The only confirmed viral diseases of cats prior to 1957 were rabies, feline panleukopenia, and feline pneumonitis. Various research workers have described feline virus pneumonia, feline influenza, and viral encephalopathy as other viral diseases; however, with the possible exception of feline influenza, these latter three have not been confirmed. To date, the feline viral respiratory diseases include feline pneumonitis, feline viral rhinotracheitis (FVR), and many other upper respiratory viruses not yet completely characterized but similar to FVR.