Rabies laboratory tests

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Iqra Qamar M.D.[2]

Overview

Routine lab findings are non-specific and may include peripheral leukocytosis, respiratory alkalosis followed by respiratory acidosis, albuminuria, and pyuria. The lumbar puncture may show lymphocytic pleocytosis, CSF protein-elevation, and normal glucose concentration. Serology is useful in assessing the serostatus in immunized humans and animals as it is difficult to document the neutralizing antibody response via immunofluorescence because mostly death occurs prior to mounting a response. Serologic tests include reverse transcriptase polymerase chain reaction (RT-PCR), viral culture, immunofluorescence staining, indirect immunofluorescence, direct fluorescent antibody test (dFA) and virus neutralization assays.

Laboratory Findings

Routine lab findings are non-specific

Serology

In order to make a lab diagnosis of rabies, certain specimens need to be taken from the body and specific tests done are as follows:

Sample Sensitivity Specificity Test Significance/Interpretation
Saliva 63.2 70.2 Reverse transcriptase polymerase chain reaction (RT-PCR) Detects viral RNA
Viral culture Isolates the virus
Skin biopsy 98 98.3 Reverse transcriptase polymerase chain reaction (RT-PCR) Detects viral RNA
Immunofluorescence staining Detects viral antigen
Serum low low Indirect immunofluorescence Detects viral antigen
Virus neutralization assays Detects antibody response
Cerebrospinal fluid low low Indirect immunofluorescence Detects viral antigen
Virus neutralization assays Detects antibody response

Direct Fluorescent Antibody Test (dFA)

The dFA test is based on the observation that animals infected by rabies virus have rabies virus proteins (antigen) present in their tissues. Because rabies is present in nervous tissue (and not blood like many other viruses), the ideal tissue to test for rabies antigen is brain. The most important part of a dFA test is flouresecently-labeled anti-rabies antibody. When the labeled antibody is incubated with rabies-suspect brain tissue, it will bind to rabies antigen. Unbound antibody can be washed away and areas, where the antigen is present, can be visualized as fluorescent-apple-green areas using a fluorescence microscope. If rabies virus is absent there will be no staining.

The image with the bright green spots displays a positive test for rabies and the image below it, with no spots, displays a negative test for rabies.

The rabies antibody used for the dFA test is primarily directed against the nucleoprotein (antigen) of the virus. Rabies virus replicates in the cytoplasm of cells, and infected cells may contain large round or oval inclusions containing collections of nucleoprotein (N) or smaller collections of antigen that appear as dust-like fluorescent particles if stained by the dFA procedure.

References

  1. Manning SE, Rupprecht CE, Fishbein D, Hanlon CA, Lumlertdacha B, Guerra M, Meltzer MI, Dhankhar P, Vaidya SA, Jenkins SR, Sun B, Hull HF (2008). "Human rabies prevention--United States, 2008: recommendations of the Advisory Committee on Immunization Practices". MMWR Recomm Rep. 57 (RR-3): 1–28. PMID 18496505.
  2. Noah DL, Drenzek CL, Smith JS, Krebs JW, Orciari L, Shaddock J, Sanderlin D, Whitfield S, Fekadu M, Olson JG, Rupprecht CE, Childs JE (1998). "Epidemiology of human rabies in the United States, 1980 to 1996". Ann. Intern. Med. 128 (11): 922–30. PMID 9634432.
  3. Warrell MJ, Warrell DA (2004). "Rabies and other lyssavirus diseases". Lancet. 363 (9413): 959–69. doi:10.1016/S0140-6736(04)15792-9. PMID 15043965.

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