1. RICKETTSIA This is a bacterial genus. @ It resembles viruses in:
Obligate parasites (live inside the cell).
b) Same size as the largest virus.

3. @ It is different from viruses in:
a) Contains both DNA & RNA.
b) Multiplies by binary fission.
c) Transmitted by lice, fleas, mites,
and ticks
d) Possesses enzymes.
e) Sensitive to antiseptics and antibiotics.

5. Rickettsia has 3 groups:
SPECIES:
Rickettsia has 3 groups:
1- Typhus group, contains the species:
a) R. prowazeki.
b) R. typhi.
2- Scrub typhus group, contains the species:
a) R. tsutsugamushi.
3- Spotted fever group, contains the species:
a) R. conori
b) R. conori pijperi
c) R. siberica
d) R. rickettsi

7. NORMAL HABITAT & TRANSMISSION
@ R. prowazeki: host is Man. Man is
infected by the body louse.
@ R. typhi: host is rats. Man is infected
by the rat flea

9. @ R. rickettsi: host is dogs, and rodents.
Man is infected by ticks.
@ R. tsutsugamushi: host is rat. Man is
infected by the bite of a mite.
@ R. conori & R. siberica: host is dogs &
rodents. Man is infected by ticks.

11. Diseases: @ R. prowazeki: causes louse-borne typhus (epidemic typhus).
@ R.typhi: causes flea-borne typhus
(endemic typhus).
@ R. tsutsugamushi: causes mite-borne
typhus (scrub typhus).
@ R. conori & R. conori pijperi: cause
tick-borne typhus.

13. @ R. siberica: causes Indian tick typhus
fever.
@ R. rickettsi: causes Rocky Mountain
spotted fever.

15. Laboratory Diagnosis * Microscopy:
@ Rickettsiae occur as cocci or rods. In
tissues they are stained by Giemsa,
Macchiavello, or Castaneda stains.
* Culture:
@ Cultured in chick-embryo.

17. Serology: 3 tests:
Indirect fluorescent antibody (IFA)
test: Very reliable. Used in detecting acute infections.
2. CFT: Not very sensitive.
3. Weil-Felix reaction: Depends on cross
reactivity between antibodies of
Rickettsia and antibodies of:
# Proteus vulgaris: strains OX19 & OX2
# Proteus mirabilis: strain OXK.

19. Weil-Felix Test:
@ In louse-borne & flea-borne typhus:
Antibodies rise after 3rd week after
infection
@ False negative results occur in
infections of R. tsutsugamushi.
@ False positive results occur with
Proteus, relapsing fever, brucellosis,
and infectious mononucleosis infections

21. Immunity:
@ First IgM antibodies appears, then
followed by IgG which persists in
serum for many years.
@ Infection with louse-borne typhus and
spotted fever give immunity for 1 year
then reinfection may occur.
@ Reinfection in scrub typhus is rare.