Alarming levels of anthelmintic resistance against gastrointestinal nematodes in sheep in the Netherlands.

In a survey involving 34 sheep flocks spread over the Netherlands anthelmintic resistance (AR), based on a fecal egg count reduction (FECR) test, was determined for six different products. The study was conducted in ewes shortly after lambing during spring 2015. A FECR of less than 90%, indicating presence of AR against one or more nematode genera producing strongylid eggs, was found in 22 of 30 (73.3%) flocks against oxfendazole, 18 of 23 (78.3%) flocks against ivermectin, 15 of 32 (46.9%) flocks against moxidectin, and 2 of 26 (7.7%) flocks against monepantel. No AR was observed against levamisole. If oxfendazole resistance was observed, Haemonchus contortus was involved in 90.5% of the cases. If resistance against ivermectin, moxidectin or monepantel was observed, it invariably involved H. contortus. In the majority of cases resistance was also observed for Teladorsagia circumcincta and/or Trichostrongylus spp, between which no distinction was made in this study. Based on FECR 9 of 15 (60.0%) flocks showed resistance against closantel, which was mainly due to closantel not being effective against most other nematode species than H. contortus. However, in 44.4% of flocks showing reduced FECR it did involve H. contortus as well. Multi-drug resistance (excluding closantel) was found in 16 flocks, of which 8 showed resistance against 2 products, 7 against 3 products and 1 flock showed resistance against 4 products. If resistance against 3 or 4 products was present, there invariably was resistance against both ivermectin and moxidectin. Overall, of the 22 flocks in which both macrocyclic lactones (ML) were tested, 4 (18.2%) showed no resistance against both products, 9 (40.9%) showed resistance against ivermectin only, and 9 (40.9%) showed resistance against both MLs. It is concluded that AR is widespread in sheep in the Netherlands and involves products from all major anthelmintic classes, with possibly the exception of levamisole. It appears that the macrocyclic lactones have lost much of their efficacy against sheep nematodes over the last decade.

Ploeger HW ，Everts RR 《-》

Anthelmintic resistance in Northern Ireland (I): prevalence of resistance in ovine gastrointestinal nematodes, as determined through faecal egg count reduction testing.

The prevalence of anthelmintic resistance in Northern Ireland sheep flocks was evaluated between July and October 2011. Sampling kits were sent to 172 flock owners and returns were received from 91. Within this survey population, 27 flock owners used benzimidazole products, 10 used levamisole products, 15 used avermectin products, 26 used milbemycin products and 4 flock owners used the amino acetonitrile derivative, Monepantel. The remaining 9 flock owners used combination drenches (broad spectrum wormer plus fasciolicide). However, 15 sets of samples were ineligible for faecal egg count reduction testing due to either too low an egg count or insufficient faecal volume. Treatment efficacy below 95%, indicating significant resistance, was detected in 81% (n=24) of flocks tested for benzimidazole resistance; in 14% (n=1) of flocks tested for levamisole resistance; and in 50% (n=7) and 62% (n=13) of flocks tested for avermectin and milbemycin resistance, respectively. Monepantel resistance was absent in all (n=3) flocks tested. Combination products (broad spectrum nematocide plus flukicide) containing levamisole were entirely effective, while treatment efficacy below 95% was detected in 60% (n=3) of flocks where the nematocide in the combination product was a benzimidazole. Where parasite identification based on coproculture was completed, Trichostrongylus was the dominant genus detected in all cases post-treatment, indicating the occurrence of anthelmintic-resistant Trichostrongylus spp. populations. Benzimidazole efficacy was highest in treating Trichostrongylus spp. (51%) and lowest when treating Teladorsagia spp. Levamisole was 100% effective in treating Cooperia, but ineffective (0%) in treating Trichostrongylus spp. Avermectin efficacy was highest when treating Haemonchus contortus (100%) and Teladorsagia spp. (73%), with a marginally lower efficacy against Trichostrongylus spp. (71%). Moxidectin efficacy was 33% against Trichostrongylus spp., 68% against Teladorsagia spp., 97% against Cooperia spp. and 100% against Haemonchus contortus infections.

McMahon C ，Bartley DJ ，Edgar HW ，Ellison SE ，Barley JP ，Malone FE ，Hanna RE ，Brennan GP ，Fairweather I ... -  《-》

Efficacy of closantel against ivermectin- and fenbendazole-resistant Haemonchus sp. in sheep in Ontario, Canada.

In Ontario, Canada, widespread resistance to ivermectin and fenbendazole, the only readily available ovine anthelmintics, has been documented, primarily in Haemonchus sp. In other parts of the world, closantel has been used to control such infections; however, the drug was not currently licensed for use in Canada and the USA. A randomized controlled trial was conducted on six client-owned farms in Ontario in 2013 and 2014 to determine the efficacy of closantel (Flukiver® 5% Oral Suspension, Elanco Animal Health, 10mg/kg bodyweight) against ivermectin- and fenbendazole-resistant Haemonchus sp. infections in periparturient ewes and grazing lambs. Three farms were randomly assigned to treat all ewes, and three farms were randomly assigned to selectively treat individual ewes at lambing, using predetermined criteria. Fecal samples were collected from a minimum of 15 randomly selected ewes and 13 lambs per group on each farm at the time of treatment and approximately 14days later. Trichostrongyle-type fecal egg counts (FEC) were performed using a modified McMaster technique with a lower detection limit of 8.3 eggs per gram of feces (epg). Haemonchus-specific FECs were determined by multiplying FECs by the proportion of Haemonchus sp. identified from coproculture for each farm; Haemonchus-specific FEC reductions were calculated for each farm. Twenty grazing lambs had FECs conducted monthly, and when mean monthly FECs surpassed 200 epg, all lambs were randomly allocated to either closantel, positive control (ivermectin, fenbendazole, or levamisole) or negative control groups. Pre-treatment Haemonchus-specific mean FECs ranged from 27 to 3359 epg in ewes and 0-5698 epg in lambs. Efficacy of closantel against Haemonchus sp. ranged from 99% (95% CI: 97%-99%) to 100% in recently lambed ewes on all farms in both years (total n=274 ewes), and from 99% (95% CI: 98%-99%) to 100% in grazing lambs in both years on all but one farm (total n=171 lambs). On the latter farm, a whole flock treated farm, closantel efficacy in grazing lambs was 84% (95%CI: 81%-88%) in the first year, but 100% in the second year. Levamisole was effective against overall GIN in lambs on only two farms. Ivermectin and fenbendazole resistance continued to be present, particularly in Haemonchus sp. Closantel had excellent efficacy against Haemonchus sp. over the two year study period, regardless of treatment group, and therefore should be considered one viable component of sustainable integrated parasite control programs for farms with documented anthelmintic resistance and problems with haemonchosis.

Westers T ，Jones-Bitton A ，Menzies P ，Van Leeuwen J ，Poljak Z ，Peregrine AS ... -  《-》

Anthelmintic resistance in Haemonchus contortus from sheep in Malaysia.

Pandey VS ，Sivaraj S 《VETERINARY PARASITOLOGY》

Revisiting anthelmintic resistance in sheep flocks from São Paulo State, Brazil.

Bassetto CC ，Albuquerque ACA ，Lins JGG ，Marinho-Silva NM ，Chocobar MLE ，Bello HJS ，Mena MO ，Niciura SCM ，Amarante AFT ，Chagas ACS ... -  《International Journal for Parasitology-Drugs and Drug Resistance》