2. Rickettsiae:
• parasitic bacteria
• Obligate intracellular parasite
• Bigger than virus
• Smaller than bacteria
• Carried by host arthropods
• Invade human mononuclear cells, neutrophils, bld
vessel endotheliums
3. Pathology
• Rickettsia are transmitted to humans by the bite of
infected arthropod vector
• Multiply at the site of entry and enter the blood
stream
• Widespread vasculitis and endothelial
proliferation affect organs
• Thrombotic occlusion gangrene
4. • Travellers/ inhabitants of endemic areas likely have
septicemia but (-)cultures ?Typhus
• Incubation period: 2 -23 days
5. Signs
Mild/ asymptomatic
Severe/ systemic: sudden fever, frontal
headache, confusion & jaundice
Eschar: dark crusty ulcer at the site of a bite
Rickettsial rash: macular, papular, petechial or
hemorrhagic
7. Epidemic typhus
• R. prowazeki
• Spread: human lice Pediculus humanus corporis
• Brill Zinnser Disease
• Rash: truncal, then peripheral
• Incubation period: 5 – 21 days
8. Rocky Mountain Spotted
Fever
• R. rickettsii
• Tick- borne
• Most serious form
• Incubation period – 1 week
• Rash begins as macules on hands/feet
Spreading, becoming petechial or hemorrhagic
• More similar to typhus fever but the rash appears
earlier and is more prominent.
9. Tick Typhus
• R. conorri
• Boutonneuse fever
• Rash starts in axilla
• Becoming purpuric as it spreads
• Conjunctival suffusion
• Jaundice, deranged
clotting, meningoencephalitis, renal
failure, cerebritis
10. Scrub typhus
• Oriental tsutsugamushi
• Most common in SE Asia
• Signs:
• Eschar from chigger bite
• Hepatomegaly, cough, lymphadenopathy, tachyp
nea, abdominal
pain, constipation, edema, splenomegaly, vomiting
, rash, petechiae, sudden deafness,
12. Murine Endemic Typhus
• R. typhi
• Spread: fleas from rats (Xenopsylla cheopis)
• Reservoir: Rat
• to humans
• Prevalent in warm coastal ports
13. Diagnosis
• clinical history
• physical exam
• tests based on identification of the bacterial genus
and species by PCR testing of skin biopsy of skin
rash, skin lesions/blood samples
• immunohistological staining that identifies the
bacteria within infected tissue (skin tissue, usually)
• Dx late or after the disease has been treated with
antibiotics, when significant titers of antirickettsial
antibodies are detected by immunological
techniques.
14. Diagnosis
• CBC: show anemia and low platelets
• High level of typhus antibodies
• Low level of albumin
• Low sodium level
• Mild kidney failure
• Mildly high liver enzymes
15. ISOLATION
• Blood is inoculated in guinea pigs/mice.
• Observed on 3rd – 4th week.
• Animal responds to different rickettsial species can
vary
• Symptoms:
• Rise in temperature – all species.
• Scrotal inflammation,swelling,necrosis –
R.typhi, R.conori, R.akari ( except R.prowazekii)
16. Serology
• Reliable test to confirm rickettsial diseases
• Antibody detection by Weil-felix test
• Antigen detection by IFA
17. WEIL-FELIX TEST
• Heterophile agglutination test using
• non motile proteus strains (OX 19, OX 2, OX K)
• to find rickettsial antibodies in patient’s serum.
• Procedure:
• Serum is diluted in three separate series of tubes
followed by the addition of equal amount of
OX19,OX2,OXK in 3 separate series of tubes.
• Incubation at 370C for overnight.
• Observe for agglutination
18. WEIL-FELIX TEST
• Strong Agglutination with OX 19 – means epidemic
& endemic typhus.
• Strong agglutination with OX 19 & OX 2 –
• means Spotted fever
• Strong agglutination with OX K – Scrub typhus
• (Scrub typhus by Orientia tsutsugamushi
• (one of the rickettsial disease)
22. Treatment
• Doxycycline 100mg/ 12hrs PO/IV for 7 days or
48 hours after temp is normal
• Chloramphenicol 500mg/ 6 hours PO for 10-14 days
• Azithromycin 500 mg 1 dose for tick & Scrub typhus
