Ethnoveterinary plants with antiviral activity against feline herpesvirus type 1

Abstract

Ethnoveterinary studies conducted in South Africa commonly record indications of medicinal plant use for non-specific, general ailments. Few studies suggest that rural livestock-owners are able to successfully diagnose viral diseases in their animals. Plants widely used to treat undefined ailments in ethnoveterinary medicine (EVM) may have antiviral activity. Sixteen plants featuring prominently in EVM were collected and acetone extracts of the leaves prepared. These extracts were tested against feline herpesvirus type 1, an enveloped virus sensitive to environmental effects. Cytotoxicity tests on the host cells, Crandell feline kidney (CRFK), were performed concomitantly with the antiviral assays. Each extract, at a concentration of 1mg/ml redissolved in 0.5% DMSO, was incubated with the virus for a defined contact time of 20 minutes before a serial dilution in cell culture medium was performed. The dilutions were then applied to confluent monolayers of CRFK cells and observed for cytopathic effect (CPE) after incubation. One extract, Croton gratissimus, was highly toxic to the CRFK cells and antiviral effects could not be detected. Six plants (37.5%), including the commonly used medicinal plants Ziziphus mucronata, Rhus lancea and Leonotis leonurus, displayed no effect on the virus, and three extracts (19%, Pouzolzia mixta, Pterocarpus angolensis and Hippobromus pauciflorus) showed a 1 log reduction in viral growth. A 2 log reduction in viral growth was shown by Pittosporum viridiflorum and Cussonia spicata extracts (12.5%). A quarter of the extracts, namely Combretum caffrum, Ricinus communis, Schotia brachypetala and Sclerocarya birrea, resulted in a 3 log reduction in viral effect. The positive results obtained in this screening exercise potentially justify the use of these plants in EVM, and provide impetus for testing the extracts against more resistant viruses encountered in livestock animals such as lumpy skin disease, and this is being pursued.