text: Ticks can contract R. rickettsii by many means. First, an uninfected tick can become infected when feeding on the blood of an infected vertebrate host; such as a rabbit, during the larval or nymph stages, this mode of transmission is called transstadial transmission. Once a tick becomes infected with this pathogen, they are infected for life. Both the American Dog Tick and the Rocky Mountain Wood Tick serve as long-term reservoirs for Rickettsia rickettsii, in which the organism resides in the tick posterior diverticula of the midgut, the small intestine, and the ovaries. In addition, an infected male tick can transmit the organism to an uninfected female during mating. However, this process is unlikely to play a major role in the maintenance of R. rickettsii within a population as females infected during mating have not been observed to produce infected offspring. Infected female ticks can transmit the infection to their offspring, in a process known as transovarian passage. Notably, R. rickettsii is inefficient at infecting the ovaries of adult female ticks, resulting in a lowered rate of vertical transmission. Rickettsial colonization of the ovaries sees higher success when ticks obtain the pathogen as a larva or nymph. Reduced fecundity is also observed in ticks infected with R. rickettsii. As a result of these limitations, long-term maintenance of R. rickettsii in populations of ticks relies mainly on horizontal transmission through the exchange of bacteria during feedings of infected hosts.
  The duration of tick attachment, bacterial loads in tick saliva, and the transmission efficiency of Rickettsia are important factors underlying transmission from ticks to humans.