Interaction of a combined feline viral rhinotracheitis-feline calicivirus vaccine and the FVR carrier state

Abstract

The effect of field feline viral rhinotracheitis (FVR) virus challenge on cats previously vaccinated with a combined FVR/feline calicivirus intramuscular vaccine was studied in relation to the development of an FVR carrier state. There was no virus shedding of either of the two vaccine viruses following vaccination. Treatment with corticosteroid 60 days after vaccination and before challenge with FVR virus did not induce virus re-excretion in vaccinates or controls; neither did similar treatment induce shedding 63 days after challenge of both vaccinates and controls with virulent field virus. After a further 55 days however, FVR virus shedding was elicited in one of four previously vaccinated and challenged cats compared with two of four unvaccinated and challenged controls. Two sentinel cats remained virologically and serologically free of FVR throughout. The vaccine was shown to be effective in controlling the disease; 12 weeks after initial vaccination no clinical signs were seen in three of four cats following intranasal challenge with 10(5)CCID50 of virulent field FVR virus, and a mild transient unilateral ocular and nasal discharge was seen in the remaining cat for one day only. Severe clinical signs of approximately 10 days' duration were seen in all four unvaccinated challenged controls. The virological and serological responses of the cats were also recorded.

Isolation of Felid Herpesvirus I from the Trigeminal Ganglia of Latently Infected Cats

“…This may have been a combined effect of the small number of cats in each group and the low overall isolation rate. However, these negative results do reflect in vivo findings described previously, where preliminary work using corticosteroid treatment and oropharyngeal swabbing as an indicator of latent infection also suggested that such cats did not become virus carriers (Orr et al, 1980).…”

Feline Viral Upper Respiratory Disease

“…Again, however, immunity is not necessarily complete in all animals, even if challenge takes place within 3 months of vaccination. 78,84,85 Similar levels of protection have been reported after a year. 86 More recent studies have shown that the relative efficacy of an inactivated vaccine decreased from 83% shortly after primary vaccination to 52% after 7.5 years.…”

Feline herpesvirus

“…All types of vaccine induce reasonable protection against disease in previously unexposed cats. However, none of the vaccines appears to protect against infection or the development of the carrier state, although both viral shedding and latency load of wild-type virus after viral challenge may be reduced in vaccinated cats compared to unvaccinated controls [28,70,99,100,130,147]. Although intranasal vaccine virus can become latent [147], the situation with parenterally vaccinated cats is still unclear [130].…”

“…Although the majority of cats are protected against disease following the use of modified live or inactivated FeHV-1 vaccines, a proportion of cats will still show mild signs, even if challenge takes place within 3 months of the initial vaccination [6,64,99,109,116,155]. However a significant reduction in overall clinical scores can generally be shown in vaccinates compared to controls, although the level of protection does decrease as the vaccination interval increases.…”