Honors College Theses

Publication Date

2025

Major

Public Health (B.S.)

Release Option

Restricted to Georgia Southern

Faculty Mentor

Marina Eremeeva

Abstract

Tick-borne disease cases have been steadily rising throughout the years. Spotted fever group rickettsioses (SFGR) caused by a diverse group of Rickettsia pathogens contributed to this upward trend globally and nationally. Despite this, relatively little is known about the extent of exposure to tick-borne pathogens in Georgia, USA. In this rural state, Amblyomma americanum, the Lone Star tick, is common. It is frequently infected with Rickettsia amblyommatis, which is thought to be avirulent. This study aimed to determine if exposure to R. amblyommatis accounts for most of the human antibody responses detected by SFGR serologic tests in Georgia. The indirect microimmunofluorescence assay (IFA) was utilized to determine the end-point titers of IgG-type antibodies reacting with the cell culture-grown antigen of Rickettsia rickettsii. Highly positive sera (IFA titer > 256) were tested by western blotting to determine their reactivity with antigens of R. rickettsii, R. amblyommatis, and R. parkeri. One hundred-two sera tested IFA- positive with the antigen of R. rickettsii, a known human pathogen. Among them, 78% of sera had an IgG-antibody titer of 1/256 < (CDC positivity cutoff 1/64). 103 sera tested IFA-positive with R. amblyommatis antigen; 81% of sera had an IgG-antibody titer of 1/256 <;. By Western blotting (WB), 18 sera reacted only with Rickettsia surface protein antigens (SPA), 57 reacted with SPA, lipopolysaccharide, and/or other Rickettsia antigens, while 3 sera had non-specific reactivity. Several sera were also tested with R. parkeri, and all were reactive with SPA. WB cross-absorption experiments indicated that R. amblyommatis was the source of exposure for individuals tested.

Thesis Summary

The purpose of this study is to determine if Rickettsia amblyommatis (a lesser pathogenic Rickettsia) or another Rickettsia is responsible for antibodies against spotted fever group rickettsiae of healthy individuals in Georgia, USA.

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Available for download on Monday, April 29, 2030

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