The present status of anthelmintic resistance in gastrointestinal nematode infections of sheep in the northwest of Spain by in vivo and in vitro techniques.

The aim of this study was to update the anthelmintic resistance (AR) status in sheep flocks infected by gastrointestinal nematodes (GIN) by means of in vivo and in vitro methods in the northwest of Spain. With this objective, we studied the efficacy of benzimidazoles (BZs), imidazothiazoles (IMs) and macrocyclic lactones (MLs), between 2006 and 2011. The sampling area was the Autonomous Community of Castilla y León but the majority of the flocks were located in the province of León. When the mean of GIN eggs per gram (epg) in faeces in a flock was higher than 150, the in vivo Faecal Egg Count Reduction Test (FECRT) was carried out. According to this test, AR was present in 63.6% of flocks, independently of the anthelmintic used. Flocks were mainly resistant to levamisole (LEV) (59.0%), followed by ivermectin (IVM) (27.3%) and albendazole (13.6%). Multidrug-resistance was also observed in 27.2% of the flocks, one of them being resistant to all anthelmintic families, including long-acting moxidectin. Comparing the evolution of AR in the last decade, between 1999 and 2011, the level of resistance to BZs and MLs was fairly constant throughout the time by means of the FECRT. However, the resistance to LEV increased significantly in only one decade since during the period 1999-2003 the percentage was 38.5%. The AR status was also measured by in vitro techniques in those flocks with an egg output lower than 150 epg. The prevalence of AR to BZs reached the 35.3% by Egg Hatch Assay. However, the level of resistance reported for LEV and IVM was 61.5% and 23.5%, respectively, by using the Larval Feeding Inhibition Assay, percentages very similar to those reported with the FECRT.

Characterization of a multidrug resistant Teladorsagia circumcincta isolate from Spain.

The aim of this work was to know the anthelmintic resistance (AR) status of a Spanish sheep flock infected by gastrointestinal nematodes (GIN) and the possible cross resistance among anthelmintics of the macrocyclic lactones (ML) family. The Faecal Egg Count Reduction Test (FECRT) was carried out to check the efficacy of albendazole (Zodalben®), levamisole (LEV) (Endex®) and an oral formulation of ivermectin (IVM) (Oramec®), at the recommended dose rates. Then, the study was extended to check the cross resistance between drugs of the ML family: injectable IVM (Ivomec®), oral moxidectin (Cydectin®), injectable moxidectin (Biodectin®) and doramectin (Dectomax®), at the recommended dose rates. The GIN species were identified after faecal cultures in all groups. The FECRT showed the resistance of a Teladorsagia circumcincta isolate against LEV (39-58%), IVM (88-92%) and doramectin (85%). This study is the first report to confirm the side resistance between these MLs, which belong to the avermectin chemical group, in a Spanish sheep flock. The in vitro efficacy of LEV and IVM was measured by the Larval Feeding Inhibition Assay (LFIA) using the IC(50) measurement (concentration needed to inhibit the ingestion of 50% L1). The values of the multidrug resistant isolate were 0.25 µg/ml for LEV and 3 ng/ml for IVM. Both results were higher than the values obtained with a susceptible isolate, which could be indicative of AR. However, further research examining the response of a greater range of susceptible and resistant nematodes isolates should be carried out to establish a discrimination threshold.

Efficacy of a moxidectin/triclabendazole oral formulation against mixed infections of Fasciola hepatica and gastrointestinal nematodes in sheep.

We have evaluated the efficacy in sheep of a combination drench formulation at the recommended dose rate of 0.2 mg moxidectin/kg bodyweight and 10 mg triclabendazole/kg bodyweight against an experimental infection with Fasciola hepatica and a natural infection with gastrointestinal nematodes. We confirmed that the efficacy of reducing fecal egg output was 98.3% for trichostrongyle eggs and 100% for F. hepatica eggs. Based on adult worm and fluke recovery, the efficacy varied according to the target species. A reduction was found in the number of Teladorsagia circumcincta, Trichostrongylus spp., Nematodirus spp., and Trichuris spp. greater than 95%, but the efficacy for Oesophagostomum spp. varied, with values below 90%. The reduction in F. hepatica was higher than 95% for all stages. The effectiveness of the formulation was also confirmed by an increase in total proteins and albumin following treatment.

Ecological relations among first-stage larvae of four species of Protostrongylidae (Nematoda) within their ovine host.

Competitive relations between protostrongylid nematodes parasitic in the ovine lung, using competition coefficients and asymptotic densities showed that two relatively scarce species (Neostrongylus linearis and Protostrongylus rufescens) exert strong competitive actions on the two most abundant species (Cystocaulus ocreatus and Muellerius capillaris). P. rufescens could lead to the disappearance of the more abundant species, if other compensatory factors did not exist in their life cycle.

Population variability of Cernuella arigonis (Haas, 1929) (Mollusca: Helicidae) experimentally infected with Muellerius capillaris (Mueller, 1889) (Nematoda: Protostrongylidae).

Data on the level of infection and stage of larval development at the 12th and 40th days post-infection in the host-parasite system Cernuella arigonis (Haas, 1929) (Mollusca: Helicidae)/Muellerius capillaris (Mueller, 1889) (Nematoda: Protostronglylidae) were obtained. The results show the presence in an area of northern Spain of two varieties, geographic races or even sibling species of the host snail.

Teaching veterinary parasitology throughout the world.

In order to understand how the teaching of parasitology in veterinary schools and faculties in the world is carried out, a questionnaire was sent to all centres listed in the W.H.O. World Directory. A total of 91 replies were received. Additional information was obtained from the report of a symposium held in Hannover, Germany in 1978 and from the Education Committee of the American Association of Veterinary Parasitologists in 1981. The academic level, the place of parasitology in the veterinary curriculum, textbooks and practical instruction, evaluation techniques, teaching staff, institute organization and publications are discussed.

Migration and growth of Neostrongylus linearis (Marotel, 1913) Gebauer, 1932 in sheep.

In order to establish the mammalian parasitic cycle of the nematode Neostrongylus linearis 18 lambs were infected with 5000 third-stage larvae obtained from the snail Cernuella (Xeromagna) cespitum arigonis. In the subsequent days, larvae were found in the walls of the caecum and colon, in the liver and the lungs, suggesting that the bloodstream is the main migratory route. The presence of low numbers of migrating larvae in the mesenteric lymph nodes indicates that this route is probably secondary. The first still sexually undifferentiated, fourth-stage larvae were found in the lungs on the 8th day post-infection (p.i.) and the first sexually differentiated fifth-stage larvae, on the 10th day. Also described are the macroscopic changes of the parasitized organs.