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Table II.

Selected phenotypic differences between the insect and selected tick borne rickettsiae.

Rickettsial species R. prowazekii R. typhi R. felis R. rickettsii R. conorii
Intranuclear growth No No No Yes Yes
Hemolytic activity Yes Yes Yes No No
Culture attributes:
plaque size (Vero) Small Small Large Large Large
Early escape before host cell death No Yes Yes Yes Yes
Escape via actin polymerization-derived motility (RickA) No No Yes Yes Yes
Persistence in humans or mammalian hostsa Yes Yes NR No (?) No
Maintenance in vectorb TST only TST;TOT TST;TOT TST; TOT TST;TOT
Major route of transmission to humans Louse feces Flea feces Flea bite Tick bite Tick bite
Plasmid(s) No No Yes No No
Type IV Pili No No Yes No No
Disease in humans:
Eschar No No Yes/No Rare Yes
Rash Yes Yes Yes/No Yes Yes
Fever Yes Yes Yes Yes Yes
Mortality Ratec High Low NR High Mild

NR = none reported; ? = Only one instance of R. rickettsii being recovered from a lymph node that was excised one year after the patient treatment and resolution of RMSF [30]. However, despite this exceptional case we are not aware of any instances of recrudescent RMSF like we have seen in Brill-Zinsser disease.


TST = transstadial transmission; TOT = transovarial transmission.


From reference 39 (mortality rate: > 15% high; 2–7% mild/moderate; < 1% low). Note: since fleas and ticks in reality do not “bite”, rickettsiae are released into the host’s skins during the tick probing and feeding.