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Published on: May 19, 2020
Rapid Capsular Antigen Immunoassay for Diagnosis of Inhalational Anthrax: Preclinical Studies and Evaluation in a
Marcellene A Gates-Hollingsworth1, Cari B Kolton2, Alex R Hoffmaster2
1Department of Microbiology and Immunology, University of Nevada, Reno School of Medicine, Reno, Nevada, USA.
Abstract:
Inhalational anthrax is a fatal infectious disease. Rapid and effective treatment is critically dependent on early and accurate diagnosis. Blood culture followed by identification and confirmation may take days to provide clinically relevant information. In contrast, immunoassay for a shed antigen, the capsular polypeptide gamma-d-polyglutamate (γDPGA), can provide rapid results at the point of care. In this study, a lateral flow immunoassay for γDPGA was evaluated in a robust nonhuman primate model of inhalational anthrax. The results showed that the time to a positive result with the rapid test using either serum or blood as a clinical specimen was similar to the time after infection when a blood culture became positive. In vitro testing showed that the test was equally sensitive with cultures of the three major clades of Bacillus anthracis. Cultures from other Bacillus spp. that are known to produce γDPGA also produced positive results. The test was negative with human sera from 200 normal subjects and 45 subjects with culture-confirmed nonanthrax bacterial or fungal sepsis. Taken together, the results showed that immunoassay for γDPGA is an effective surrogate for blood culture in a relevant cynomolgus monkey model of inhalational anthrax. The test would be a valuable aid in early diagnosis of anthrax, which is critical for rapid intervention and a positive outcome. Use of the test could facilitate triage of patients with signs and symptoms of anthrax in a mass-exposure incident and in low-resource settings where laboratory resources are not readily available. IMPORTANCE Patient outcome in anthrax is critically dependent on early diagnosis followed by effective treatment. We describe a rapid lateral flow immunoassay that detects capsular antigen of Bacillus anthracis that is shed into blood during infection. The test was evaluated in a robust cynomolgus monkey model of inhalational anthrax. Rapid detection of capsular antigen is an effective surrogate for the time-consuming and laboratory-intensive diagnosis by blood culture, direct fluorescent antibody staining, or other molecular testing. The test can be performed at the point of patient contact, is rapid and inexpensive, and can be used by individuals with minimal training.
Insights
A new rapid immunoassay detects gamma-d-polyglutamate (γDPGA), a Bacillus anthracis antigen, for early inhalational anthrax diagnosis. This test offers a faster alternative to blood cultures, improving patient outcomes and aiding in mass-exposure triage.
Area of Science:
- Microbiology and Infectious Diseases
- Immunodiagnostics
- Biodefense and Public Health
Background:
- Inhalational anthrax is a severe, often fatal disease requiring prompt diagnosis for effective treatment.
- Current diagnostic methods like blood cultures are time-consuming, delaying critical clinical intervention.
- Early detection of Bacillus anthracis infection is paramount for improving patient prognosis and managing outbreaks.
Purpose of the Study:
- To evaluate a novel lateral flow immunoassay for the rapid detection of gamma-d-polyglutamate (γDPGA), a key antigen shed by Bacillus anthracis.
- To assess the immunoassay's performance as a point-of-care diagnostic tool in a nonhuman primate model of inhalational anthrax.
- To determine if the immunoassay can serve as a rapid surrogate for traditional, laboratory-intensive diagnostic methods.
Main Methods:
- A lateral flow immunoassay targeting the capsular polypeptide γDPGA was developed and tested.
- The assay was evaluated using serum and blood specimens from a cynomolgus monkey model of inhalational anthrax.
- Specificity was confirmed using sera from healthy individuals and patients with non-anthrax sepsis; sensitivity was tested against various Bacillus anthracis clades and other Bacillus species.
Main Results:
- The rapid immunoassay provided positive results in a timeframe comparable to the positivity of blood cultures post-infection.
- The test demonstrated equal sensitivity across major Bacillus anthracis clades and cross-reactivity with other γDPGA-producing Bacillus species.
- The immunoassay showed high specificity, yielding negative results in healthy subjects and patients with non-anthrax bacterial or fungal sepsis.
Conclusions:
- The γDPGA lateral flow immunoassay is an effective and rapid surrogate for blood culture in diagnosing inhalational anthrax.
- This point-of-care test can significantly aid in early anthrax diagnosis, facilitating timely treatment and improving patient outcomes.
- The assay's speed, low cost, and ease of use make it valuable for mass-exposure incidents and resource-limited settings.
