Rickettsial infections

2. Geographical distribution in India
 Sub – himalyan belt -Jammu and Kashmir –
nagaland, Himachal Pradesh,
Uttaranchal, Rajasthan, Assam, West
Bengal, Maharashtra,
Kerala, Tamil Nadu and Delhi

3. Rickettsia
Gram-negative
bacilli
obligate
intracellular.

4. Groups
 Spotted fever group
Typhus group
 Scrub typhus
 Ehrlichioses and anaplasmosis
 Q fever

5. Arthropod vector
Tick
Except:
Epidemic typhus -
louse
Rickettsial pox – mite
Scrub typhus –chigger
Q fever – aeresol
inhalation ( no vector)

6. Host
 Dogs
Rodents
Except:
Epidemic typhus
- humans
Q fever - cattle,
goats, cats

7. Pathogenesis
Bite
Blood stream
Endothelium/vascular smooth muscles
Target cells
 Host defenses – T cell, TNF α, γ interferon

8. History
Removal of an attached tick ( 60%)
 Endemic area/ wooded area
 Season – July to October
 Similar illness in close contacts
Contact with dog

9. Clinical features
Incubation period – 2 – 14 day
Common symptoms:
Clinical triad
 Fever
 Rash - centripetal
Headache

10. Rash
Early stage:
Discrete, pale, rose red,
blanching maculopapular
on extremities
Late stage:
Petechial /haemorragic /
purpuric/Ecchymosies/
necrotic/ulcer

11. Eschar
red induration
Enlarge
Vesiculates
Ruptures
Eschar
3 – 4 wks
Resolves

12. Others symptoms:
 Lympadenopathy
 Hepatospleenomegaly
 Edema
 Conjunctival congestion
 Gastrointestinal symptoms – emesis, pain
 CNS involvement
 Pulmonary infiltrates – Q fever
 Infectious mononucleosis like syndrome - ehrelichia

13. Complication
 CNS - Cerebral edema, Meningoencephalitis
Neurologic sequelae,
 RS -Noncardiogenic pulmonary edema,
consolidation
CVS - vascular collapse, Myocarditis
RENAL - acute renal failure
 LIVER - Hepatic dysfunction
Multiorgan damage

14. Fulminant RMSF
Death< 5 days
G6PD deficiency individuals
DIC
Liver/ renal/ respiratory failure

15. Common lab abnormalities
 Increased AST and ALT
 Decreased platelets
 Decreased Na (+/-)
 Decreased WBC (+/-), left shift
 Interstital infiltrate ( Qfever)
 Atypical lymphocytosis (sennetsu
ehirlichiosis)

16. Diagnostic tests
Early
Immunohistochemistry of skin biopsy
 Direct fluorescent antibody test
PCR
After 1 wk
 Indirect fluorescent antibody test – Gold
standard
4 fold increase/ titre of >64

17. Other investigations
Immunoperoxidase assay
 Lattex agglutination test
 Indirect haemagglutination test
 ELISA
 Dot – blot immunoassay
Weil – Felix – high specific/low sensitive

18. Treatment
Doxycycline (2.2 mg/kg/dose bid PO or IV,
maximum 200 mg/day) - DOC
Tetracycline (25–50 mg/kg/day divided
every 6 hr PO, maximum 2 g/day)
 Chloramphenicol (50–100 mg/kg/day
divided every 6 hr IV, maximum 3 g/day)

19.  Azithromycin – doxycycline resistant
 Clarithromycin
 Fluroquinolones
Trimethoprim – sulfamethoxazole
 Rifampicin – scrub typhus