Equine herpesvirus 1 (EHV-1) is an important equine pathogen that causes respiratory disease, abortion,
neonatal death and
paralysis. Although
vaccines are available, they are not fully protective and outbreaks of disease may occur in vaccinated herds. Therefore, there is an urgent need for effective
antiviral treatment. For three abortigenic (94P247, 97P70 and 99P96) and three neuropathogenic isolates (97P82, 99P136 and 03P37), the effect of
acyclovir,
ganciclovir,
cidofovir,
adefovir,
9-(2-phosphonylmethoxyethyl)-2,6-diaminopurine (
PMEDAP) and
foscarnet on plaque number was studied. Additionally, for isolate 97P70, the effect on plaque size was investigated.
Ganciclovir was most potent in reducing plaque number, followed by
PMEDAP and
acyclovir.
Adefovir and
cidofovir were less effective and
foscarnet was the least effective compound. There were no differences detected for
acyclovir,
ganciclovir,
adefovir and
PMEDAP between the abortigenic and neuropathogenic isolates. One abortigenic isolate (99P96) was more susceptible to
cidofovir and two neuropathogenic isolates (99P136 and 03P37) were less susceptible to
foscarnet. For isolate 97P70, all compounds resulted in a significant reduction of plaque size. The most remarkable effect was observed for
cidofovir. It was 40-fold more effective in reducing plaque size than in reducing plaque number. In conclusion,
ganciclovir was the most potent compound and therefore, may be a valuable candidate for the treatment of EHV-1
infections in horses. The
antiviral effect of
foscarnet on plaque number was highly dependent on the viral isolate tested. Therefore, it is no valuable
antiviral for the treatment of
herpesvirus-infections.
Cidofovir, although less effective in reducing plaque number, had a strong effect on plaque size.