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Clinical and Diagnostic Laboratory Immunology, March 2001, p. 409-414, Vol. 8, No. 2
Infectious Diseases Directorate, Naval
Medical Research Center,1 and Uniformed
Services University of the Health Sciences,2
Bethesda, Maryland, and PanBio Pty Ltd., Queensland,
Australia3
Received 3 July 2000/Returned for modification 19 October
2000/Accepted 9 January 2001
The variable 56-kDa major outer membrane protein of Orientia
tsutsugamushi is the immunodominant antigen in human scrub
typhus infections. We developed a rapid immunochromatographic flow
assay (RFA) for the detection of immunoglobulin M (IgM) and IgG
antibodies to O. tsutsugamushi. The RFA employs a
truncated recombinant 56-kDa protein from the Karp strain as the
antigen. The performance of the RFA was evaluated with a panel of
321 sera (serial bleedings of 85 individuals suspected of scrub typhus)
which were collected in the Pescadore Islands,
Taiwan, from 1976 to 1977. Among these 85 individuals, IgM tests were
negative for 7 cases by both RFA and indirect fluorescence assay (IFA)
using Karp whole-cell antigen. In 29 cases specific responses were
detected by the RFA earlier than by IFA, 44 cases had the same
detection time, and 5 cases were detected earlier by IFA than by RFA.
For IgG responses, 4 individuals were negative with both methods, 37 cases exhibited earlier detection by RFA than IFA, 42 cases were
detected at the same time, and 2 cases were detected earlier by IFA
than by RFA. The sensitivities of RFA detection of antibody in sera
from confirmed cases were 74 and 86% for IgM and IgG, respectively.
When IgM and IgG results were combined, the sensitivity was 89%. A
panel of 78 individual sera collected from patients with no evidence of
scrub typhus was used to evaluate the specificity of the RFA. The
specificities of the RFA were 99% for IgM and 97% for IgG. The
sensitivities of IFA were 53 and 73% for IgM and IgG, respectively, and were 78% when the results of IgM and IgG were combined. The RFA
test was significantly better than the IFA test for the early detection of antibody to scrub typhus in primary
infections, while both tests were equally sensitive with reinfected individuals.
1071-412X/01/$04.00+0 DOI: 10.1128/CDLI.8.2.409-414.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Early Diagnosis of Scrub Typhus with a Rapid Flow Assay Using
Recombinant Major Outer Membrane Protein Antigen (r56) of
Orientia tsutsugamushi
and
*
Corresponding author. Mailing address: Viral and
Rickettsial Diseases Department, Infectious Diseases Directorate, Code
41, Naval Medical Research Center, 503 Robert Grant Ave., Silver
Spring, MD 20910-7500. Phone: (301) 319-7438. Fax: (301)
319-7460. E-mail: Chingw{at}nmrc.navy.mil.
Present address: Viral and Rickettsial Zoonoses Branch, Centers for
Disease Control and Prevention, Atlanta, GA 30333.
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