Efficacy of a combined oral formulation of derquantel-abamectin against the adult and larval stages of nematodes in sheep, including anthelmintic-resistant strains.

Derquantel (DQL), a semi-synthetic member of a novel anthelmintic class, the spiroindoles, in combination with abamectin (ABA) [as the combination product STARTECT(®)] is a new entry for the treatment and control of parasites in sheep. The 19 studies reported herein were conducted in Australia, New Zealand, South Africa and the United Kingdom to demonstrate the efficacy of derquantel-abamectin (DQL-ABA) against a broad spectrum of gastrointestinal and respiratory nematodes of sheep, and to support registration of the combination product. Eleven studies were conducted using natural or experimental parasite infections with unknown or unconfirmed resistance, while eight studies utilised isolates/strains with confirmed or well characterised resistance to one or more currently available anthelmintics, including macrocyclic lactones. All studies included DQL-ABA and negative control groups, and in selected studies one or more reference anthelmintic groups were included. In all studies the commercial formulation of DQL-ABA was administered orally at 2mg/kg DQL and 0.2mg/kg ABA; placebo was administered in the same volume as DQL-ABA; and reference anthelmintics were administered as per label recommendations, except in one instance where levamisole was administered at twice the label dose. Infection, necropsy, worm collection and worm counting procedures were performed using standard techniques. Efficacy was calculated based on the percentage reduction in geometric mean worm count relative to negative control for each nematode species and lifecycle stage targeted. Twenty-two isolates/strains used in the eight studies targeting resistant worms had proven resistance: three to one anthelmintic class, eleven to two classes and eight to three or more classes; of these resistant strains, 16 demonstrated resistance to a macrocyclic lactone anthelmintic. Regardless of resistance status in the 19 studies, DQL-ABA controlled a broad range of economically important gastrointestinal and respiratory nematode parasites of sheep, as follows: ≥ 98.9% efficacy against Haemonchus contortus (adult and L4); Teladorsagia circumcincta (adult, L4 and hypobiotic L4); Teladorsagia trifurcata (L4); Trichostrongylus axei (adult and L4); Trichostrongylus colubriformis (adult and L4); Trichostrongylus falculatus (adult); Trichostrongylus rugatus (adult); Trichostrongylus vitrinus (adult and L4); Cooperia curticei (adult and L4); Cooperia oncophora (adult and L4); Nematodirus spathiger (adult); Nematodirus battus (adult); Nematodirus spp. (hypobiotic L4); Strongyloides papillosus (adult); Strongyloides spp. (L4); Chabertia ovina (adult); Oesophagostomum venulosum (adult); Dictyocaulus filaria (adult); and Protostrongylus rufescens (adult); ≥ 97.0% efficacy against Trichuris ovis (adult); and ≥ 95.9% efficacy against T. trifurcata (adult). Derquantel-abamectin is a highly effective combination anthelmintic, which will provide an important new tool for controlling helminths of sheep when used in conjunction with sustainable drenching practices.

A questionnaire survey on helminth control on horse farms in Brandenburg, Germany and the assessment of risks caused by different kinds of management.

Control strategies for horse helminths are controversially discussed, and no ideal strategy exists. Presently, the spreading of anthelmintic resistance against all three classes of anthelmintics is of special concern. Advice on how to slow the development of anthelmintic resistance does not seem to have reached the majority of horse owners yet. In our study, we wanted to capture the current standard of helminth control and to analyse the effectiveness of these control strategies. Seven hundred horse farms in Brandenburg, Germany were sent a questionnaire in June/July 2006 asking various questions on farm structure and practices of helminth control. Two hundred thirty-five farms (33.6%) with 6,007 horses in total returned the questionnaire. The number of horses held on each farm varied from 1 to 320. From those returned questionnaires, a random sample of 126 horse farms and 1,407 horses was selected for faecal examination from August to December 2006. The questionnaire results from these farms were correlated with results from the faecal examination to perform risk analysis via multivariate regression. For each farm, results from faecal examination were summarized in index values. Risk was defined as an over-average level of strongyle egg shedding. Risk factors as established by multivariate regression analyses were integrated into three models. Rare deworming and infrequent cleaning of stables were identified as significant risk factors throughout all three models. Additional risk factors could be identified with respect to individual models: elevated percentage of young horses on a farm, not using macrocyclic lactones in the deworming process and dosing anthelmintics on the basis of weight and height. Pasture hygiene did not lead to significant risk reduction, indicating that such measures are inadequately performed on many farms. The questionnaire on its own gave us an insight into control strategies throughout a representative scope of farms in Brandenburg, Germany: faeces were collected from pasture on 22% of horse farms, 79% cleaned out the stables daily. A number of other measures were employed. With respect to anthelmintic use, 21% of the farms stated to use results from faecal examination as a criterion for deworming. We could also identify the most common deworming frequencies, with adult horses being dewormed two times a year (46% of farms) and foals being dewormed four times a year (35% of farms). The frequency ranged from 1 to 7 and 2 to 12 times, respectively.

Prevalence of helminths in horses in the state of Brandenburg, Germany.

The objective of the study was to estimate the prevalence of helminths in the horse population of the state of Brandenburg, Germany. One hundred and twenty-six horse farms in the state were selected by randomised stratified sampling. In total, 1,407 horses across all farms were examined coproscopically. The experimental unit was the horse farm: a farm was considered infected when at least one horse on the farm investigated was positive for helminth eggs. Animal details such as age, breed and sex were collected for all study horses and analysed for risk of infection. Risk was defined as horses having an above-average shedding of strongyle eggs. The following prevalence on horse farm level were established: Cyathostominae (98.4%), ascarids (16.7%), tapeworms (14.3%), pinworms (8.7%) and strongyloides (4,0%). The large strongyle Strongylus vulgaris was identified on only one farm. Liver flukes and lungworms were not found. Age, breed and sex were identified as risk factors for high shedding of strongyle eggs of individual animals: odds ratios for higher shedding intensities were 4.18 for yearlings and 2.42 for fillies compared to adult animals, and 3.69 for heavy breeds and 4.94 for wild horses compared to thoroughbreds. Mares and stallions did shed more strongyle eggs than geldings. Knowledge about the helminth prevalence will allow the issuance of specific treatment recommendations. Furthermore, the information on risk factors of individual horses will facilitate targeting single animals for selective treatments.

Standardization of the egg hatch test for the detection of benzimidazole resistance in parasitic nematodes.

The ability to reliably detect anthelmintic resistance is a crucial part of resistance management. If data between countries are to be compared, the same test should give the same results in each laboratory. As the egg hatch test for benzimidazole resistance is used for both research and surveys, the ability of different laboratories to obtain similar results was studied through testing of known isolates of cyathostomins, Haemonchus contortus, Ostertagia ostertagi, and Cooperia oncophora in programs supported by the EU (Cost B16 and FP6-PARASOL). Initial results showed difficulties in obtaining reproducible and similar data within and between laboratories. A series of ring tests, i.e., simultaneous and coordinated rounds of testing of nematode isolates in different laboratories was subsequently performed. By adopting identical protocols, especially the use of deionized water and making dilutions of thiabendazole in dimethyl sulfoxide in the final ring test, laboratories correctly identified both susceptible and resistant isolates. The protocols for the test and preparation of solutions of thiabendazole are described.