Abstract:
Viral infections remain a major threat to humans and animals and there is a crucial need for
new antiviral agents especially with the development of resistant viruses. The hexane,
dichloromethane, acetone and methanol extracts of six plant species selected for their
traditional use against infections were tested for in vitro antiviral activity against canine
distemper virus (CDV), canine parainfluenza virus-2 (CPIV-2), feline herpesvirus-1 (FHV-1)
and lumpy skin disease virus (LSDV). All extracts were tested for their cytotoxicity using a
colorimetric tetrazolium-based (MTT) assay and were tested for antiviral efficacy at
concentrations below CC50 values on the various cell types used in this study. The antiviral
activity of extracts was tested using virucidal and attachment assays. In the virucidal assay,
extracts were incubated with virus prior to infection. The most potent inhibition was
observed with the acetone and methanol extracts of Podocarpus henkelii against CDV and
LSDV, which inhibited replication of the viruses by >75% at 3 mg/ml with selectivity index
(SI) values ranging between 12 and 45. Excellent activity was also found with the hexane
extracts of Plumbago zeylanica and Carissa edulis against CDV, with the extracts reducing
viral-induced CPE by 50% and 75% respectively. The hexane extract of C. edulis had moderate
activity against FHV-1 with EC50< 70 mg/ml and SI value <2. Only the acetone extract of P.
henkelii moderately inhibited replication of LSD virus in the attachment assay, with low
activity in other extracts. Of the four extracts with significant antiviral activity, two were
prepared from P. henkelii. Therefore, future work will focus on isolating and characterizing
the substance(s) responsible for bioactivity in extracts of this species
