Direct fluorescent antibody

CDC Case Definition Laboratory criteria for diagnosis is (1) a positive direct fluorescent antibody test (preferably performed on central nervous system tissue) or (2) isolation of rabies virus (in cell culture or in a laboratory animal). 

Rapid antigen and point-of-care tests, direct fluorescence antibody test, and the reverse-transcription polymerase chain reaction assay may be used for rapid detection of virus. 

Because T. pallidum is difficult to culture in vitro, diagnosis is based primarily on dark-held or direct fluorescent antibody microscopic examination of serous material from a suspected syphilitic lesion or on results from serologic testing. 

Tests that allow rapid identification of chlamydial antigens in genital secretions are the direct fluorescent antibody test, the enzyme immunoassay (requires just 30 minutes for results), the DNA hybridization probe and nucleic acid amplification tests. 

Direct fluorescent antibody smears have become a more efficient method than Giemsa stains or tissue cultures fiar identifying chlamydia. Commercially prepared kits make specimen collection convenient, and results are available in approximately 24 hours. Good results, however, depend on obtaining an adequate specimen. Fluorescein-labeled monoclonal antibodies in the staining reagent specific for Chlamydia trachomatis outer membrane proteins bind to the C. trachomatis in the smear. Studies that compare direct fluorescein antibody techniques with tissue culture results have found acceptable sensitivity and specificity values. 

Diagnosis and Treatment Skin anthrax may be diagnosed from the biopsy of the sore and performing microscopic examination of the organism. Inhalation anthrax however, is difficult to diagnose. Chest x-ray, lab cultures and blood tests should be carried out. Rapid laboratory tests may be carried out to diagnose anthrax. Such tests include polymerase chain reaction (PCR), enzyme-linked immunosorbent assay (ELISA) and direct fluorescent antibody (DFA) methods. 

Fig. 23-13. These Yersinia pestis fluorescent cells are from infected mouse spleen. Notice how the outlines of the coccobacilli light up in this direct fluorescent antibody (DFA) test. The DFA test is specific and therefore better than the other stains discussed in this chapter (original magnification x 1,000). Photograph Courtesy of M. C. Chu, Centers for Disease Control and Prevention, Fort Collins, Colo.

Obtain a Gram stain of blood, CSF, lymph node, or sputum. Other diagnostic tests Include direct fluorescent antibody testing and PCR for antigen detection. 

Obtain blood and sputum cultures. F tularensis may be identified by direct examination of secretions, exudates, or biopsy specimens using direct fluorescent antibody or immunohistochemical stains. Serology may retrospectively confirm the diagnosis. 

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