Killers in our midst (Leptospires): Potential Fijian Herbal Remedies for Leptospirosis

Vasiti Uluiviti

Research output: ThesisDoctoral Thesis

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Leptospirosis is caused by the bacterium Leptospira interrogans. Even though leptospirosis is a treatable disease, fatal human cases continue to be reported in Fiji where the following Leptospira interrogans serovars have been implicated in outbreaks: L. interrogans serovar Australis, L. interrogans serovar Bulgarica, L. interrogans serovar Canicola, L. interrogans serovar Copenhageni, L. interrogans serovar Cynopteri and L. interrogans serovar Hardjo. Most victims are farmers and rural dwellers who acquire the infection after a heavy rainfall or flooding.
The use of plants as remedies for common ailments such as flu-like illness, headaches and coughs are a common practice in Fiji. In the Pacific region, there is little documentation on ethnobotanical practices. This research aimed to first survey the literature on these practices in the Pacific Islands, to establish perception versus reality in both the general use of traditional herbal medicines and specifically their use to treat the symptoms of leptospirosis. Secondly, the potential anti-leptospiral properties of leaves of selected Fijian plants were screened for bioactive antimicrobial compounds. Plant selection was based on previous reports of antimicrobial properties, easy accessibility in Fiji; and commonly used as herbal remedies in Fiji. Ten promising plants with their species and local Fijian names include: Cananga odorata Hook. F. & Thomson (Mokosoi); Carica papaya L. (Weleti); Citrus limon (L.) Burm. f. (Moli karokaro); Colocasia esculenta (L.) Schott (Dalo); Euodia hortensis J. R. Forst. & G. Forst. (Uci); Ipomoea batatas (L.) Lam. (Kumala); Merremia peltata (L.) Merr. (Wadamu); Mikania micrantha Kunth (Wabosucu); Polyscias fruticosa (Danidani); and Plumeria rubra L. (Bua).
Ethnobotanical surveys from this study indicated that Pacific Islanders continue to use plants as herbal remedies for common ailments, including some symptoms of leptospirosis, with a variety of preparation and application methods.
The in vitro minimum inhibition concentration (MIC) of the ethanol, acetone and water extracts of the ten selected plants showed varying degrees of antileptospiral activity against four L. interrogans serovars (serovar Australis was non-viable). The average MIC (MIC average) values observed for the ethanol and acetone extracts for the four viable serovars ranged from 0.02 to >10.0 mg/mL; and for the water extracts from 2.50 to >10.0 mg/mL. Three plants showed high potency against L. interrogans serovar Canicola with the lowest observed MICaverage values of 0.02 mg/mL for Euodia hortensis (Uci) and Mikania micrantha (Wabosucu) and 0.16 mg/mL for Merremia peltata (Wadamu).
GC-MS analysis of the various phytochemicals present in the plant extracts were performed. Several compounds were identified as promising antimicrobial compounds that may play a role in the most potent antileptospiral activities of the extracts. The three (3) most abundant of those identified are stigmasterol in M. micrantha, sitosterol in M. peltata, and obtusifoliol in E. hortensis.
Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • Charles Sturt University
  • Kerr, Philip, Principal Supervisor
  • Harper, John, Co-Supervisor
Award date24 Jun 2022
Place of PublicationAustralia
Publication statusPublished - 26 Oct 2022


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