Efficacy of selected southern African plants used in ethnoveterinary medicine against ticks and associated infections

Abstract

Ticks cause many problems in cattle worldwide, including transmission of tick-borne diseases and quality issues. Attachment of ticks to host organisms causes wounds which enhance the likelihood of secondary infections and abscesses. The aim of this project was to select southern African plants used in ethnoveterinary medicine to repel or kill ticks, to confirm their efficacy against ticks, and to investigate the activity of the plant extracts against bacteria and fungi implicated in causing secondary infections accompanying tick infestations. Eight plants were selected and extracted using acetone, ethanol and sterile distilled water. The extracts were tested against tick larvae using repellence and mortality assays. The minimum inhibitory concentration of each extract against bacterial strains of Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive), as well as the yeast fungal strain Candida albicans, was determined using the broth microdilution assay. Extracts were also tested for their ability to prevent and disrupt bacterial biofilm formation, and for cytotoxicity against bovine dermis and Vero cells. In general, the extracts had better tick repellence than acaricidal effects. Aloe ferox extracts had the highest repellence against tick larvae, as well as the best acaricidal effects at a concentration of 10 mg/ml. Ethanolic extracts of Aloe ferox (MIC = 0.05 mg/ml) and Lavandula lanata (MIC = 1.25 mg/ml) had the best antibacterial activity against E. coli and S. aureus respectively, whereas the acetone extract of Ptaeroxylon obliquum (MIC = 0.02 mg/ml) had the best antifungal activity. For the biofilm inhibitory activity, water extracts of A. ferox (92%), P. obliquum (91%) and Tulbaghia violacea (97%) were able to strongly inhibit biofilm formation after 24 h of treatment. Overall, T. violacea showed promising results with percentage inhibitions close to 100% for all three extracts after 24 h of extract treatment against biofilm formation. After 48 h, only the water extracts continued to inhibit the biofilm effectively. Aloe ferox had SI values as high as 4.88 and 18.75 against Vero cells and BD cells respectively. In summary, water extracts had strong antibiofilm and tick repellence activity, but were not acaricidal, antibacterial or antifungal. Ethanolic extracts had good overall activity in all the assays, and Aloe ferox and Lippia javanica were the most active plant species in the study.