James A. Higgins

Molecular identification of rickettsia-like microorganisms associated with colonized cat fleas (Ctenocephalides felis)

Cat fleas (Ctenocephalides felis) from eight commercial flea colonies from various regions of the USA were examined by selective PCR amplification, and subsequent restriction digest analysis and Southern hybridization of PCR products, for the presence of a rickettsia‐like organism (ELB agent). These flea colonies were either started with fleas from one supplier (EL Labs), in which ELB agent was first identified, or were started with fleas from stray cats and dogs and later came into contact with ELB‐infected fleas. Infection rates in the colonies ranged from 43% to 93%. The successful propagation of ELB agent in these colonies may be due to efficient trans‐stadial and transovaria) transmission. While ELB agent has recently been identified in blood from human murine typhus cases, attempts to infect mammalian cells and SCID mice with flea isolates were unsuccessful.

In vitro and in vivo antibiotic susceptibilities of ELB rickettsiae.

The activities of doxycycline, rifampin, chloramphenicol, and erythromycin against ELB rickettsiae (Rickettsia azadi) were determined by dye uptake and plaque assays. Plaque formation in Vero cells was inhibited by 0.12 microgram of doxycycline per ml. The data presented demonstrate the susceptibility of ELB rickettsiae to commonly used antibiotics for the treatment of rickettsial diseases.