Section 4 of the WHO Expert Consultation on Rabies :
http://apps.who.int/iris/bitstream/10665/85346/1/9789240690943_eng.pdf
Chapter 2.1.13 of the OIE Terrestrial Manual (Rabies) :
http://www.oie.int/fileadmin/Home/eng/Health_standards/tahm/2.01.13_RABIES.pdf
CDC guidance on Rabies Diagnosis :
www.cdc.gov/rabies/diagnosis/index.html