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The symptoms that accompany a feline calicivirus infection are usually not diagnostic alone because there are many other pathogens that can cause general upper respiratory symptoms.  However, oral ulceration and limping or joint pain are unique characteristics that may be indicative of calicivirus though it should be confirmed by other diagnostic techniques.  There are two main laboratory techniques used to diagnose feline calicivirus:

1.   Virus Isolation

This requires taking a swab of discharge from the nose, eyes, or mouth/throat of the cat.  Once the sample is obtained, the lab uses cultured cells to “grow” the virus.   Viruses must infect cells to replicate, therefore if the virus isolation test is positive for calicivirus the culture cells will become infected.  This will lead to death, or apoptosis, within the culture cells which can be recognized by trained technicians.  The disadvantage of this method is that the isolation can take a long time, and calicivirus can be tricky isolate due to the fragile and variant nature of RNA viruses.

2.   Reverse transcription-Polymerase Chain Reaction (RT-PCR)

PCR is a molecular technique used to amplify a DNA sequence.  In the case of calicivirus, which is an RNA virus, the RNA must be “reverse transcribed” into its DNA complement with the enzyme reverse transcriptase.   Once the assay is complete the DNA sequence can be used to diagnose the virus.  When this is done as a real-time RT-PCR, this test can quantify how much viral RNA there is in a particular sample.  This type of technique is also somewhat tricky due to the variety of different strains and because viral RNA can degrade quickly by enzymes in the environment.