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An Electroporation Method to Transform Rickettsia spp. with a Fluorescent Protein-Expressing Shuttle Vector in Tick Cell Lines
Published on: October 11, 2022
Transmission of Amblyomma maculatum-Associated Rickettsia spp. During Cofeeding on Cattle
Jung Keun Lee1, John V Stokes1, Gail M Moraru1
11 Department of Basic Sciences, College of Veterinary Medicine, Mississippi State University , Mississippi State, Mississippi.
Abstract:
Amblyomma maculatum is the primary vector for the spotted fever group rickettsiae, Rickettsia parkeri, a known pathogen, and "Candidatus Rickettsia andeanae," currently considered nonpathogenic. Spotted fever group rickettsiae are typically endothelial cell associated and rarely circulate in the blood. Horizontal transmission to naïve ticks through blood feeding from an infected host is likely rare. Cofeeding provides an opportunity for rickettsial transmission to naïve ticks in the absence of circulating rickettsiae. We evaluated R. parkeri transmission through cofeeding between A. maculatum adults and nymphs on beef calves. Six calves in each of two trials were infested with A. maculatum that had been capillary fed R. parkeri. Four days later, calves each received recipient A. maculatum that were either capillary fed "Ca. R. andeanae" or not capillary fed before infestation. Trials differed by whether we included a barrier to minimize adjacent feeding between recipient and donor ticks. After cofeeding, we detected R. parkeri in 27% of "Ca. R. andeanae"-free recipient ticks, whereas R. parkeri was not detected in any recipient ticks that were capillary fed "Ca. R. andeanae." Rickettsia parkeri transmission efficiency to naïve ticks was greater when ticks freely cofed in proximity. No rickettsial DNA was detected in calf blood. Results confirm cofeeding as a method of horizontal transmission of R. parkeri in the absence of host rickettsemia and suggest no evidence of transmission by cofeeding when recipient ticks are first exposed to "Ca. R. andeanae" through capillary feeding. While cofeeding may provide an opportunity for maintaining the pathogen, R. parkeri, the mechanisms driving any potential effect of "Ca. R. andeanae" on R. parkeri transmission are unclear.
Insights
Cotransmission of Rickettsia parkeri between Amblyomma maculatum ticks via cofeeding is possible without circulating bacteria in the host. However, prior exposure to "Candidatus Rickettsia andeanae" may inhibit R. parkeri transmission.
Area of Science:
- Veterinary Entomology
- Microbiology
- Infectious Diseases
Background:
- Amblyomma maculatum ticks transmit spotted fever group rickettsiae, including the pathogen Rickettsia parkeri.
- Rickettsiae are typically associated with endothelial cells and rarely found in host blood, making horizontal transmission to ticks difficult.
- Cofeeding between ticks presents a potential mechanism for rickettsial transmission in the absence of circulating bacteria.
Purpose of the Study:
- To evaluate the transmission of Rickettsia parkeri between Amblyomma maculatum ticks through cofeeding on beef calves.
- To investigate the influence of "Candidatus Rickettsia andeanae" exposure on R. parkeri transmission during cofeeding.
Main Methods:
- Two trials were conducted using beef calves infested with R. parkeri-infected Amblyomma maculatum (donor ticks).
- Recipient ticks were either exposed to "Candidatus Rickettsia andeanae" via capillary feeding or not exposed before infestation.
- Ticks were allowed to cofeed, with one trial using a barrier to limit proximity between donor and recipient ticks.
Main Results:
- Rickettsia parkeri was detected in 27% of recipient ticks not previously exposed to "Candidatus Rickettsia andeanae".
- No R. parkeri was detected in recipient ticks previously exposed to "Candidatus Rickettsia andeanae".
- R. parkeri transmission efficiency was higher when ticks freely cofed in close proximity; no rickettsial DNA was found in calf blood.
Conclusions:
- Cofeeding facilitates horizontal transmission of R. parkeri between Amblyomma maculatum ticks, even without host rickettsemia.
- Prior capillary feeding exposure to "Candidatus Rickettsia andeanae" appears to inhibit R. parkeri transmission during cofeeding.
- The mechanisms underlying the interaction between "Candidatus Rickettsia andeanae" and R. parkeri transmission require further investigation.
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