PLANT EXTRACTS USED FOR THE CONTROL OF ENDO AND ECTOPARASITES OF LIVESTOCK: A REVIEW OF THE LAST 13 YEARS OF SCIENCE

A variety of endo and ectoparasites can affect livestock, causing poor animal performance and low welfare conditions. Haemonchus contortus (Trichostrongyloidae), Rhipicephalus microplus (Ixodidae), Cochliomyia sp. and Lucilia sp. (Calliphoridae) are some of the most important parasites to livestock in Brazil and in many other tropical and subtropical countries, where farmers need to be vigilant. Although a constant parasite control uses large-spectrum anthelmintics or synthetic insecticides, giving a timely potent reduction of the infections, they also represent a threat to the lifespan of these compounds due to drug-selected parasites. Thus, the development of plant-based therapies is a solid alternative for standard, agroecological, and holistic farming systems, as well as it is an important ally to combat drug resistant parasite populations. In this article, we discussed the scientific literature on plant extracts, notably hydroalcoholic extract or essential oils, used for the control of the above livestock parasites published in the last 13 years. Our objective was to pinpoint the most important issues for this promising area of research, exploring the potential and the challenges that are facing us by examining more than 150 in vitro and in vivo studies. Almost all the authors reported positive data from plants or isolates, the most important challenges that were faced during our search were the lack of a proper experimental study design, and the deficiency in the characterization of the plants used. It is our opinion that plant-based products may be a solid choice for parasite control in livestock animals achieving high welfare standards and mitigate farming input (i.e. use of chemicals and their waste into the environment).


INTRODUCTION
Livestock production is an important activity worldwide that requires knowledge and the application of modern technologies to be effective and profitable. Welfare conditions of farm animals integrates the health status of livestock and depends on many management strategies that focus in alleviating the imposed stress conditions, i.e. high animal density, contact with infection agents (virus, bacteria, parasites), unbalanced nutrition, and short gestational intervals. In developing countries, particularly those located in tropical and subtropical regions, gastrointestinal nematode infections, acute and chronic), can significantly delay production, decrease revenues and, in extreme cases, life cycle, these molecules play an important role to their adaptation to the environment, generating advantages in competition and perpetuation of some species. For example, they may be involved in the pollination process or in the biological defense, acting as chemical defenders against microorganisms, insects, larger predators or even other plants (Balandrin et al., 1985). Most of secondary metabolites can be classified into three chemically distinct groups: terpenoids, synthesized mainly from mevalonic acid or 6 Plant extracts used for the control of endo and ectoparasites of livestock: a review of the last 13 years of science Archives of Veterinary Science, v.25, n.4, p. 01-27, 2020.
apathy, weight loss, anemia, diarrhea, and even death of young animals. To control these infections, farmers usually use conventional anthelmintic products in preventive programs (Fortes and Molento, 2013). Several alternatives have been suggested to overcome this problem and the use of herbal medicines is in an advanced stage of research, showing promising data (Seddiek et al., 2011;Adenubi et al., 2016;Pavela and Benelli, 2016).
The articles listed in Table 1  However, the toxicity of synthetic insecticides and the negative effects on human health and the environment, coupled with the development of insecticide resistance, led to a recovery of the interest in low-impact botanical insecticides (Pavela, 2015). The great need large scale studies to determine the real effective concentrations, even including populations that are geographically distant. Despite the increase on studies of plant extracts for myiasis control, some gaps remain to be filled. In Table 3, we note that 52.63% of the papers did not describe which part of the plant were used. Similarly, 89.47% of them did not show the chemical composition of the evaluated plant. Therefore, our opinion is that these data are incomplete, representing an important limitation regarding high-quality scientific information to base alternative forms of treatments for ecto and also to endoparasites of livestock. These limitations are particularly important for all reports and we still have to address this issue to be able to better contribute to the phytotherapy field of science.

Challenges and opportunities to the science of phytotherapy
Phytotherapy, as well as herbal medicine/herbalism, and ethnoveterinary, is a regular form of medical science and must be treated so, using all the available technology for its development and distinguished growth. The traditional use of herbs/plants has given rise to a modern discipline, which must comply to scientific standards, not relying in empirical appreciation and old knowledge (Ameh et al., 2010).
The World Health Organization -WHO, has given support to the broad use and regulation of herbal medicine, even to the support of clinical trials and the evaluation of their residues (WHO, 2000(WHO, , 2005(WHO, , 2007. Pharmacological activity of plant-derived isolates (effect, persistency, quality, safety/toxic signs, biosynthesis, drug-drug interaction and combination), must be a priority for novel data determinations, as we want to suggest their use in substitution to commercial products. The combination of herbal medicines and commercial products is An extra perspective is the false impression, from common users, that plant derive products are safer to the environment. Related to this, the risk of host toxic effect is also a major factor to be taken into account, as the skin can be damaged after an overdose of an isolate. Thus, apart from being a real possibility of substitution, some questions have Molento et al. (2020) Archives of Veterinary Science, v.25, n.4, p. 01-27, 2020.   p.195-198, 2011.