Posted by Vector and Vector-borne Disease Committee
July 2, 2022
Authors: Chanida Fongsaran, Krit Jirakanwisal, Natthida Tongluan, Allison Latour, Sean Healy, Rebecca C. Christofferson, Kevin R. Macaluso
Affiliation: Vector-Borne Disease Laboratories, Department of Pathobiological Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, Louisiana, and Department of Microbiology and Immunology, College of Medicine, University of South Alabama, Mobile, Alabama, United States of America
Open access: PLoS Negl Trop Dis 16(6): e0010576. https://doi.org/10.1371/journal.pntd.0010576
Abstract. Rickettsia felis is an emerging etiological agent of rickettsioses worldwide. The cosmopolitan cat flea (Ctenocephalides felis) is the primary vector of R. felis, but R. felis has also been reported in other species of hematophagous arthropods including ticks and mosquitoes. Canines can serve as a bacteremic host to infect fleas under laboratory conditions, yet isolation of R. felis from the blood of a vertebrate host in nature has not been realized. Cofeeding transmission is an efficient mechanism for transmitting rickettsiae between infected and uninfected fleas; however, the mechanism of transmission among different orders and classes of arthropods is not known. The potential for R. felis transmission between infected fleas and tick (Dermacentor variabilis) and mosquito (Anopheles quadrimaculatus) hosts was examined via cofeeding bioassays. Donor cat fleas infected with R. felis transmitted the agent to naïve D. variabilis nymphs via cofeeding on a rat host. Subsequent transstadial transmission of R. felis from the engorged nymphs to the adult ticks was observed with reduced prevalence in adult ticks. Using an artificial host system, An. quadrimaculatus exposed to a R. felis-infected blood meal acquired rickettsiae and maintained infection over 12 days post-exposure (dpe). Similar to ticks, mosquitoes were able to acquire R. felis while cofeeding with infected cat fleas on rats, infection persisting in the mosquito for up to 3 dpe. The results indicate R. felis-infected cat fleas can transmit rickettsiae to both ticks and mosquitoes via cofeeding on a vertebrate host, thus providing a potential avenue for the diversity of R. felis-infected arthropods in nature.
Note: The epidemiology of emerging flea borne typhus transmission remains poorly understood, but is becoming an increasing public health problem in southern California [see PMVCAC]. Although R. felis may be maintained vertically in cat fleas, horizontal transmission via bacteremic mammals has not been shown. Transmission via co-feeding has been shown for arboviruses in the laboraory and is considered a mode of transmission of tick borne encephalitis virus by Ixodes ricinus. In the current study, infection by co-feeding was shown using a non-infected rodent or artificial blood meals. However, unless hosts develop a bacteremia, transmission would seem to rely on co-feeding by infected and non-infected arthropods in close proximity or by non-bacteremia transmission when feeding on small sized hosts with a small blood volume and therefore minimal pathogen dilution.