Simultaneous resistance to multiple anthelmintic classes in nematode parasites of cattle in New Zealand

Resistance to the benzimidazole and macrocyclic lactone anthelmintics is widespread in Cooperia spp. on cattle farms in New Zealand. Since this was first documented in 2006 little has changed in cattle farming systems except for the widespread use of levamisole to control Cooperia spp. in young cattle (i.e., parasite control has maintained an almost total reliance on use of anthelmintics). Here we report the emergence of simultaneous resistance to the benzimidazole, macrocyclic lactone and levamisole anthelmintics in Cooperia spp. and in Ostertagia spp. Anthelmintic efficacy against nematode parasites of cattle was investigated on four commercial farms following reports of poor animal growth rates and welfare, and positive faecal egg counts, despite routine treatment with combination anthelmintics, which included levamisole. Faecal egg count reduction tests involved 15 animals per treatment group, individual egg counts (paired samples) conducted pre- and post-treatment, with eggs counted to ≤ 15 eggs per g faeces and larval cultures for morphological identification. Actives tested varied between farms but always included levamisole alone and several combination products containing levamisole. Of the 20 tests conducted (i.e., 5 products on each of 4 farms) only 3 exceeded 90% efficacy against Cooperia spp. even though 8 of the products tested were combinations containing levamisole and at least one other broad-spectrum anthelmintic. Levamisole used alone achieved efficacies between 44% and 71% against Cooperia spp. across the four trials. The only product to exceed 95% efficacy against Cooperia spp. was a combination of monepantel + abamectin which was 100% effective against all parasites. Resistance to oxfendazole in Ostertagia spp. was indicated on 3 farms, while on one farm efficacy of all the tested products was ≤75% against this parasite. All the farms involved in this study were farming intensive cattle operations with an almost total reliance on anthelmintics to control parasitism. The results clearly demonstrate the emergence of simultaneous resistance to oxfendazole, levamisole and the macrocyclic lactone anthelmintics. Despite years of advice and recommendations to change farming practices away from intensive monocultures, many farmers have continued with the practice, and some are now faced with the very real possibility of being unable to control cattle parasites on their farms.

Monitoring equine ascarid and cyathostomin parasites: Evaluating health parameters under different treatment regimens

BACKGROUND

Strongylid and ascarid parasites are omnipresent in equine stud farms, and ever-increasing levels of anthelmintic resistance are challenging the industry with finding more sustainable and yet effective parasite control programs.

OBJECTIVES

To evaluate egg count levels, bodyweight and equine health under defined parasite control protocols in foals and mares at two Standardbred and two Thoroughbred stud farms.

STUDY DESIGN

Longitudinal randomised field trial.

METHODS

A total of 93 foals were enrolled and split into two treatment groups, and 99 mares were enrolled and assigned to three treatment groups. All horses underwent a health examination, and episodes of colic or diarrhoea were recorded at each faecal collection date. Bodyweights were assessed using a weight tape, and mares were body condition scored. Group A foals (FA) were dewormed at 2 and 5 months of age with a fenbendazole/ivermectin/praziquantel product, while group B foals (FB) were dewormed on a monthly basis, alternating between the above-mentioned product and an oxfendazole/pyrantel embonate product. Group A mares (MA) were dewormed twice with fenbendazole/ivermectin/praziquantel, group B mares (MB) were dewormed with the same product, when egg counts exceeded 300 strongylid eggs per gram, and group C mares (MC) were dewormed every 2 months, alternating between the two products. Health data were collected monthly for 6 months (foals) and bimonthly for 13 months (mares). Data were analysed with mixed linear models and interpreted at the α = 0.05 significance level.

RESULTS

There were no significant bodyweight differences between foal groups, but MA mares were significantly lighter than the other two groups. Very few health incidents were recorded. Foals in group FA had significantly higher ascarid and strongylid egg counts, whereas no significant differences were observed between mare groups.

MAIN LIMITATIONS

Study duration limited to one season.

CONCLUSIONS

Anthelmintic treatment intensity was lowered from the traditional intensive regimes without measurable negative health consequences for mares and foals.

Abomasal nematode species differ in their in vitro response to exsheathment triggers

A crucial step in the infection process of grazing ruminants by gastro-intestinal nematodes is the exsheathment of the infective third-stage larva following ingestion. Recently, heat shock was shown to play an important role in the carbon dioxide (CO₂)-dependent exsheathment response in Haemonchus contortus. The current in vitro study set out to evaluate the role of heat shock in other abomasal species. In rumen fluid, all species tested exsheathed rapidly and efficiently in response to heat shock and CO_2. This response was significantly higher compared to slow temperature changes, supporting the hypothesis that heat shock plays an important role in vivo. However, in artificial buffer, the effect of heat shock was species-dependent. For H. contortus and Ostertagia leptospicularis, the response in artificial buffer was similar to rumen fluid. In contrast, Ostertagia ostertagi and Teladorsagia circumcincta exsheathment was significantly lower and/or slower in artificial buffer, and there was no benefit of heat shock. For these two species, it appears that there are co-factors in the rumen fluid, in addition to heat shock and CO₂, contributing to exsheathment. Overall, the data indicate that there are significant differences between abomasal species in their response to exsheathment triggers.