Introduction
Melaleuca alternifolia, commonly known as the tea tree (Holliday, Reference HOLLIDAY2004), is a species of tree or tall shrub from the myrtle family (Myrtaceae). Endemic to Australia, it occurs at the southeast Queensland, the north coast and an adjacent range of New South Wales. It grows along streams and in swampy areas, and is often the dominant species in these ecosystems. The tea tree is a small plant, up to 7 m high, with a bushy crown and a whitish, papery bark. The leaves are arranged alternately, sometimes scattered or whorled. The leaves are smooth, soft, linear in shape, 10-35 mm long and 1 mm wide. They have prominent glands, and are therefore rich in oil. Flowers occur in white or cream-colored masses of spikes, 3-5 cm long over a short period, mostly from spring to early summer. The small woody, cup shaped fruit, 2-3 mm in diameter, are scattered along the branches (Holliday, Reference HOLLIDAY2004).
The natural substances from tea tree are commonly used in the pharmaceuticals production and agriculture. In the recent years, the interest for biologically active plant substances has been increased in the European countries, Japan and USA (Puvača et al., Reference PUVAČA, ČABARKAPA, BURSIĆ, PETROVIĆ and AĆIMOVIĆ2018). The specific characteristics of the myrtle family are useful for distilling essential oils. Tea tree has been used as an alternative medicinal plant for almost a century in Australia, as a primary species for essential oil commercial productions (Carson et al., Reference CARSON, HAMMER and RILEY2006). The tea tree essential oil is commonly used as a topical antiseptic and antibacterial because of its distinguishing antimicrobial features. It reduces inflammation and may be effective in fungal infection treatments (Hammer et al., Reference HAMMER, CARSON, RILEY and NIELSEN2006).
Essential or volatile oils are aromatic liquids, extracted by distillation from plant parts, such as flowers, buds, seeds, leaves, twigs, bark, wood, fruits and roots. Because of their valuable properties and active substances, they may have a role in broiler chicken production (Popović et al., Reference POPOVIĆ, PUVAČA, KOSTADINOVIĆ, DŽINIĆ, BOŠNJAK, VASILJEVIĆ and ĐURAGIĆ2016). The aromatic oils used in broiler chickens and laying hens diets include oils from oregano (Origanum vulgare), mugwort (Artemisia vulgaris), tea tree (Melaleuca alternifolia), turmeric (Curcuma longa), peppermint (Mentha piperita), rosemary (Rosmarinus officinalis), sage (Salvia officinalis), cinnamon (Cinnamomum zeylanicum), thyme (Thymus vulgaris), ginger (Zingiber officinale), eucalyptus (Eucalyptus sp.) and garlic (Allium sativum). The most common plants used for essential oils production are cedar (Juniperus virginiana), lavender (Lavandula angustifolia), chamomile (Matricaria chamomilla), lemon myrtle (Backhousia citriodora) and orange (Citrus sinensis). These are used as nutritive additives to feed and drinking water, but also in maintaining facility sanitation (Puvača et al., Reference PUVAČA, STANAĆEV, GLAMOČIĆ, LEVIĆ, PERIĆ, STANAĆEV and MILIĆ2013).
The tea tree essential oil should not be ingested in large amounts due to its toxicity, although no lethal cases have been reported in the medical literature, which was confirmed by Hammer et al. (Reference HAMMER, CARSON, RILEY and NIELSEN2006). The addition of appropriate concentrations of tea tree essential oil in broiler chicken diets have increased average daily gain by 7% and improved feed utilisation by 6%, when compared to the control group (Khattak et al., Reference KHATTAK, RONCHI, CASTELLI and SPARKS2014). The same experiment demonstrated that an increase in tea tree essential oil concentration in chicken diets did not change the average daily gain, however feed utilisation and nutrient digestibility were amplified by 7% and 8%, respectively, while average feed consumption was decreased by 2% (Khattak et al., Reference KHATTAK, RONCHI, CASTELLI and SPARKS2014).
Escherichia coli and Aspergillus fumigatus are two pathogens which are frequently present in poultry flocks, causing severe diseases (Ebani et al., Reference EBANI, NAJAR, BERTELLONI, PISTELLI, MANCIANTI and NARDONI2018). Poor hygiene conditions and animal immunodeficiency increase the severity of the infection (Popović et al., Reference POPOVIĆ, PUVAČA, KOSTADINOVIĆ, DŽINIĆ, BOŠNJAK, VASILJEVIĆ and ĐURAGIĆ2016). Currently, antibiotics are used in resolving bacterial infections, but their application has certain disadvantages. According to Ebani et al. (Reference EBANI, NAJAR, BERTELLONI, PISTELLI, MANCIANTI and NARDONI2018), the most undesirable consequences are the occurrence of antibiotic residues in meat and eggs and the selection of multi-drug resistant pathogens, which could be spread within the farm populations, as well as among other animals. The use of compounds derived from plants, such as essential oils, may be a good alternative to antibiotics, especially in hatcheries and for caged layers (Puvača, Reference PUVAČA2018). Furthermore, poultry meat and eggs, are highly susceptible to Salmonella spp. infections (Cui et al., Reference CUI, BAI, LI, LIU and LIN2018). Salmonella typhimurium and S. enteritidis are recognised as the most frequent pathogens in food-borne sporadic infection outbreaks. In order to decrease the potential risks and preserve meat and its products, natural antimicrobial agents, such as the tea tree essential oil, can be employed as an additive to the poultry nutrition, according to Cui et al. (Reference CUI, BAI, LI, LIU and LIN2018). Alongside antibacterial treatments in poultry production, the control of insects, ticks and mites is important. The control of mealworm (Alphitobius diaperinus) and poultry red mite (Dermanyssus gallinae) are recognised as one of the most important challenges for the poultry production (Tomasi et al., Reference TOMASI, ZORTÉA, RODRIGUES DOS REIS, QUINTANA SOARES LOPES, DALLAMEABALDISSERA, CHRIST VIANNA SANTOS, BARETTA, MOURA STEFAN and SCHAFER DA SILVA2018; Puvača et al., Reference PUVAČA, PETROVIĆ, NIKOLOVA, POPOVIĆ, ČABARKAPA, BURSIĆ, POPOVIĆ, ĐURAGIĆ and SHTYLLA-KIKA2018a).
Bearing in mind the deficiency of available literature data, the aim of this review paper was to collect and summarise available information on the antimicrobial, antioxidant and acaricidal properties and effects of tea tree (Melaleuca alternifolia) and its essential oils in poultry production.
Tea tree essential oil antimicrobial properties
Tea tree extract has a long history of use as a topical antiseptic (Markham, Reference MARKHAM1999), and, in recent years, it has gained a reputation of a safe, natural and effective antiseptic. The chemical composition of the tea tree essential oil has been well defined, and consists largely of cyclic monoterpenes (Brophy et al., Reference BROPHY, DAVIES, SOUTHWELL, STIFF and WILLIAMS1989), where half of them are oxygenated and other half are hydrocarbons. Tea tree essential oil exhibits broad spectrum antimicrobial activity, which principally could be attributed to its terpinen-4-ol content (Southwell et al., Reference SOUTHWELL, HAYES, MARKHAM and LEACH1993; Carson and Riley, Reference CARSON and RILEY1995). A wide variety of essential oils are known to possess antimicrobial properties, where in many cases, this activity is conditioned by the presence of the active monoterpene constituents. Several studies have revealed that monoterpenes exert membrane damaging effects. The electron microscopy of E. coli cells after exposure to tea tree essential oil revealed a loss of the cellular electron dense material and coagulation of cytoplasmic constituents, although, it was apparent that these effects were secondary consequences that occurred after cell death (Gustafson et al., Reference GUSTAFSON, LIEW, CHEW, MARKHAM, BELL, WYLLIE and WARMINGTON1998). Tea tree essential oil stimulates leakage of cellular potassium ions and inhibits respiration in E. coli cell suspensions, providing evidence of a lethal action related to cytoplasmic membrane damage (Cox et al., Reference COX, GUSTAFSON, MANN, MARKHAM, LIEW, HARTLAND, BELL, WARMINGTON and WYLLIE1998). Cox et al. (Reference COX, MANN, MARKHAM, BELL, GUSTAFSON, WARMINGTON and WYLLIE2000) reported antimicrobial activity for the tea tree essential oil against three clinically significant microorganisms: E. coli, S. aureus and C. albicans. According to this study, tea tree essential oil inhibited respiration in E. coli, S. aureus and C. albicans cells at various minimum inhibitory levels (MIC). The possibility that tea tree essential oil directly inhibited a specific respiratory enzyme or metabolic event cannot be excluded, according to these authors, however these findings revealed that exposure to this essential oil altered cell membrane structure. Increased uptake of the propidium iodide nucleic acid stain, to which the cell membrane is normally impermeable, was observed. Moreover, the leakage of potassium ions commenced immediately upon adding the tea tree essential oil to the suspensions containing E. coli, and within 5 min for S. aureus cells.
Ebani et al. (Reference EBANI, NAJAR, BERTELLONI, PISTELLI, MANCIANTI and NARDONI2018) have tested sixteen different essential oils against E. coli and A. fumigatus isolated from poultry, and concluded that tea tree essential oil had no effects on E. coli, although significant effects were confirmed for A. fumigatus (MIC of 1.780 mg/ml). The same authors stated that the efficacy of tea tree essential oil must be thoroughly studied, bearing in mind that experiment was conducted on two phylogenetically distant organisms, but both of which are involved in impairing poultry health and hygiene.
Ding et al. (Reference DING, YU, SU and ZHANG2017) investigated the effects of commercial products containing tea tree essential oil on performance, egg quality, nutrient digestibility and yolk fatty acid profile in Lohmann laying hens, aged 53 weeks, using diets supplemented with 0, 50, 100 and 150 mg/kg of the essential oils. The hen-day egg production and feed conversion ratio showed considerable improvements, while eggshell thickness was significantly increased. However, albumen height, Haugh unit and egg yolk colour were not affected by the tea tree essential oil addition in the diets. Ding et al. (Reference DING, YU, SU and ZHANG2017) reported that addition of tea tree essential oil had a significant influence on protein digestibility. Moreover, saturated and monounsaturated fatty acid gradually decreased, while polyunsaturated fatty acid increased, but this was not significant. This study suggested that the supplementation of the tea tree essential oils in laying hen diets did not show a significant positive effect on performance and yolk fatty acid composition, but tended to increase eggshell thickness and protein digestibility.
Nimbarte and Kulkarni (Reference NIMBARTE and KULKARNI2013) investigated volatile oils of tea tree for antibacterial activity against different avian pathogens isolated from infected chickens: E. coli, S. aureus, S. epidermidis, S. carnosus and S. gallinarum. Antimicrobial activity was assessed by using disc diffusion, MIC and MBC methods. The tea tree volatile oil exhibited activity against all the pathogens. Mean inhibition zones, MIC and minimum bactericidal concentration (MBC) values for the bacterial strains varied from 19 and 34 mm, 0.03%-0.15% to 0.07-0.3%, respectively. Gas chromatography-mass spectrometry (GC-MS) analysis of the tea tree essential oil highlighted the presence of 16 components. Major compounds were limonene, γ-terpinene, α-terpinene, cineol and α-terpinolene. Since aromatic and medicinal plants produce a wide variety of volatile terpenes, hydrocarbons and their corresponding oxygenated isoprenoid derivatives and analogues, the bactericidal effect observed in the Nimbarte and Kulkarni (Reference NIMBARTE and KULKARNI2013) study may be attributed to these components. Hence, tea tree essential oil could be a useful source of new therapeutic and antimicrobial agents suitable for the use in poultry production.
Hammer et al. (Reference HAMMER, CARSON and RILEY2011) examined the effect of subinhibitory tea tree essential oil on the development of antibiotic resistance in S. aureus and E. coli. The frequencies of the single-step antibiotic-resistant mutants were determined by inoculating bacteria, cultured with or without subinhibitory tea tree essential oil onto agar, containing two to eight times the MIC of each antibiotic and with or without tea tree essential oil. Although the differences in resistance frequencies were relatively minor, the combination of kanamycin and the tea tree essential oil yielded approximately 10-fold fewer resistant E. coli mutants than kanamycin alone. The development of multistep antibiotic resistance was examined by culturing S. aureus and E. coli isolates for six days with antibiotics, antibiotics plus tea tree essential oil and antibiotics plus terpinen-4-ol. Median MICs for each antibiotic were increased four to 16-fold by the sixth day. Subinhibitory tea tree essential oil or terpinen-4-ol did not greatly alter results, as the sixth day median MICs was either the same or one concentration different from those obtained for antibiotics alone. For tea tree essential oil and terpinen-4-ol alone, the sixth day median MICs increased from the baseline values, four-fold for S. aureus and two-fold for E. coli. Lastly, Hammer et al. (Reference HAMMER, CARSON and RILEY2011) noticed few significant changes in antimicrobial susceptibility for S. aureus and S. epidermidis isolates that had been serially subcultured 14 to 22 times with subinhibitory terpinen-4-ol, so these data indicated that tea tree essential oil and terpinen-4-ol have little impact on the development of antimicrobial resistance and susceptibility.
Aćimović et al. (2017 and 2018) showed high antimicrobial activity of Angelica archangelica as well as essential oil of wild Angelica seeds. Kabir Mumu and Mahboob Hossain (Reference KABIR MUMU and MAHBOOB HOSSAIN2018) determined tea tree essential oil abilities to control pathogen bacteria: S. aureus, S. pyogenes, P. aeruginosa, P. vulgaris, A. hydrophila, E. coli, S. pneumoniae, B. subtilis, K. pneumonia and S. agalactiae, which are important in poultry production. After 24 h incubation, tea tree essential oil demonstrated a minimum of 96.94% against E. coli and maximum of 100% inhibition against seven other bacteria. The tea tree essential oil had a certain degree of antimicrobial properties, with the highest activity index (1.6) against S. agalactiae. Furthermore, tea tree essential oil exhibited an observable zone against all the bacteria contrariwise, among nine antibiotics only two of them showed a noticeable zone of inhibition to all the bacteria tested.
Candidiasis is a mycotic disease of the digestive tract of the various avian species, including chickens, turkeys and quail caused by C. albicans. It is commonly developed after application of various antibiotics or when unsanitary drinking facilities are used. Lesions are most frequently found in the crop and consist of thickened mucosa and whitish, raised pseudomembranes. The in vitro activity of a range of essential oils, including tea tree, was examined against the yeast candida in Hammer et al. (Reference HAMMER, CARSON and RILEY1998) study. Of the 24 essential oils tested by the agar dilution method against C. albicans ATCC 10231, three did not inhibit C. albicans at the highest concentration (2.0% (v/v) oil). The tea tree essential oil was tested against 81 C. albicans isolates and 33 non-albicans Candida isolates. Using the broth microdilution method, the minimum concentration of oil inhibiting 90% of isolates for both C. albicans and non-albicans Candida species was 0.25% (v/v). The minimum essential oil concentration, lethal for 90% of isolates, was 0.25% for C. albicans and 0.5% for non-albicans Candida species. Using the agar dilution method, Hammer et al. (Reference HAMMER, CARSON and RILEY1998) tested the sensitivity of 57 Candida isolates to tea tree essential oil, where the minimum essential oil concentration inhibiting 90% of isolates was 0.5%. These data indicated that some essential oils were active against Candida spp., suggesting that they may be useful in dietary treatment of candida infections.
According to Kabir Mumu and Mahboob Hossain (Reference KABIR MUMU and MAHBOOB HOSSAIN2018), the tea tree essential oil demonstrated remarkable antibacterial activity. Consequently, it can be expected that tea tree extracts will gradually take place of conventional antibiotics for bacterial infection treatment in poultry production.
Tea tree essential oil antioxidant properties
The research on the bioactive principles of essential oils extracted from different herbs and spices has been increasing, due to their many functional properties, such as antimicrobial, antioxidant, and anticancer activities (Leal et al., Reference LEAL, BRAGA, SATO, CARVALHO, MARQUES and MEIRELES2003; Gulluce et al., Reference GULLUCE, SOKMEN, DAFERERA, AAR, OZKAN, KARTAL, POLISSIOU, SOKMEN and SAHIN2003; Puvača et al., Reference PUVAČA, KOSTADINOVIĆ, POPOVIĆ, LEVIĆ, LJUBOJEVIĆ, TUFARELLI, JOVANOVIĆ, TASIĆ, IKONIĆ and LUKAČ2016). As a result, essential oils have been widely used in fumigants, cosmetics, and aromatherapeutic agents. Nowadays, research is focusing on the pharmacological properties of essential oils, obtained from aromatic and medicinal plants, for usage in poultry feed and as a natural alternative to synthetic drugs (Puvača et al., Reference PUVAČA, STANAĆEV, GLAMOČIĆ, LEVIĆ, PERIĆ, STANAĆEV and MILIĆ2013; Puvača et al., Reference PUVAČA, LJUBOJEVIĆ, KOSTADINOVIĆ, LUKAČ, LEVIĆ, POPOVIĆ and ĐURAGIĆ2015; Kostadinović et al., Reference KOSTADINOVIĆ, PUVAČA, POPOVIĆ and LEVIĆ2015; Popović et al., Reference POPOVIĆ, PUVAČA, KOSTADINOVIĆ, DŽINIĆ, BOŠNJAK, VASILJEVIĆ and ĐURAGIĆ2016). Among them, the tea tree essential oil is one of the most important studied subjects, because of its wide spectrum of activities.
The tea tree essential oil is mainly extracted by steam distillation from Melaleuca alternifolia, which, however, bears no resemblance to the taste or odour of the real tea, Camellia sinensis, Camelliaceae. Malenčić et al. (2018) reported the dietary phenolics and antioxidant capacity of several legume seeds from the Central Balkans. The tea tree essential oil contains approximately 100 compounds, mainly monoterpenes, sesquiterpenes, and their alcohol derivatives, among which terpinen-4-ol, γ-terpinene, α-terpinene, α-terpineol, α-terpinolene and 1,8-cineole are the major components. International standards require that commercial tea tree essential oil has a minimum terpinen-4-ol content of 30%, and a maximum 1,8-cineole content of 15%. However, most customers want to buy tea tree essential oil products containing the highest content of terpinen-4-ol and the lowest content of 1,8-cineole. It has been found that terpinen-4-ol has strong antimicrobial (Cox et al., Reference COX, MANN and MARKHAM2001) and anti-inflammatory effects (Hart et al., Reference HART, BRAND, CARSON, RILEY, PRAGER and FINLAY-JONES2000), while 1,8-cineole, known as eucalyptol, is probably an allergen that is undesirable in essential oil products (Carson and Riley, Reference CARSON and RILEY2001). Although the various properties of tea tree essential oil have been investigated in recent years, such as antibacterial, antifungal and anti-inflammatory (Brand et al., Reference BRAND, GRIMBALDESTON, GAMBLE, DREW, FINLAY JONES and HART2002), its antioxidant activity and bioactive components have not been reported. Therefore, it is necessary to further explore the relationship between terpenic compounds and antioxidant activity in tea tree essential oil in order to provide a more complete characterisation of its bio-functional benefits. Moreover, additional knowledge of the antioxidant activity of the tea tree essential oil may help to increase its market value and usage as phytobiotic in the poultry production.
Many studies have shown that natural antioxidants in aromatic and medicinal plants are closely related with their bio-functionalities. They are considered responsible for the reduction of chronic diseases such as DNA damage, mutagenesis, carcinogenesis (Zhu et al., Reference ZHU, HACKMAN, ENSUNSA, HOLT and KEEN2002) and inhibition of pathogen bacteria growth of (Giroux et al., Reference GIROUX, OUATTARA, YEFSAH, SMORAGIEWICZ, SAUCIER and LACROIX2001), which are often associated with the termination of the free radical propagation in biological systems. Thus, antioxidant capacity is widely used as a parameter to characterise medicinal plants and their bioactive components.
Kim et al. (Reference KIM, CHEN, WU, WANG, CHUNG and JIN2004) investigated the antioxidant activity of the tea tree essential oil, using two complimentary in vitro assays: the 2,2-diphenyl-1-picrylhydrazyl free radical scavenging assay and the hexanal/hexanoic acid assay. In addition, some tea tree essential oil components showed strong antioxidant activity, when separated from the crude tea tree oil by silica gel open column chromatography and C18-high-pressure liquid chromatography and identified by gas chromatography-mass spectrometry. The antioxidant activities of the tea tree essential oil and its bioactive components were compared with a commercial standard antioxidant, butylatedhydroxytoluene. The antioxidant activities of five blended oils from limonene, lavender, pepper mint, eucalyptus, and tea tree oil were measured by the inhibition of 1, 1- diphenyl 2-picrylhyorazyl (DPPH), nitric oxide (NO), and reactive oxygen species (ROS) (Park et al., Reference PARK, LIM, PARK, HUH and HWANG2017). All the oils demonstrated about 90% DPPH inhibitory scavenging ability. Blending oils showed a decrease of 20% and 30% NO inhibitory scavenging ability at concentrations of 0.001 and 0.01‰, respectively. Three blended oils did not show a significant decrease of LPS-induced ROS generation. Tea tree and eucalyptus oil had higher activities on DPPH and NO comparing to the other oils. The tea tree oil showed the strongest ROS activity among the all tested oil products, according to Park et al. (Reference PARK, LIM, PARK, HUH and HWANG2017). The antioxidant activities of the samples seem to be based on their free radical scavenging capacity. The inhibitory activity was higher when the complex (blended) substance was used, rather than the single substance itself.
Essential oils are complex mixtures isolated from the aromatic plants which may possess antioxidant and anti-inflammatory activities of interest in the food and feed and could be a useful tool for improving poultry meat (Džinić et al., Reference DŽINIĆ, PUVAČA, TASIĆ, IKONIĆ and OKANOVIĆ2015) and in laying hen diets (Spasevski et al., Reference SPASEVSKI, PUVAČA, PEZO, TASIĆ, VUKMIROVIĆ, BANJAC, ČOLOVIĆ, RAKITA, KOKIĆ and DŽINIĆ2018). A review by Graca Miguel (Reference GRACA MIGUEL2010) on the antioxidant and anti-inflammatory activities of several aromatic plants and essential oils, as well as a survey on the methods generally used for the evaluation of antioxidant activity and some of the mechanisms involved in the anti-inflammatory activities have been published.
Idris et al. (Reference IDRIS, ABBAS, MASOOD, REHMAN, FAROOQ, BABAR, HUSSAIN, RAZA and RIAZ2017) stated that the poultry industry is currently facing a serious problem in controlling coccidiosis, due to the drug resistance development against commonly available anticoccidials, which is in agreement with the research of Kostadinović et al. (Reference KOSTADINOVIĆ, PUVAČA, POPOVIĆ and LEVIĆ2015) in broiler chickens. Furthermore, an increasing demand from consumers for drug residue free poultry and poultry products, has led to the development of the alternative strategies for the treatment and control of avian coccidiosis as well. In response to the invasion of Eimeria species in coccidiosis, oxidative stress is created by the host cellular response, which imparts pathology to the host tissue besides damaging the parasite. To alleviate the damage caused by oxidative stress during coccidiosis, the use of essential oils rich in antioxidant compounds is being considered as an appealing approach according to Idris et al. (Reference IDRIS, ABBAS, MASOOD, REHMAN, FAROOQ, BABAR, HUSSAIN, RAZA and RIAZ2017). However, results vary and are often not as satisfactory as expected.
Essential oils have the potential to serve as an alternative to anticoccidials (Kostadinović et al., Reference KOSTADINOVIĆ, PUVAČA, POPOVIĆ and LEVIĆ2015). The in vitro antioxidant activity of the tea tree essential oil was evaluated in research by Zhang et al. (Reference ZHANG, GUO, GUO, JIANG and JI2018). The antioxidant potential was evaluated by DPPH, thiobarbituric acid reactive species (TBARS) assay and the hydroxyl radical scavenging activity methods. Tea tree essential oil was able to reduce DPPH with an EC50 (concentration for 50% of maximal effect) of 48.35 μg/ml, inhibit the lipid peroxidation with an IC50 (50% inhibitory concentration) of 135.9 μg/ml, and eliminate hydroxyl radicals with an EC50 of 43.71 μg/ml, which indicated that the tea tree essential oil could serve as a very powerful natural based tool in oxidative stress reduction in poultry production.
Tea tree essential oil acaricidal properties
Among ticks, Ixodes ricinus is one of the most efficient vectors of pathogens such as Borrelia burgdorferi s.l., Ehrlichia (Anaplasma phagocytophilum) and Rickettsia helvetica, which are responsible for the transmission of many diseases. Although the hosts of preference for adult ticks are medium sized or large ungulates, their multi host behaviour gives them considerable opportunities to spread pathogens among numerous animal species, including poultry, and to transmit infections that can be extremely serious. One way of combating this effectively is to reduce contact between humans and vector arthropods, not only by limiting visits, whether for work or recreational purposes, to habitats at risk, such as the forests, but by endeavouring to control the tick population (Jurišić et al., Reference JURIŠIĆ, PETROVIĆ, RAJKOVIĆ and NIĆIN2010). The most widely used methods for tick populations control are based on the application of synthetic acaricides, both in the environment and to animals. However, the inadequate use of these substances inevitably leads to the resistance and a negative impact on the environment. There is a need to reduce the use of synthetic acaricides and to introduce alternative and supplementary methods for tick population control (Jurišić et al., Reference JURIŠIĆ, PETROVIĆ, RAJKOVIĆ and NIĆIN2010). Previously published results indicate promising effects have been achieved using entomopathogenic bacteria and extracts of the certain plants.
The essential oils of Azadirachta indica (neem tree) and of Ocimum suave have shown acaricidal and repellent properties on Amblyomma variegatum larvae and all stages of Hyalomma anatolicum excavatum and Rhipicephalus appendiculatus (Mwangi et al., Reference MWANGI, HASSANALI, ESSUMAN, NYADAT, MOREKA and KIMONDO1995; Ndumu et al., Reference NDUMU, GEORGE and CHOUDHURY1999; Kaaya, Reference KAAYA2000; Abdel-Shafy and Zayed, Reference ABDEL-SHAFY and ZAYED2002). According to current knowledge, the properties of tea tree essential oil have not been tested for tick control. These oils are known to possess bacteriostatic and germicidal properties and are used to as treatments for infections of the skin and mucous membranes. Their apparent insecticidal and acaricidal properties have, to date, been tested on some ectoparasites, such as the head lice and Sarcoptes scabiei (Walton et al., Reference WALTON, MYERSCOUGH and CURRIE2000; McCage et al., Reference MCCAGE, WARD, PALING, FISHER, FLYNN and MCLAUGHLIN2002). On the basis of previous findings Iori et al. (Reference IORI, GRAZIOLI, GENTILE, MARANO and SALVATORE2005) designed a study to test the efficacy of tea tree essential oil against nymphs of I. ricinus at different doses (4, 6, 8 and 10 ml) and for varying exposure times (30, 60, 90 and 120 min). A dose of 8 ml of tea tree essential oil was lethal for more than 70% of ticks when inhaled, and this effect was enhanced when the dose was increased to 10 ml (>80%). The effect was correlated with the duration of ticks’ exposure to the tea tree essential oil, with a significant effect observed after 90 min.
The repellent effects of the tea tree essential oil emulsions and two β-cyclodextrin complex formulations, a slow release form and a modified faster release form, were examined in a series of experiments conducted by Yim et al. (Reference YIM, BHANDARI, JACKSON and JAMES2016). In this research, emulsions containing 4% and 5% of tea tree essential oil was applied to cattle hair in laboratory studies, completely repelled ascending tick larvae for 24 h, whereas 2% and 3% formulations provided 80% protection. At 48 h, 5% the tea tree essential oil provided 78% repellence but lower concentrations repelled less than 60% of larvae. In a study conducted over 15 days, 3% tea tree essential oil emulsion applied to cattle hair provided nearly 100% repellence for two days, but then protection fell to 23% by the fifteenth day. The faster formulation gave significantly greater repellence than the emulsion and the slow realise formulation from the third day until the end of the study, providing almost complete repellence at the third day (99.5%), then decreasing over the period of the study to 49% repellence at the fifteenth day.
Lam et al. (Reference LAM, LONG, GRIFFIN, CHEN and DOERY2018) summarised possible effects of lowering mite counts, relieving symptoms and modulating the immune system, especially inflammatory response, using tea tree essential oil and its extract terpinen-4-ol, as an effective tool in moderating demodex-related diseases. This research showed typical treatments of the tea tree essential oil and extract terpinen-4-ol in human demodicosis, their possible mechanisms of actions, side effects and potential resistance in treating this condition. Although current treatments, other than the tea tree essential oil and extract terpinen-4-ol, are relatively effective for the demodex mite population control and the related symptoms, more research on the efficacy and drug delivery technology is needed in order to assess its potential as an alternative treatment with minimal side effect profile, low toxicity and low risk of demodex resistance.
Using contact bioassays, Fang et al. (Reference FANG, CANDY, MELLOUL, BERNIGAUD, CHAI, DARMON, DURAND, BOTTEREL, CHOSIDOW, IZRI, HUANG and GUILLOT2016) concluded that 1% clove and palmarosa oil killed all the mites within 20 and 50 min, respectively. The efficacies of prospected oils are shown as follows: clove, palmarosa, geranium, tea tree, lavender, manuka, bitter orange and eucalyptus, followed by Japanese cedar. In fumigation bioassays, the efficacy order was: tea tree, clove, eucalyptus, lavender, palmarosa, geranium, Japanese cedar, bitter orange and manuka. Fang et al. (Reference FANG, CANDY, MELLOUL, BERNIGAUD, CHAI, DARMON, DURAND, BOTTEREL, CHOSIDOW, IZRI, HUANG and GUILLOT2016) concluded that essential oils, especially tea tree, clove, palmarosa and eucalyptus oils, are potential complementary or alternative products to treat S. scabiei infections in poultry, as well as to control these mites in the environment.
The toxicity of a range of plant essential oils to the poultry red mite, Dermanyssus gallinae, a serious ectoparasitic pest of laying hens worldwide, was assessed in research of George et al. (Reference GEORGE, SPARAGANO, PORT, OKELLO, SHIEL and GUY2010). It is known that D. gallinae may cause losses in egg production, anaemia and, in extreme cases, death of hens. With changes in legislation and consumer demand, alternatives to synthetic acaricides are needed to manage this pest. The results of George et al. (Reference GEORGE, SPARAGANO, PORT, OKELLO, SHIEL and GUY2010) suggested that the tea tree essential oil may make an effective botanical pesticide for use against D. gallinae. However, it is likely that issues relating to the consistency of the toxic effect of some oils will determine which will be most effective in practice, which is in accordance with the findings of Puvača et al. (Reference PUVAČA, ČABARKAPA, BURSIĆ, PETROVIĆ and AĆIMOVIĆ2018). A positive acaricidal effect of essential oils was shown in research by Pritchard et al. (Reference PRITCHARD, KÜSTER, GEORGE, SPARAGANO and TOMLEY2016), regarding impeding movement of the poultry red mite between hosts. The findings of Iori et al. (Reference IORI, GRAZIOLI, GENTILE, MARANO and SALVATORE2005) showed that tea tree essential oil has acaricidal properties and could be extremely useful in controlling insects, ticks and mites.
Conclusions
Based on the literature, it can be concluded that tea tree (Melaleuca alternifolia) and its essential oil could be used as a powerful antimicrobial, antioxidant and acaricidal natural tool as an effective alternative to synthetic chemicals currently used against Gram-positive and Gram-negative bacteria and different species of insects, ticks and mite, which cause large economical loses in poultry production. Futhermore, tea tree extract is a powerful natural antioxidant and could be used in the poultry nutrition for stress reduction during the production cycle and when exposed to various pathogens. Further investigations of tea tree essential oil and its modes of action in the poultry nutrition are more than necessary to standardise active compound levels and effective inclusion rates in feed.
Acknowledgements
This paper is a part of the project III 46012 which is financed by Ministry for Education, science and technological development of the Republic of Serbia.
