Efficacy and pharmacokinetics of levamisole hydrochloride in goats with nematode infections

Knowledge, attitudes and practices of Australian dairy goat farmers towards the control of gastrointestinal parasites

BACKGROUND

Gastrointestinal parasites such as nematodes and coccidia are responsible for significant economic losses in the goat industry globally. An indiscriminate use of antiparasitic drugs, primarily registered for use in sheep and cattle, in goats has resulted in drug-resistant gastrointestinal parasites. Very little is known about the gastrointestinal parasite control practices used by Australian dairy goat farmers that are pivotal for achieving sustainable control of economically important parasites. The study reported here provides insights into gastrointestinal parasite control practices of Australian dairy goat farmers based on responses to an online survey.

METHODS

The questionnaire comprised 58 questions on farm demography, husbandry and grazing management, knowledge of gastrointestinal parasites and their importance in dairy goats, diagnosis of infections, antiparasitic drugs and alternate control options. After a pilot survey (n = 15 respondents), a link to the questionnaire was available to all (n = 456) registered members of the Dairy Goat Society of Australia Ltd from 17 April to 16 June 2023. Multiple correspondence analyses (MCA) were performed to explore the association between selected parasite control practices.

RESULTS

A total of 66 (14%) respondents completed the questionnaire. Of these, 74% (49/66) observed parasite-related illnesses in their goats; two-thirds of them assessed worms burden using faecal egg counts (FECs), with 26% (39/149) deworming their goats based on the results of the FECs. Most respondents (97%; 183/188) perceived that gastrointestinal parasites caused production losses and ranked Haemonchus contortus as the most important parasite. Anitparasitic drugs were used by 94% (62/66) of respondents, with the most frequently used anthelmintics being a commercial combination of four anthelmintics (levamisole, closantel, albendazole and abamectin), benzimidazoles and macrocyclic lactones. Most respondents (77%; 51/66) were unaware of anthelmintic resistance on their property. MCA results delineated two clusters of gastrointestinal parasites management.

CONCLUSIONS

This study provides insights into the demography of Australian dairy goat farms, the husbandry and grazing practices used by dairy goat farmers, their knowledge regarding gastrointestinal parasites and their practices for internal parasite control, thereby paving the way for tackling drug resistance in gastrointestinal parasites in dairy goats.

World Association for the Advancement of Veterinary Parasitology (W.A.A.V.P.) guideline for diagnosing anthelmintic resistance using the faecal egg count reduction test in ruminants, horses and swine

The faecal egg count reduction test (FECRT) remains the method of choice for establishing the efficacy of anthelmintic compounds in the field, including the diagnosis of anthelmintic resistance. We present a guideline for improving the standardization and performance of the FECRT that has four sections. In the first section, we address the major issues relevant to experimental design, choice of faecal egg count (FEC) method, statistical analysis, and interpretation of the FECRT results. In the second section, we make a series of general recommendations that are applicable across all animals addressed in this guideline. In the third section, we provide separate guidance details for cattle, small ruminants (sheep and goats), horses and pigs to address the issues that are specific to the different animal types. Finally, we provide overviews of the specific details required to conduct an FECRT for each of the different host species. To address the issues of statistical power vs. practicality, we also provide two separate options for each animal species; (i) a version designed to detect small changes in efficacy that is intended for use in scientific studies, and (ii) a less resource-intensive version intended for routine use by veterinarians and livestock owners to detect larger changes in efficacy. Compared to the previous FECRT recommendations, four important differences are noted. First, it is now generally recommended to perform the FECRT based on pre- and post-treatment FEC of the same animals (paired study design), rather than on post-treatment FEC of both treated and untreated (control) animals (unpaired study design). Second, instead of requiring a minimum mean FEC (expressed in eggs per gram (EPG)) of the group to be tested, the new requirement is for a minimum total number of eggs to be counted under the microscope (cumulative number of eggs counted before the application of a conversion factor). Third, we provide flexibility in the required size of the treatment group by presenting three separate options that depend on the (expected) number of eggs counted. Finally, these guidelines address all major livestock species, and the thresholds for defining reduced efficacy are adapted and aligned to host species, anthelmintic drug and parasite species. In conclusion, these new guidelines provide improved methodology and standardization of the FECRT for all major livestock species.

In vivo exposure of Albendazole sulphoxide by Haemonchus contortus and correlation between plasma and target tissue or gastrointestinal content dispositions in goats

Sheep and goats are sharing different helminth parasites including Haemonchus contortus. Control of these helminths is based mainly on the use of anthelmintics. However, in goats, the application of anthelmintics is often carried out mainly at dosages determined for sheep without knowing the real effects and metabolism features. One of the several anthelmintic classes used against these parasites is (pro) benzimidazoles which are still widely in use in small ruminants in many countries. The objective of this study was to determine (i) the correlation between plasma and tissue or gastrointestinal content dispositions of ricobendazole (RBZ) in goats and (ii) the in vivo exposure of ricobendazole by H. contortus. Ten goats were experimentally infected with 10,000 larvae of H. contortus. Four weeks of post-infection, the animals received RBZ subcutaneously at 5 mg/kg body weight. Two goats were sacrificed per time at 1, 2, 4, 6 and 12 h after drug administration and, blood, bile, urine, liver, lung, muscle and kidney gastrointestinal tissues/fluids were collected. Adult H. contortus were collected from abomasum, and all samples were analysed by HPLC system. Ricobendazole (RBZ) and its sulphone metabolite were extensively excreted by urine and distributed to all tissues and digestive tract, mainly into the abomasum fluid. RBZ concentration in the lung and ABZSO₂ in the kidney were relatively higher than those of other tissues, respectively. The parent drug and its metabolite were recovered in both male and female H. contortus. This study indicates that in goats the plasma concentration profiles of RBZ are strongly correlated with those achieved in different target tissues or fluids, which in turn, reflect the amount of drug taken up by parasites.

Pharmacokinetics of an immunomodulating dose of levamisole in weaned pigs

Levamisole has been shown to stimulate the immune response in immunocompromised humans and animals. However, its use as an adjuvant in immunocompromised weaned pigs prone to colibacillosis has only been experimentally tested but not yet officially approved. Therefore, the aim of these studies was to study the pharmacokinetics (PK) of an immunomodulating dose of levamisole in weaned pigs. For that purpose, 20 weaned crossbred pigs were divided into two treatment groups. In this parallel-design study, a single dose of levamisole (2.5 mg/kg body weight) was administered by the intramuscular (i.m.) or oral (p.o.) route. Statistically significant differences between the i.m. and p.o. routes in terminal beta rate constant (β), maximum plasma concentration (Cmax), area under the curve (AUC) for plasma concentration-time curve from time zero to infinity (AUC0-inf), area under the plasma concentration-time curve from time 0 to the last quantifiable time point (AUC0-t) were determined. Further research is needed to establish a relationship between the PK and the immunomodulating effect of levamisole in pigs.

Anthelminthic resistance of Haemonchus contortus in small ruminants in Switzerland and Southern Germany

Two goat and two sheep flocks have been found to be suspicious of a clinically evident reduced anthelmintic efficacy, i.e. lacking improvement of gastrointestinal disorders, insufficient weight gain and continuing inappetence after anthelmintic treatments. In order to conduct an appropriate evaluation of the efficacy the following trials were performed: the faecal egg count reduction test on the studied goats of the two herds revealed a reduction of the egg-excretion after the eprinomectin-treatment (1 mg/kg BW, pour-on) of 17.4% and 27.5%, respectively, which clearly confirms the occurrence of anthelmintic resistance against eprinomectin in these two herds. The alternatively administered moxidectin-treatment (1 mg/kg BW, pour-on) of one flock resulted in a 99.1% faecal egg count reduction. In both sheep flocks, 30 randomly selected sheep were divided in three groups and each group was treated with a different anthelmintic, according to the instructions for use. The faecal egg count reductions for the various groups treated orally with benzimidazoles were 70.8% and 55.3% (albendazole), 52.4% (fenbendazole) and 47.3% (oxfendazole). The two moxidectin-treated groups (0.2 mg/kg BW, oral) showed an EpG-reduction of 100% and 44.3%, respectively, thus also demonstrating resistance against macrocyclic lactones. Pre- and post-treatment faecal larval cultures revealed Haemonchus contortus as the predominant resistant species.