Parasites, Plants and Nobel Prizes
The use of plants to eradicate or control parasites is deeply embedded in all cultures. Even monkeys have been observed to self-medicate with herbs when they suffer from intestinal parasites.1 Hence it follows that the use of antiparasitic plants will be of veterinary as well as human relevance. 2 This has been borne out by a recent study on wormwood (Artemisia absinthium) and dog ticks (Rhipicephalus sanguineus). The brown dog tick is found worldwide, but more commonly in warmer climates. Although it feeds on a wide variety of mammals, dogs are the preferred host and it is frequently associated with kennels. As it is one of the most important vectors of diseases in dogs, this tick has importance in the transmission of diseases to humans. The objective of the study was to evaluate the in vitro efficacy of different concentrations of extract from the aerial parts of wormwood in comparison to amitraz on adults, eggs and larvae of the dog tick. This was assessed using the adult immersion test (AIT), egg hatchability test (EHT) and the larval packet test (LPT). Five concentrations of the extract (1.25, 2.5, 5, 10 and 20%) were used in all the bioassays. A control group was established (water + dimethylsulfoxide) together with a positive control group (amitraz). In AIT, the mortality rates were 0.0, 13.3, 16.7, 33.3 and 93.3% for the concentrations of 1.25, 2.5, 5, 10 and 20%, respectively, and the variation with increasing concentration was significant (p = 0.015). Egg production was reduced by 6.6, 6.6, 18.3, 42.5 and 85.1% in the concentrations of 1.25, 2.5, 5, 10 and 20%, respectively, and was again statistically significant (p = 0.027). In EHT, hatching was inhibited, with 5, 10 and 20% displaying 100% ovicidal action, while at the concentrations of 1.25 and 2.5% inhibition rates were 20 and 60%, respectively. In LPT, the extract caused 100% mortality of larvae in the concentrations of 5, 10 and 20% after 24 hours, while for 1.25 and 2.5% mortality rates were 54.3 and 96.7%, respectively.
This study suggests that the topical use of wormwood (possibly as the tincture and perhaps combined with other acaricidal plants) could be an effective strategy for controlling ticks in dogs. A clinical trial would be the next step.
The use of plants for improving animal health is also being applied to control diseases in organic livestock. This topic was recently the subject of a systematic review that found a total of 590 plant species were used for animal treatment in Europe.3 Most of the research was from France, Italy and Turkey. Again the use of wormwood, in this instance to treat parasites in cattle, featured strongly.
A different antiparasitic wormwood species, sweet wormwood or qing hao (Artemisia annua) made world headlines late in 2015 when Tu Youyou deservedly shared the Nobel Prize for medicine for her discovery of the potent and novel anti-malarial compound artemisinin. This has clearly demonstrated to the world the value of ethnomedicine-based discovery and the relatively untapped potential of medicinal plants. It was a landmark event for herbal clinicians and puts paid to the nonsense that “anything worthwhile in medicinal herbs has already been discovered decades ago”.
More than the usual obstacles had to be overcome by the tenacious and dedicated natural product scientist. To quote from a recent article from the Lancet stable:4 “Extraction and characterisation of Artemisia alkaloids took years of rigorous work under the supervision of experienced scientists including Youyou Tu, but the pressure of the Cultural Revolution in the early 1970s forced the investigators to a rather unusual “phase 1 trial” of the phytochemical artemisinin: testing it on themselves as a necessary step to ensure the successful development of Artemisia as antimalarial drug. After surviving the pressure of the Chinese political elite, the death of Mao in 1976, and the dismissal of Project 523, Artemisia still had to face its hardest battle: becoming an accepted therapy outside of China. Cold war tactics permeated the publication of the early clinical experience within the Chinese medical literature, with the western scientific community remaining mostly sceptical to the antimalarial properties of Artemisia. It remained a relatively unattractive form of Chinese whisper until the early 2000s, when, after a careful appraisal of the literature in absence of political pressures, the first artemisininbased combination therapy became part of the WHO pharmacopoeia for the treatment of malaria.”
References 1 Kenemans P. Maturitas 2004; 48(Suppl 1): S1-S3 2 Xi S, Liske E, Wang S et al. Evid Based Complement Alternat Med 2014; 2014: 717686 3 Fritz H, Seely D, McGowan J et al. Integr Cancer Ther 2014; 13(1): 12-29 4 Wu CT, Lai JN, Tsai YT. PLoS One 2014; 9(12): e113887
5 Davis VL, Jayo MJ, Ho A et al. Cancer Res 2008; 68(20): 8377-8883
References 1 Huffman MA. Proc Nutr Soc 2003; 62(2): 371-381 2 Godara R, Parveen S, Katoch R et al. Parasitol Res 2014; 113(2): 747-754 3 Mayer M, Vogl CR, Amorena M et al. Forsch Komplementmed 2014; 21(6): 375-386 4 Pinato DJ, Stebbing J. Lancet Oncol 2015; 16(7): 759-760