Viral Cultures and Polymerase Chain Reaction (PCR) Assay in the Workup of Rabies • Viral culture of saliva for rabies is usually positive within 2 weeks of onset of illness. • In CSF, proteins are elevated and 80% monocytosis is observed. Glucose test and spinal fluid remains normal. • Postmortem findings reveal negri bodies in the horn of ammon of cerebral cortex and hippocampus.