Abstract
Based on limited serological studies, at least 10% of the US population has been exposed to spotted fever group Rickettsia (SFGR) species. The immunofluorescence antibody assay (IFA) has been the gold standard for the serodiagnosis of rickettsial infections such as spotted fever rickettsiosis (SFR). However, the IFA is semi-quantitative and subjective, requiring a high level of expertise to interpret it correctly. Here, we developed an enzyme-linked immunosorbent assay (ELISA) for the serodiagnosis of Rickettsia parkeri infection in the guinea pig. Our ELISA is an objective, quantitative, and high-throughput assay that shows greater sensitivity and resolution in observed titers than the IFA. We methodically optimized relevant parameters in sequence for optimal signal-to-noise ratio and low coefficient of variation% values. We used a guinea pig model as it is a part of our overall research efforts to understand the immunological and clinical response to SFGR species after tick transmission. Guinea pigs are a useful model to study SFR and show clinical signs of SFR, such as fever and eschars. We anticipate that this assay will be easily adapted to other hosts, including humans and other SFGR species.
Highlights
Published: 20 January 2021Rickettsiae are obligate intracellular, Gram-negative bacteria associated with various arthropod vectors such as ticks, fleas, and mites [1,2]
To overcome the shortcomings of the immunofluorescence antibody assay (IFA), we developed an enzyme-linked immunosorbent assay (ELISA) for spotted fever rickettsiosis (SFR) diagnosis as the ELISA is objective, quantitative, has higher throughput, and is more sensitive compared to the IFA
We addressed the need for an improved method of identifying spotted fever group Rickettsia (SFGR) exposure using the guinea pig model for SFR
Summary
Rickettsiae are obligate intracellular, Gram-negative bacteria associated with various arthropod vectors such as ticks, fleas, and mites [1,2]. Rickettsia parkeri is an emerging pathogenic SFGR species and agent of SFR; it is primarily transmitted via Amblyomma maculatum (Gulf Coast tick) in the southern USA [4]. In a study of human exposure to four SFGR, R. rickettsii, R. parkeri, R. amblyommatis, and R. montanensis, all samples tested were cross-reactive to at least two SFGR species, with a minimum antibody titer of 64 [12]. Based on published seroprevalence data to date, humans are at risk of exposure to more than one agent of SFR and can develop antibodies to both pathogenic and non-pathogenic SFGR species. Beginning in the late 1980s, the guinea pig was mostly replaced by the mouse model for SFR and other infectious diseases This new preference in models was primarily driven by the widespread availability of genetically modified murine models and mouse-specific reagents [15]. As serologic assays are more useful for epidemiologic studies, an improved assay remains critical to assess population exposure and make informed public health decisions
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