Conference Agenda

Anthelmintic resistance is a major problem in the control of parasitic infections in the agriculture industry in many parts of the world. Therefore, understanding the mechanism of drug resistance and the development of new drugs is at the forefront of scientific interest.

Increased anthelmintics inactivation via biotransformation belongs to a significant drug-resistance mechanism. Long-term exposure to sub-lethal doses of drugs can lead to changes in the expression of specific detoxification enzymes and drug resistance development.

Haemonchus contortus, a gastrointestinal parasite of ruminants, is a good model organism for studying drug resistance, as it has evolved resistance to all available anthelmintics over the years.

This study focuses on biotransformation enzymes from short-chain dehydrogenases/reductases (SDR) and aldo-keto reductases (AKR) family in the nematode H. contortus. The constitutive expression of 23 SDRs genes and 22 AKRs was analyzed and compared between drug-susceptible and drug-resistant strains and among various developmental stages (eggs, larvae, adults). Furthermore, the effect of sub-lethal doses of flubendazole, benzimidazole anthelmintic bearing carbonyl group, on the expression of selected genes was evaluated.

The results suggest that SDR/AKR enzymes play different roles during the parasite's life cycle and certain enzymes might be responsible for reductions of xenobiotics, including some anthelmintics.

Anthelmintic (drench) resistance and gastrointestinal nematode (GIN) management is a significant animal health and production limiting concern for New Zealand livestock farmers. Finding useful tools to support GIN management and tackle drench resistance is critical for the sector. A potential approach is targeted selective treatment (TST), aiming to slow the development of drench resistance by reducing total drench used and thus selection pressure for resistant GIN.

Beef + Lamb New Zealand recently funded three case studies to evaluate the use of an existing TST tool, the SmartWorm® application, for use in New Zealand. Three properties in the Hawkes Bay and Wairarapa during 2023 were selected and non-replacement lambs grown out for winter slaughter were used.

SmartWorm®, with an eID tag, leverages liveweight gain, pasture quality and quantity and weather data to identify animals in real time that are most likely to benefit from a dose of drench.

Results showed that across a range of GIN pasture contamination environments, SmartWorm® was able to reduced overall drench input and provided refugia to the farm.

Across the three farms, reduction in drench use of 35%, 53% and 57% with no significant impact on weight gain was recorded. Farmers also recorded overall cost savings.

The objective of this study was to evaluate the effect of anthelmintic drugs on ewe and lamb behaviour. We randomly allocated 60 pregnant ewes to one of three groups (n=20/group): 1) administered moxidectin 2-4 weeks pre-lambing, 2) administered a controlled-release capsule (abamectin and albendazole) 2-4 weeks pre-lambing, and 3) control group. The ewes were housed indoors one month pre-lambing until 1 week post-lambing. Ewe and lamb behaviour was recorded using video-cameras for up to 7 days post-lambing and birth data was recorded. There tended to be a difference between total labour length and ewe treatment (P=0.06). Control ewes were in labour for a median of 65.8 (IQR 33.2 to 139; maximum 420.4). CRC treated ewes were in labour for a median of 67.0 (IQR 55.4 to 159.21; maximum 407.3) minutes. Moxidectin treated ewes were in labour for a median of 47.4 (IQR 30.0 to 106.8; maximum 272.8) minutes. There were no differences between treatments for latencies (from birth) to perform behaviours: lamb to shake head (P=0.68), attempt to stand (P=0.57), complete stand (P=0.7), attempt to suckle (P=0.34) and complete suckle (P=0.84). Although LA drench may not have an affected lamb behaviour, they appear to affect length of labour.

This national study investigated the epidemiology, control and anthelmintic resistance of intestinal nematodes (strongylids and ascarids) in horses using both conventional and advanced molecular techniques. Eighty Thoroughbred farms were recruited for longitudinal and cross-sectional studies, and 86 faecal egg count reduction tests were conducted on 22 farms. Coproscopic and next-generation sequencing techniques were used to determine the worm egg burdens and the types of nematodes, respectively. Questionnaire surveys were distributed to horse breeders and veterinarians to assess worm control practices. Results showed a farm-level prevalence of 100% for strongylid nematodes, with higher rates in younger horses. Only 17% of adult horses were high shedders of strongylid eggs (>500 eggs per gram). Resistance to ivermectin, abamectin, moxidectin, oxfendazole and its combination with pyrantel was found in cyathostomins and Parascaris spp. The most common species identified were species of Cylicocyclus, Cylicostephanus and Coronocyclus. Interval deworming was the most common strategy (≥55%) to control worms, and <40% of breeders performed faecal egg counts. Veterinarians rarely discuss worm control strategies with their clients. The study highlights the high prevalence of nematodes, resistance to common anthelmintics, and suboptimal parasite control practices, emphasising the need for integrated parasite management to improve parasite control in horses.

Fasciola hepatica is a zoonotic parasite of international significance. In Australia, it is the 13^th most important cause of losses to the sheep industry due to its impacts on body condition score, fibre quality and yield. Resistance to the frontline drug, Triclabendazole (TBZ), was first detected in Australia in 1995 and has since spread throughout the world. TBZ is the only drug registered for use against F. hepatica infection in people. With limited chemical control options, and no vaccine available, it is essential that we preserve the efficacy of TBZ.

Recently, livestock producers from the NSW Southern Tablelands have alerted us to their concerns over suspected increases in drug-resistant parasites. We set out to evaluate the prevalence of F. hepatica on ten naturally infected sheep or cattle properties in the region to confirm/deny suspected drug failure. Prior to the commencement of the field trial, we reviewed reports of TBZ resistance in Australia in conjunction with the recent guidelines on evaluating anthelmintic efficacy in ruminants from the World Association for the Advancement of Veterinary Parasitology (WAAVP). Here, we present a critical analysis of the strengths and limitations of these guidelines in light of the practical considerations when working in the field.

Our understanding of anthelmintic resistance in the gastrointestinal nematodes of Australian cattle relies exclusively on small-scale phenotypic reports utilising traditional faecal egg count reduction tests. This approach is not readily scalable to establish the national prevalence of resistance, nor is it conducive of routine longitudinal surveillance for the emergence of resistance in its early stages. This study introduces the benefits of applying mixed amplicon metabarcoding longitudinally for timely and cost-efficient molecular surveillance of multiple anthelmintic resistance mutations, as they emerge on farms. Using opportunistically collected faecal samples from a cattle herd in central west New South Wales (2019–2023), we detected the early emergence of Haemonchus spp. levamisole-resistant S168T shortly after levamisole introduction, while benzimidazole-resistant allele frequencies remained constant. Additionally, we observed the possible spill-over of resistant Haemonchus contortus from sheep, along with variations in faecal burdens and species diversity influenced by climate stochasticity and host immunity. This study emphasises the power of molecular diagnostics for farm-level anthelmintic resistance management, providing essential evidence to support its integration into routine surveillance programmes.