Theses and Dissertations


Jung Keun Lee

Issuing Body

Mississippi State University


Varela-Stokes, Andrea S.

Committee Member

Goddard, Jerome

Committee Member

Morgan, Timothy W.

Committee Member

Wills, Robert W.

Committee Member

Lopez, Job E.

Date of Degree


Document Type

Dissertation - Open Access


Veterinary Medical Science

Degree Name

Doctor of Philosophy


College of Veterinary Medicine


Veterinary Medical Science Program


Amblyomma maculatum Koch (Acari: Ixodidae) is the primary vector for Rickettsia parkeri which is a causative agent of American Boutonneuse fever. Infection rates of R. parkeri in A. maculatum populations from the United States are approximately 0-56%. The first human clinical case of Rickettsia parkeri infection was reported in 2014 and the patient presented with a febrile illness similar to Rocky Mountain spotted fever but showing milder clinical symptoms. Through 2016, approximately 40 human clinical cases of R. parkeri infection have been reported within southern United States. Amblyomma maculatum may also be infected with a rickettsia of unknown pathogenicity “Candidatus Rickettsia andeanae” which has 0-6.3% infection rates in much of the southeastern United States. However, the interaction between R. parkeri and “Ca. R. andeanae” is largely unknown. In studies presented here, we found infection rates of R. parkeri and “Ca. R. andeanae” in questing A. maculatum from Mississippi between 2013 and 2015 to be within the reported ranges for the Southeast, though higher than those previously reported for this area; levels of R. parkeri were also higher than “Ca. R. andeanae” in individual infected ticks. Using animal tickeeding trials, we found tick tissue levels of both rickettsiae to increase over time, while transovarial transmission was most successful for “Ca. R. andeanae” when present alone in ticks or co-infecting with R. parkeri. Finally, adult ticks transmitted R. parkeri to naïve coeeding ticks, and tick acquisition and survival was more efficient when coeeding ticks were in close proximity and naïve ticks uninfected with “Ca. R. andeanae.” In summary, this dissertation research filled specific gaps in our knowledge of R. parkeri-“Ca. R. andeanae” interactions in individual A. maculatum ticks and tick populations. Through this research, we have contributed to a better understanding of the human pathogen, R. parkeri, and sympatric species, “Ca. R. andeanae.” We anticipate that sharing these data with the research community will lead to a better understanding of the complexities of spotted fever rickettsiosis in the United States.