Evaluation of a marketed polyherbal dewormer against intestinal strongyles in naturally infected donkeys

Donkeys play a key role as working animals in developing countries, and they are also used for meat and milk productions, social activities, tourism and leisure (Camillo et al., 2018). Consequently, the interest in the welfare and diseases of this species is constantly increasing (Bonelli et al., 2016; Sgorbini et al., 2017, 2018), including parasitic diseases and strategies for their control.

The high occurrence of large and small strongyles in donkeys has been widely reported (Matthee et al., 2000; Getachew et al., 2010; Matthews et al., 2013; Ismail et al., 2016; Jajere et al., 2016; Dibaba et al., 2017). Intestinal strongyles may negatively affect body conditions, live weight and haematological parameters of donkeys (Matthee et al., 2002; Yoseph et al., 2005) and their control is typically performed by the administration of anti-helminthic drugs licensed for use in horses (Matthee et al., 2002). However, the development of drug-resistant populations of small strongyles have been reported in donkeys (Matthee et al., 2002; Lawson et al., 2015). This factor and the growing consumer trend to ask for food products free of chemical residues, including milk from donkeys raised according to organic farming methods (Camillo et al., 2018), prompt researchers, practising veterinarians, and organic donkey farmers to search for sustainable alternatives to control gastrointestinal parasites in this host species. Among the sustainable alternatives, there are various medicinal plants that are reported to have anthelmintic properties in donkeys (Scantlebury et al., 2013). However, to the best of the authors’ knowledge, the effectiveness of herbal formulations marketed for parasite control in donkeys under field conditions has not been yet investigated so far. Hence, the aim of the present study was to determine the effectiveness of a commercially available polyherbal dewormer, marketed for use in equines, to reduce the faecal output of strongyle eggs in donkeys.

For this study, formal consent is not required. The research related to animals complied with all the relevant national regulations and institutional policies for the care and use of animals.

On day 0, EPG counts ranged from 180 to 700 and from 100 to 770 in faeces of treated and untreated donkeys, respectively. No side effects were observed after treatment. FECR test showed that the polyherbal dewormer produced a very negligible reduction (5 %) of strongyle eggs on day 0 onwards and no reduction or lower reduction (2 %) on day 21 till the end of the study, even though donkeys were treated again with a much higher dose, as adjunct treatment, on day 21. The values of AM±SEM of the EPG counts on day 0 to day 42 in treated and untreated donkeys are presented in Table 1. Unexpectedly, the AMs of the EPG counts were higher in the treated group both on day 14 and on day 21, reaching highly significant differences (P=0.0033 and P=0.0029, respectively). The values of the AMs in the treated donkeys became lower in comparison with their untreated counterpart on day 35 and on day 42 but differences did not reach statistically significant values (P=0.6530 and P=0.1796, respectively).

Results of the FECR test in the present study were compared to cut-off limits proposed by Kaplan and Nielsen (2010) as general guidelines to assess the occurrence of anthelmintic resistance after treatment with drugs currently used in horses, when a recommended range of at least 5 – 10 horses on each farm is included. Reductions >90 % for benzimidazoles and pyrantel or >95 % for ivermectin and moxidectin suggest that the strongyle population is susceptible to the drug tested. Lack of effectiveness is suspected when reductions <80 % for benzimidazoles and pyrantel or <90 % for macrocyclic lactones are found. In this study, only a very negligible reduction (5 %) was seen on day 14. In general, the anthelmintic activity of plants has been reported to be lower than that found for synthetic anthelmintic drugs (Macedo et al., 2010). In addition, Iqbal et al. (2004) reported that an increase in EPG reduction was noted with an increase in the dose of Artemisia brevifolia administered as crude powder, crude aqueous extract, and crude methanol extract against mixed infection of gastrointestinal nematodes in sheep. Similarly, Zajac and Gipson (2000) reported that a single treatment with fenbendazole was able to reduce EPG counts by only 50 % but 2 doses administered in a 12 h interval increased efficacy to 92 % in a goat herd. Thus, it is possible that the dose rate (8 gr of paste/100 kg bodyweight) recommended by the manufacturer for the polyherbal dewormer tested in our study may not be high enough to produce anthelmintic effects in donkeys. For this reason, a second treatment with a much higher dose of the product (50 gr of paste irrespective of the bodyweight) was additionally administered as adjunct treatment on day 21. Despite of this, no egg reduction could be demonstrated on day 35. Moreover, no important differences in individual FECR tests were observed among donkeys treated with the herbal dewormer. Finally, the occurrence of anthelmintic resistance can be excluded since the phytotherapeutic product tested had never been used before in the donkey population of the study. Therefore, our results show that the polyherbal dewormer administered in the present study failed to produce any suitable anthelmintic efficacy against intestinal strongyle infections in donkeys after both the first and mostly the second administration.

Our findings are in agreement with those of other authors. Luginbuhl et al. (2006) reported the lack of anthelminthic effects of a commercially available herbal dewormer to reduce EPG counts in meat goats. Burke et al. (2009a) showed that another marketed herbal dewormer, involving the use of two different formulations, was ineffective to control gastrointestinal nematodes in dairy goats. The two herbal mixtures contained Artemisia absinthium, Allium sativum, Foeniculum vulgare, Juglans nigra, and Stevia rebaudiana as well as Cucurbita pepo, Hyssopus officinalis, and Thymus vulgaris. Similarly, a commercially available certified organic garlic product, fresh garlic juice, and garlic bulbs or papaya seeds failed to control gastrointestinal strongyles in goats and lambs (Burke et al., 2009b). In a field trial to assess the usefulness of a mineral lick containing herbal extracts with anti-parasitic properties for the control of gastrointestinal helminths in grazing sheep, there were no significant differences in the prevalence and intensity of helminth infections between the treated and control groups (Nosal et al., 2016). The commercially available product consisted of the extracts of A. absinthium, Artemisia cina, Tanacetum vulgare, T. vulgaris, A. sativum, Alsidium helminthochorton, Dryopteris filix-mas, Daucus carota, Chenopodium, and Punica granatum. However, contrary to the aforementioned studies, other in vivo investigations have reported the efficacy of some medicinal plants against gastrointestinal strongyles. Iqbal et al. (2004), Masamha et al. (2010), Jabbar et al. (2007), and Tariq et al. (2009) reported the anthelmintic activity of A. brevifolia, A. sativum, Chenopodium album and Caesalpinia crista, or A. absintium in sheep, respectively.

To conclude, the phytotherapeutic potential and pattern of anthelmintic effectiveness of plant extracts vary widely from study to study. Consequently, though phytotherapy has become more and more popular with both donkey breeders and veterinarians, phytotherapic compounds marketed as herbal anthelmintics need evidence-based validation. For this reason, our trial tested the effectiveness of an herbal dewormer against intestinal strongyles in naturally infected donkeys. Based on the FECR test and current criteria used to evaluate the efficacy of anthelmintic drugs, the marketed polyherbal product tested in this study cannot be recommended as an effective alternative or complementary treatment for the control of intestinal strongylosis in donkeys. The findings of our study can help make practitioners aware of the possible disadvantages of natural herbal medicines for the treatment of parasitoses. In our opinion, monitoring FECR test results after treatment with herbal medicines is strongly recommended to provide the equine practitioner with the information necessary to administer extracts of anthelmintic plants consciously. Further in vivo trials focusing on suitable plants with promising potential anthelmintic properties are advisable for the development and the release of commercially available alternative and complementary anthelmintics to be used in donkeys.