Treatment of visna virus infection in lambs with the acyclic nucleoside phosphonate analogue 9-(2-phosphonylmethoxyethyl)adenine (PMEA).
Fifteen lambs were inoculated intracerebrally with visna maedi virus strain KV1772. Seven lambs were injected s.c. with 10 mg/kg PMEA 3 times a week starting 4 weeks after inoculation with visna maedi virus, when brain infection had been established; the other 8 lambs were controls. After 3 weeks of treatment there was a reduction in the amount of virus isolated from blood cells of PMEA-treated lambs compared with controls and during the remaining 7 months of drug treatment there was significantly less virus isolated from the blood cells of treated lambs than of controls. Antibody response against visna maedi virus was slower in the treated than in the untreated control group. There was no difference in the amount of virus isolated from various organs of the 2 groups and the severity of central nervous system lesions in sheep treated with PMEA for 8 months was comparable to that found in untreated controls, even though PMEA reached concentrations in the cerebrospinal fluid which were well in excess of the EC50 value of the drug for visna maedi virus.