Feline rhinotracheitis vaccine and production and use thereof

A vaccine for immunizing susceptible cats by parenteral inoculation against feline viral rhinotracheitis and for increasing the antibody levels of thus-inoculated cats comprising at least about 10.sup.4 tissue culture infectious doses of an attenuated feline viral rhinotracheitis virus per unit dosage, which vaccine is capable of stimulating the production of protective feline viral rhinotracheitis antibodies comparable to those produced by natural infections when parenterally administered to non-immune cats but which does not produce the usual pathological symptoms of feline viral rhinotracheitis, said virus being attenuated by serially propagating virulent feline rhinotracheitis in feline tissue culture, at incubation temperature lower than that at which the virus remains virulent and does not attenuate in repeated serial passages through feline tissue culture, for a sufficient number of repeated serial passages until inoculation therewith of susceptible cats establishes that the virulence of the virus is so attenuated that upon intranasal administration to susceptible cats, the pathological symptoms of the disease are not observed in the inoculated cats, but there is formed therein antibodies against feline viral rhinotracheitis effective to immunize them against infectious viral rhinotracheitis.

A process for the production of an attenuated live feline rhinotracheitis virus from a virulent live feline viral rhinotracheitis virus which will otherwise remain virulent and not attenuate in repeated passages through feline tissue cultures if maintained at 35.degree. C., which comprises propagating said virus for a sufficient number of repeated serial passages through feline tissue cultures maintained at an incubation temperture within the range of from about 28.degree. C. to about 32.degree. C., until intranasal administration to susceptible cats establishes that the virulence of the virus is so attenuated that the pathological symptoms of the disease are no longer observed, with the formation in said vaccinated cats of antibodies against feline viral rhinotracheitis effective to immunize and completely protect said vaccinated cats against feline viral rhinotracheitis as evidenced by subsequent challenge of said vaccinated cats with virulent feline viral rhinotracheitis, and none developing the pathological symptoms of feline viral rhinotracheitis.