Background: Feline herpesvirus 1 (FHV-1) is a common cause of respiratory and ocular disease in cats. Especially in young kittens that have not yet reached the age of vaccination, but already lost maternal immunity, severe disease may occur. Therefore, there is a need for an effective antiviral treatment. In the present study, the efficacy of six antiviral drugs, i.e. acyclovir, ganciclovir, cidofovir, foscarnet, adefovir and 9-(2-phosphonylmethoxyethyl)-2, 6-diaminopurine (PMEDAP), against FHV-1 was compared in Crandell-Rees feline kidney (CRFK) cells using reduction in plaque number and plaque size as parameters.
Results: The capacity to reduce the number of plaques was most pronounced for ganciclovir, PMEDAP and cidofovir. IC50 (NUMBER) values were 3.2 microg/ml (12.5 microM), 4.8 microg/ml (14.3 microM) and 6 microg/ml (21.5 microM), respectively. Adefovir and foscarnet were intermediately efficient with an IC50 (NUMBER) of 20 microg/ml (73.2 microM) and 27 microg/ml (140.6 microM), respectively. Acyclovir was least efficient (IC50 (NUMBER) of 56 microg/ml or 248.7 microM). All antiviral drugs were able to significantly reduce plaque size when compared with the untreated control. As observed for the reduction in plaque number, ganciclovir, PMEDAP and cidofovir were most potent in reducing plaque size. IC50 (SIZE) values were 0.4 microg/ml (1.7 microM), 0.9 microg/ml (2.7 microM) and 0.2 microg/ml (0.7 microM), respectively. Adefovir and foscarnet were intermediately potent, with an IC50 (SIZE) of 4 microg/ml (14.6 microM) and 7 microg/ml (36.4 microM), respectively. Acyclovir was least potent (IC50 (SIZE) of 15 microg/ml or 66.6 microM). The results demonstrate that the IC50 (SIZE) values were notably lower than the IC50 (NUMBER) values. The most remarkable effect was observed for cidofovir and ganciclovir. None of the products were toxic for CRFK cells at antiviral concentrations.
Conclusion: In conclusion, measuring reduction in plaque number and plaque size are two valuable and complementary means of assessing the efficacy of an antiviral drug. By using these parameters for six selected antiviral drugs, we found that ganciclovir, PMEDAP, and cidofovir are the most potent inhibitors of FHV-1 replication in CRFK cells. Therefore, they may be valuable candidates for the treatment of FHV-1 infection in cats.