  Also known as "Murine Typhus"
• Scrub Typhus


  • Similar to Epidemic Typhus except for the eschar (punched out ulcer covered with blackened scab)
  • With associated lymphadenopathy and lymphocytosis
  • May involve severe cardiac and cerebral complications
• Q Fever


  • Also called "Query Fever"
  • Similar to Influenza and non-bacterial pneumonia, hepatitis, or encephalopathy
  • It does not present any rash or local lesion
• Trench Fever


  Headache, Exhaustion, pain, sweating, cold extremities, and fever with roseola rash
• Ehrlichiosis


  • Parasitize lymphocytes, neutrophils, and monocytes
  • Non-specific symptoms with thrombocytopenia
• Relapsing Fever


  • Very flexible and highly motile (rotatory and twitching)
  • It can survive low temperature (4ºC) in blood or culture for months
  • Fever, headache, chills
  • Fever lasts for few days then resolve
  • Fever recurs withs multi-organ dysfunction
• Laboratory Diagnosis of Relapsing Fever

  1. Examination of peripheral blood smear using Giemsa or Wright stain will show spirochetes

  2. Culture using special media

  3. Serological tests
• Prevention of Rickettsial Infections

  1. Avoidance of areas infested by arthropod vectors

  2. Protection from bites
• Lyme Disease


  • 1st stage: painless, circular red rash at site of bite; Spreading with a clear center (thus called as erythema chronicum migrans) accompanied by arthralgia
  • 2nd stage: After few weeks or months. Myocarditis or pericarditis, aseptic meningitis, Bell's palsy & neuropathies. Followed by latent prd
  • 3rd stage – arthritis involving large joints (knees) & progressive chronic central system
• Treatment of Lyme Disease

  1. Mild infection: amoxicillin or doxycycline

  2. Late-stage infection: penicillin G or Ceftriaxone