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.
