Rickettsial infections


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A comprehensive description about various rickettsial infections encountered in Pediatrics

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Rickettsial infections

  1. 1.  Group of bacteria that are fastidious, obligate intracellular pathogens They are pleomorphic & coccobacillary The organisms will not show up on Gram stain, but can be seen when either Gimenez or Giemsa stains are used
  2. 2.  Spotted Fever Group Typhus Group Transitional group The Others The outer membrane protein A (ompA) gene is present in spotted fever but not typhus group organisms
  3. 3.  Rickettsia are usually introduced into human skin by the bite of an insect (flea or louse) or an arachnid (tick or mite) These arthropods serve as both host and vector to the rickettsia and reside on the reservoir animals (dogs, mice, rats, and flying squirrels)
  4. 4.  Two of the rickettsial diseases are unique in that humans may acquire them by direct inhalation Q fever (Coxiella burnetii) Epidemic typhus (Rickettsia prowazekii)
  5. 5. Disease Rickettsial Agent Insect Vector Mammalian ReservoirIndian tick typhus R.conorii Tick Dog/RodentsRMSF R.rickettsi Tick Dog/RodentsRickettsial pox R.akari Mite Mice
  6. 6. Disease Rickettsial Agent Vector Mammalian ReservoirEpidemic typhus R.prowazeki Louse HumansMurine typhus R.typhi Flea RodentScrub typhus R.tsusugamushi Mite Rodent
  7. 7.  very similar for all infections regardless of species Vasculitis caused by the invasion and multiplication of the organism in the endothelial and smooth muscle cells of the blood vessels
  8. 8.  Thrombosis, occlusion, and necrosis of blood vessel walls Thrombocytopenia with hemorrhage Massive capillary leakage into the interstitial spaces results in edema, hypovolemia, hypotension, and adult respiratory distress syndrome (ARDS) Encephalitis, myocarditis, & nephritis are the common clinical consequences Hyponatremia is due to ADH response
  9. 9.  Rocky Mountain spotted fever Murine (Endemic) typhus Epidemic typhus Q fever
  10. 10.  IP: 2 to 14 days H/o exposure to tick/ close contact with pets/ Endemic area/ similar illness in family
  11. 11.  Initial Non-specific symptoms – Calf muscle pain and tenderness are more common in children. Gastro-intestinal symptoms are more commonly associated Skin rash: 2-4 days after onset of illness.
  12. 12. FeverHeadache Rash
  13. 13. Necrotic petechiaeMaculopapular
  14. 14.  Rocky Mountain spotted Fever: -Rash typically appears on 4th day as blanching maculopapular lesions on the extremities Louse borne or Epidemic typhus: -Rash first appears in axillary folds then involving the trunk and extremities. - Brill-Zinsser disease
  15. 15.  Murine (fleaborne or endemic) typhus: - Relatively mild illness with less complications -Rash is non-purpuric,non-confluent,less extensive -History of a flea bite and the presence ofrats in the house support the diagnosis butthis is only reported 30% of the time.
  16. 16.  Scrub typhus: -Occurs mostly in Asian countries -characterised by painless eschar and “satellite lymphadenopathy” Rickettsial pox: -best known because of its association with a varicelliform rash.
  17. 17.  Usually does not affect children No vector is involved Presents as both acute or chronic forms Endocarditis in chronic variety Bioterrorist threat?
  18. 18.  Low or normal WBC count; in the late stages there is leucocytosis Anemia, thrombocytopenia and elevated serum transaminases Hyponatremia CSF analysis is usually normal; rarely mononuclear plecytosis (<300 cells/micro L)
  19. 19.  Serological evidence of infection usually not occur earlier than second week of illness.
  20. 20.  Gold standard test IgM titre >1:64 IgG titres >1:64 but <1:125 suggests previous infection A single titer is neither sensitive (patients can die before seroconversion) nor specific (an elevated titer can represent prior infection) ELISA – available in India and is the preferred diagnosis at present
  21. 21.  Slide agglutination test Tests the presence of antigenic cross- reactivity between Rickettsia spp. and certain serotypes of non-motile Proteus spp., suffers from poor sensitivity and specificity, with a recent study showing an overall sensitivity as low as 33% and specificity of 46%.
  22. 22. Rickettsia Agent AntigenSpotted Fever Group OX 2 (Pr.vulgaris)Typhus Group, RMSF OX 19 (Pr.vulgaris)Scrub typhus OX K (Pr.mirabilis)
  23. 23.  Complement fixation Latex agglutination Microagglutination Immunoperoxidase assay
  24. 24.  Drug of choice for all ages – Doxycycline(4 mg/kg/day divided every 12 hr PO or IV, maximum 200 mg/day) Chloramphenicol – Allergy to Doxycycline, Pregnant women (50-100 mg/kg/day divided 6th hourly, max 3 g/day) Continued for minimum of 5-7 days and for atleast 3 days until patient is afebrile.
  25. 25.  Azithromycin, Clarithromycin Fluoroquinolones Rifampicin -Found to be more effective in typhus groups.
  26. 26.  Patient coming from endemic area. H/O contact-pets/ h/o tick bite. Classical triad Rash without coryza. hepatosplenomegaly,edema,gangrene,anemia,thrombocyto penia Fever,rash,altered sensorium, convulsions PUO and not responding to routine antibiotics
  27. 27.  When applied to the patients presenting with fever of unknown source, a clinical score of 14 or more on the proposed scoring system has very high sensitivity and specificity for the diagnosis of spotted fever group of rickettsial diseases.