A young male is admitted with history of altered sensorium and hydrophobia. A clinical diagnosis of rabies was made and corneal scrapings were taken. Which is the best test to confirm his diagnosis?

Diagnosis of rabies is made usually using skin biopsy from hairy skin over the nape of the neck. The rabies virus antigen is found in cutaneous nerves at the base of hair follicles. Corneal impression smears are low diagnostic yield and hence not performed. Choice A is ruled out as it used in post moem. Negri bodies are eosinophilic inclusions seen in Purkinje cells of cerebellum, pyramidal neurons of hippocampus. Choice B is ruled out as many vaccinated individuals are positive for antibodies in serum. Infact it is direct fluorescent antibody test that is used for skin biopsies and brain tissue and not indirect immunofluorescence. Choice C and D are very close choices in this question. Manson textbook of tropical diseases mentions viral culture for corneal impression smears. Real time PCR is mentioned for saliva, CSF and skin biopsy only.