The aqueous extracts of three medicinal plants, Carissa edulis
(Forssk.) Vahl (Apocynaceae), Prunus africana
(Hook.f.) Kalkm (Rosaceae) and Melia azedarach
L. (Meliaceae) have shown significant reduction in the replication of human cytomegalovirus (HCMV) in human embryonic lung (HEL) fibroblasts cells in vitro. Using the plaque inhibition assay for the determination of anti-viral activity, the HEL fibroblast cells cultured in 24 well plates were infected with 1 x 102
PFU 91S HCMV and treated with various concentrations of the extracts. The plaques formed were counted after 7 days incubation at 37°C in 5% CO2
and the percent plaques inhibited were calculated against infected untreated control. The effective concentrations inhibiting plaque formation by 50% (EC50
) was found between 40 to 80 μg/ml for all the extracts. The cell cytotoxic concentrations (CC50
) for each of the three extracts, by the trypan blue exclusion test, gave a safe therapeutic index. These results have demonstrated the potential anti-viral activities of the extracts of the three medicinal plants at non-cytotoxic concentrations.