Rickettsiae are obligate intracellular bacteria that can cause diseases like Rocky Mountain spotted fever and typhus. They are transmitted through arthropod bites like ticks, mites and fleas. Common symptoms include fever, headache and rash. Diagnosis involves serologic tests detecting IgM and IgG antibodies. Doxycycline is the treatment of choice. Clinical features along with exposure history and serology can help diagnose rickettsial infections.

2.  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

4.  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

8.  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)

9.  Two of the rickettsial diseases are unique in
that humans may acquire them by direct
inhalation
 Q fever (Coxiella burnetii)
 Epidemic typhus (Rickettsia prowazekii)

10. Disease Rickettsial Agent Insect Vector Mammalian
Reservoir
Indian tick typhus R.conorii Tick Dog/Rodents
RMSF R.rickettsi Tick Dog/Rodents
Rickettsial pox R.akari Mite Mice

11. Disease Rickettsial Agent Vector Mammalian
Reservoir
Epidemic typhus R.prowazeki Louse Humans
Murine typhus R.typhi Flea Rodent
Scrub typhus R.tsusugamushi Mite Rodent

12.  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

14.  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

15.  Rocky Mountain spotted fever
 Murine (Endemic) typhus
 Epidemic typhus
 Q fever

16.  IP: 2 to 14 days
 H/o exposure to tick/ close contact with pets/
Endemic area/ similar illness in family

17.  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.

18. Fever
Headache
Rash

19. Necrotic
petechiae
Maculopapular

22.  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

23.  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 of
rats in the house support the diagnosis but
this is only reported 30% of the time.

24.  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.

25.  Usually does not affect children
 No vector is involved
 Presents as both acute or chronic forms
 Endocarditis in chronic variety
 Bioterrorist threat?

26.  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)

27.  Serological evidence of infection usually not
occur earlier than second week of illness.

28.  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

29.  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%.

30. Rickettsia Agent Antigen
Spotted Fever Group
OX 2 (Pr.vulgaris)
Typhus Group, RMSF OX 19 (Pr.vulgaris)
Scrub typhus OX K (Pr.mirabilis)

31.  Complement fixation
 Latex agglutination
 Microagglutination
 Immunoperoxidase assay

33.  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.

34.  Azithromycin, Clarithromycin
 Fluoroquinolones
 Rifampicin
-Found to be more effective in typhus groups.

35.  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

38.  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.