This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Virology Pa-2 (RNA Virus Pa-1,2 & Miscellaneous Viruses), Subject name: Microbiology
which of the following is best for ante-moem diagnosis of rabies? 
Select and explain. 
A. Anti Rabies antibodies in blood, B. Immunofluorescence of corneal impression, C. Negri body detection, D. Isolation of virus from saliva.
B: Immunofluorescence of corneal impression
Answer: B: Immunofluorescence of corneal impression 
Explanation: Option 1-Anti Rabies antibodies in blood appear late and can also be present after vaccination. So detection of antibodies in CSF is more significant. Option 2: Direct fluorescent antibody test is the ideal method of antemoem diagnosis of rabies. Samples can be: Corneal impression smear is only 30% sensitive, mainly it is positive in late stage. Biopsy of hair follicle of base of neck is more sensitive and considered as the best sample for direct fluorescent antibody (DFA) test . (But it is not given in the options above.) Hence, the answer is Immunofluorescence of corneal impression. Option 3: The brain biopsy of the dead animal is the specimen of choice for postmoem diagnosis of rabies. A B fig:-Histopathological examination of central nervous system tissue from autopsy of a decedent with suspected rabies infection,. (A)showing neuronal cytoplasmic inclusions (Negri bodies) after hematoxylin and eosin staining. (B).rabies virus antigen (red) after immunohistochemical staining Negri body detection is postmoem method of diagnosis, however it may not be detected in 20% of the cases.