A. Overview of Diseases

1. Organisms
   1. Obligate intracellular parasites
   2. Appear as pleiomorphic coccobaccili
   3. Uncommon infections in USA
   4. Transmission usually by ticks or mites
2. Laboratory Diagnosis
   1. Early tests required serologic studies and are still frequently used
   2. Weil-Felix test uses Proteus bacterial strains (OX-19 or OX-2) for serologic diagnosis
   3. Complement fixation and microagglutination tests are also used
   4. Immunofluorescence (IMF) tests are available for most of the organisms
   5. Polymerase chain reaction (PCR) may be used in future for rapid identification
3. Typhus Group
   1. Endemic Typhus - Rickettsia typhi, fleas and rodents
   2. Epidemic Typhus - R. canada (North America), tickborne
   3. Epidemic Typhus - R. prowazekii (worldwide)
   4. Scrub Typhus - Orientia (Rickettsia) tsutsugamushi, wild rodents, mites
4. Spotted Fever Group (Found in USA)
   1. Rocky Mountain Spotted Fever (see below)
   2. Rickettsialpox - R. akari. Mites, rodents
   3. African Tick Bite Fever (see below)
   4. Mediterranean Spotted Fever - R. conorii. Tunisia and France
   5. Other, non-USA: Boutonneuse Fever, North Asian Rickettsiosis, Queensland Typhus
   6. Human Ehrlichiosis can strongly resemble spotted fever [7]
5. Others
   1. Coxiella burnetti
   2. Trench Fever - R. quintana. Body lice, humans. OX-19 negative
   3. Ehrlichiosis

B. Symptoms

1. Due to mainly vascular invasion by organisms
2. Skin lesions, purpuric, due to endothelial damage, sometimes thrombus formation
3. Interstitial myocarditis including chest pain and fatigue
4. Pneumonitis with shortness of breath
5. Marked fevers of varying degrees
6. Rocky Mountain Spotted Fever [4]
   1. Tickborne illness caused by R. rickettsii
   2. Carried by rodents and dogs
   3. Serologic diagnosis by OX-19+, 2+; IMF available for detection
   4. Abrupt fever, may be very high (>104°F)
   5. Pain in muscular groups, especially abdomonal
   6. Rash occurs on ~3-4th febrile day: macular, nonfixed, pink becoming maculopapular
   7. True purpura occur by day 4 and may coalesce to form ecchymoses
   8. Headache, restlessness, insomnia, deafness in active stages
   9. Acute renal failure may develop and is a very poor prognostic factor
   10. Development of ARF increases risk of death by 17-fold [3]
7. African Tick Bite Fever [2,6]
   1. Tickborne caused by R. africae and by R. conorii
   2. Found in Sub-Saharan Africa and Guadeloupe
   3. Maculopapular or vesicular rash generally minor, present in ~50% of patients
   4. Lymphadenopathy or lymphangitis ~50%
   5. Eschar at site of inoculation 95% (unusual for rickettsial infections)
   6. Myalgia in 63%

C. Treatment

1. Most of these infections will respond to tetracyclines or chloramphenicol
2. Mild and moderate Rocky Mountain Spotted Fever may not require antibiotics
3. Rapid defervescence after antibiotic treatment of scrub typhus is characteristic
   1. This is used as a diagnostic test for rickettsial infection
   2. Doxycycline and chloramphenicol resistant strains have been reported [1]
   3. Rifampicin 900mg daily added to doxycycline for 1 year is most effective [5]
4. Monitoring of serum creatinine, AST, sodium, bilirubin and blood counts required [3]
5. Supportive therapy

References

1. Watt G, Chouriyagune C, Ruangweerayud R, et al. 1996. Lancet. 348:86
2. Brouqui P, Harle JR, Delmont J, et al. 1997. Ann Intern Med. 157(1):119
3. Conlon PJ, Procop GW, Fowler GW, et al. 1996. Am J Med. 101(6):621
4. Samuels MA and Newell KL. 1997. NEJM. 337(16):1149
5. Watt G, Kantipong P, Jongsakul K, et al. 2000. Lancet. 356(9235):1057
6. Raoult D, Fournier PE, Fenollar F, et al. 2001. NEJM. 344(10):1504
7. Yawetz S and Mark EJ. 2001. NEJM. 345(22):1627 (Case Record)