Transmission mechanisms of an emerging insect-borne rickettsial pathogen

Abstract

BackgroundVector-borne pathogens must overcome arthropod infection and escape barriers (e.g. midgut and salivary glands) during the extrinsic incubation period (EIP) before subsequent transmission to another host. This particular timespan is undetermined for the etiological agent of flea-borne spotted fever (Rickettsia felis). Artificial acquisition of R. felis by blood-feeding cat fleas revealed dissemination to the salivary glands after seven days; however, this length of time is inconsistent with co-feeding studies that produced infectious cat fleas within 24 h of infection. In the current study, we demonstrated that an alternative mechanism is responsible for the early-phase transmission that typifies flea-borne R. felis spread.MethodsCo-feeding transmission bioassays were constructed to assess temporal dynamics of R. felis amongst cat fleas, including exposure time to produce infectious fleas and association time to transmit infection to naïve fleas. Additional experiments examined the proportion of R. felis-exposed cat fleas with contaminated mouthparts, as well as the likelihood for cat fleas to release R. felis from their mouthparts following exposure to an infectious bloodmeal. The potential for mechanical transmission of R. felis by co-feeding cat fleas was further examined using fluorescent latex beads, as opposed to a live pathogen, which would not require a biological mechanism to achieve transmission.ResultsAnalyses revealed that R. felis-infected cat fleas were infectious to naïve fleas less than 24 h after exposure to the pathogen, but showed no rickettsial dissemination to the salivary glands during this early-phase transmission. Additionally, the current study revealed that R. felis-infected cat fleas must co-feed with naïve fleas for more than 12 h in order for early-phase transmission to occur. Further evidence supported that contaminated flea mouthparts may be the source of the bacteria transmitted early, and demonstrated that R. felis is released from the mouthparts during brief probing events. Moreover, the use of fluorescent latex beads supports the notion that early-phase transmission of R. felis is a mechanical mechanism.ConclusionsDetermination of the transmission mechanisms utilized by R. felis is essential to fully understand the vulnerability of susceptible vertebrate hosts, including humans, to this pathogen.

Infectious blood source alters early foregut infection and regurgitative transmission of Yersinia pestis by rodent fleas

“…EPT of Y . pestis was long assumed to be an example of mechanical transmission, and EPT of Rickettsia felis by cat fleas occurs by this mechanism [ 41 ]. However, the fact that different fleas vary greatly in their EPT efficiency following infection with Y .…”

History, Rats, Fleas, and Opossums: The Ascendency of Flea-Borne Typhus in the United States, 1910–1944

“…By the end of 1931, Ceder, Dyer, Rumreich, and Badger demonstrated that feces from infected fleas were capable of transmitting FBT through scratches on the skin of guinea pigs, indicating that a major route of transmission is through inoculation of infected feces into abraded skin or mucous membranes [50,119] (subsequently, it was shown that a flea bite may also transmit the infection [2,39]). In the following year, the same team discovered that the feces of X. cheopis become highly infectious six days after feeding on R. typhi-infected rats.…”

“…Flea-borne typhus (FBT), also known as murine typhus, is an infection caused by Rickettsia typhi and R. felis. The infection is transmitted to humans by the inoculation of a bite site, a skin abrasion, or mucous membranes with feces from fleas infected with these rickettsiae or by a flea bite [1,2]. Flea-borne typhus is the most prevalent and widely distributed rickettsial infection [1,3].…”

Suspected and Confirmed Vector-Borne Rickettsioses of North America Associated with Human Diseases

“…It is suspected that C. felis acquire the organism by feeding on a R. felis infected host, such as a cat or opossum but this step of the transmission cycle has yet to be confirmed. Cat fleas are able to maintain the infection through at least 12 generations without feeding on another rickettsemic host [ 86 ], suggesting that transmission among C. felis could be through co-feeding [ 87 ] or mating [ 9 ].…”