A 25-year-old patient is admitted to the hospital presenting with symptoms suggestive of hydrophobia, which raises suspicion for rabies infection. The clinician decides to conduct additional diagnostic tests on the patient’s corneal scraping to confirm the diagnosis.

Which of the following tests is the most suitable and accurate for confirming the diagnosis in this patient?

Correct Answer » D Explanation

The Direct Fluorescent Antibody (DFA) test is the standard test for detecting rabies virus antigen in corneal epithelial smears, skin biopsy specimens (from the nape of the neck), and brain tissue.

In patients with suspected rabies:

• Corneal epithelial scrapings can be examined using the DFA test.
• Fluorescein-labeled antibodies bind to rabies viral antigen, producing characteristic fluorescence under a fluorescence microscope.
• The test is rapid, highly specific, and widely used for ante-mortem diagnosis.

Why Other Options Are Incorrect

A. Reverse Transcriptase Polymerase Chain Reaction (RT-PCR)

• Incorrect because although RT-PCR is highly sensitive and can detect rabies viral RNA in saliva, CSF, skin biopsy, or corneal samples, the question specifically asks for the test performed on corneal scraping to detect viral antigen.
• DFA is the classic and preferred antigen detection test for corneal smears.

B. Viral Culture

• Incorrect because rabies virus is difficult to culture, time-consuming, and is not routinely used for diagnosis.

C. Antibody Detection by Enzyme-Linked Immunosorbent Assay (ELISA)

• Incorrect because antibodies appear relatively late in the disease and may be absent in unvaccinated patients during the early phase.
• ELISA is therefore not the preferred test for early diagnosis.