Essential oil pharmaceuticals for killing ectoparasites on dogs

Pet companions especially dogs are important family members, but external parasites, particularly ticks and fleas, are among the most common problems affecting dogs. They can cause allergic skin problems, septicaemia, and even death [1]. Furthermore, ticks and fleas are vectors of zoonotic diseases that can be transmitted to humans, such as Query fever, Rocky Mountain spotted fever, Ehrlichosis, and Lyme disease [2]. There are several ticks genera that can be found in pets such as genera Amblyomma, Dermacentor, Ixodes and Rhipicephalus [3]. Furthermore, there are several flea species that can be found in pets such as Ctenocephalides felis, Ctenocephalides canis, Archaeopsylla erinacei, Pulex irritans, Ceratophyllus gallinae [4]. However, tick species Rhipicephalus sanguineus tick species and the Ctenocephalides felis flea species (cat flea) are the most common pests affecting dogs and cats [4, 5, 6]. The entire life cycle of ticks (Rhipicephalus sanguineus) occurs on dog hosts [7] and be completed in 70-126 days under normal environmental conditions and host availability [8], whereas the life cycle of fleas mostly occurs outside dogs [9]. The female fleas can produce 40-50 eggs per day and average of 1,350 eggs over a 50 day period [9]. Flea eggs are laid on the host and then drop from host and can spread into the environment. The entire flea life cycle takes 20–30 days [10]. Chemical pesticides, administered topically, orally, by injection, or through bathing/soaking, are usually used to eliminate ticks and fleas [11]. However, the misuse or excessive administration of these pesticides can poison dogs, and the toxins they contain may remain in the environment.

Herb extracts are alternative treatments for preventing and eradicating many external parasites in animals. For example, the citronella species Cymbopogon nardus (L.) Rendle proved effective for controlling bovine ticks [12]. Additionally, a study conducted by [13] found that Cymbopogon nardus (L.) Rendle was effective against Amblyomma cajennense and Anocentor niten larvae. Study of [14] found that the most abundant constituents of citronella were citronellal, citronellol, and geraniol. Likewise, Mentha piperita (peppermint) effectively controlled internal parasites in rabbits and chickens in British Columbia, Canada [15]. The chemically characterised peppermint was rich in pulegone, menthol, carvone 1, 8-cineole, limonene, and β-caryophyllene [16]. In addition, the Zanthoxylum genus, including Z. caribaeum Lamarck, at a concentration of 5% effectively eliminated the cattle ticks species Rhipicephalus microplus [17]. The active ingredient of the essential oil of the clove species Syzygium aromaticum (eugenol) proved to be effective against Rhipicephalus microplus larvae and adult ticks [18]. In addition, the essential oil of the basil species Hyptis suaveolens was effective against Ixodes ricinus larvae [19].

The Zanthoxylum limonella, citronella, clove, peppermint, and ginger essential oils, which are extracted from locally grown herbs, may provide an alternative means of eliminating external parasites on dogs and be safe for animals, people, and the environment. The objective of this study was to investigate the in vitro efficacy of these five essential oils against dog ticks and fleas and to test the sensitivity of dogs’ skin.

There were no statistically significant differences in the ability of the Z. limonella, citronella, clove, and peppermint essential oils to inhibit the spawning of female engorged ticks at concentrations of 16% (p > 0.05). Studies of [23, 24] revealed that Zanthoxylum armatum from Nepal effectively killed insects, which is relevant to this study. Another study [25] showed a repellent effect of 3% clove oil against Dermacentor reticulatus, with 83% effectiveness. Interestingly, no studies have shown that clove oil can kill ticks. However, citronella oil at 16% concentration was highly tick repellent and reduced the reproductive efficiency of ticks. At concentrations of 16%, the Z. limonella, clove, peppermint, and ginger essential oils were more effective in inhibiting egg laying than the same oils at 2% concentrations, suggesting that higher concentrations of essential oils may have a stronger inhibitory effect on tick egg laying than lower concentrations. This supports the general principle that the concentration of an active ingredient in a substance can influence its efficacy as a repellent or insecticidal agent. In addition, the high standard deviations for the lower concentrations of essential oils (2%, 4%, and 8%) were more widely distributed and varied than those for the higher 16% concentration. This suggests that the higher standard deviations indicated relatively unstable effects at the lower concentrations. In contrast, the smaller standard deviation for the 16% concentration indicated that the effects on egg laying inhibition were more consistent, and the more stable and reliable response to the higher concentration of essential oil had a stronger ability to prevent or reduce the reproductive capabilities of female engorged ticks.

The mortality rate of tick larvae was as high as 99.58% when exposed to 2% citronella oil, whereas [26] observed a mortality rate of 66%. Interestingly, all five essential oils tested in this study were highly effective in treating tick larvae when used at concentrations of 2% or higher. The 50%, 90%, and 99% lethal concentrations (LC₅₀, LC₉₀, and LC₉₉) for the essential oils on tick larvae in 24 h were found to be low values. This represented that all essential oils were highly toxic to tick larva. This suggests that these essential oils have potential as tick control agents during the larval stage and can potentially disrupt the tick life cycle.

The testing of five essential oils against fleas indicated that a concentration of 4% was the most effective in terms of flea control. Specifically, clove oil at a 4% concentration demonstrated the highest efficacy, achieving 100% flea control. However, although the 0.5% concentration of essential oils was effective in killing but it required a longer exposure to achieve the same level of flea control as the 1%, 2%, and 4% concentrations, respectively. In this study, clove oil at the minimal concentration achieved relatively low LC₉₀, and LC₉₉ values, indicating its potency in killing fleas within a short exposure time and highly toxic to fleas. Clove oil was effective in eliminating Ctenocephalides spp. fleas, similar to a study by [26]. However, no study of the effectiveness of the Z. limonella, citronella, peppermint, and ginger essential oils against Ctenocephalides spp. fleas has been conducted.

Essential oils have insecticidal effects by acting on the insects’ nervous systems to inhibit the activity of the acetylcholinesterase enzyme. This leads to an accumulation of acetylcholine, disrupting the normal functioning of the nervous system and affecting the movement and coordination of insects, ultimately leading to their death [27, 28, 29, 30]. Additionally, essential oils may disrupt various metabolic processes in insects, including nutrient absorption, utilisation, and storage. By reducing the availability of essential energy sources, such as protein, fat, and glycogen, insects can be deprived of energy, thus affecting larval growth and development and the reproductive capabilities of adult insects [28, 31].

Clove oil at a concentration of 16% could potentially be developed as a pharmaceutical agent to effectively kill fleas and ticks based on the observation of few side effects 15 min after applying the oil to dogs’ skin. This is important for ensuring the safety and welfare of treated dogs. This study confirmed the effectiveness of essential oils for practical use as tick and flea repellents and eliminators. However, [32] retrospective study from 2006 to 2008 showed that plant-derived flea products containing mixtures of essential oils such as peppermint oil (0.25%–3%), thyme oil (1.7%–5%), 2-phenethypropionate (1.7%–5%), cinnamon oil (1.5%–4.5%), lemongrass oil (1.5%–4.5%), clove oil (1.7%–5%), and isopropyl myristate had potentially adverse effects on dogs. The reported abnormalities, such as lethargy and vomiting, highlighted the need for caution when using essential oils on dogs, which should only be done under veterinary supervision.

This study’s findings will help to understand the problem of killing ticks and fleas on dogs. All essential oil tested as pharmaceutical agent can replace chemical pesticides and be highly beneficial for both consumers and the environment, as well as for increasing the value of local herbal products.