Inconsistency of in vitro exsheathment triggers for gastrointestinal nematode parasites of sheep, cattle and deer.

Exsheathment is crucial in the transition from free-living to parasitic phase for most strongyle nematode species. A greater understanding of this process could help in developing new parasitic control methods. This study aimed to identify commonalities in response to exsheathment triggers (heat acclimation, CO and pH) in a wide range of species (Haemonchus contortus, Trichostrongylus spp.

The distribution of strongylid egg and lungworm (Dictyocaulus eckerti) larval counts in adult female farmed red deer (Cervus elaphus), and the implications for parasite control.

Whilst healthy adult farmed red deer show little clinical indication of parasite infection, they may still be maintaining infection levels on the farm through low-level shedding of nematode eggs and lungworm larvae. This work was undertaken to establish the long-term distribution of parasite counts, to determine whether the higher counts seen in previous trials are repeatable across the same animals. All adult female red deer on a New Zealand North Island property were faecal sampled (n = 209), weighed, and body condition scored (BCS) on five sampling occasions from March - August 2021.

Cross infection of Haemonchus contortus between calves and lambs.

Haemonchus contortus can frequently be found infecting pre-weaned beef calves on sheep and beef farms around the North Island of New Zealand. The purpose of this study was to determine whether parasites cycling in young cattle constitute a potentially important source of infection for sheep. A field isolate of H.

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.

Shortened strongylid egg reappearance periods in horses following macrocyclic lactone administration - The impact on parasite dynamics.

Over the past three decades, equine strongylid egg reappearance periods (ERPs) have shortened substantially for macrocyclic lactone anthelmintics. The ERPs of ivermectin and moxidectin were originally reported in the 8-10 and 12-16 week ranges, respectively, but several recent studies have found them to be around 4-5 weeks for both actives. This loss of several weeks of suppressed strongylid egg output could have substantial implications for parasite control.

Carbohydrate larval antigen (CarLA IgA) responses to mixed species nematode infection in pasture grazed Angora goats.

The genetics of indicator traits for resistance of Angora goats to gastrointestinal nematode parasite infections, and their relationships with productivity traits, were investigated on a commercial mixed-enterprise farm in the eastern North Island of New Zealand. Faecal egg counts (FEC), specific Immunoglobulin A (IgA) and Immunoglobulin G (IgG) antibody titres against carbohydrate larval antigen (CarLA) in saliva, live weight and fleece weights were recorded from 278 goats of 19-20 months of age, run as four separate mobs (breeding bucks, castrated males (wethers), or 2 groups of breeding does). Summary statistics showed the mobs differed significantly in liveweight, log (FEC+50), log (IgA) and log (IgG).

In vitro evaluation of fitness parameters for isolates of Teladorsagia circumcincta resistant and susceptible to multiple anthelmintic classes.

Anthelmintic resistance (AR) is an ever increasing problem for the sheep industry. Several studies worldwide have investigated reversing the trend of increasing AR and documented evidence for reversion toward susceptibility has been found. The hypothesis that resistance mutations compromise parasite fitness was drawn from this evidence.

A model for the development of the free-living stages of Ostertagia leptospicularis, used in conjunction with on-farm egg count data, to estimate sources of pasture contamination on New Zealand red deer (Cervus elaphus) farms.

Farmed red deer face challenges from nematode parasites, primarily the pulmonary species Dictyocaulus eckerti and the complex of Ostertagiinae nematodes in the abomasum. Previous investigations on New Zealand deer farms identified limited seasonality in faecal egg and larval output in all stock classes, however, this does not indicate the key times of year those eggs develop into infective-stage larvae, and subsequently contribute to infection risk. A simple temperature-driven model was developed for the free-living stages of a representative deer-specific Ostertagiinae species; Ostertagia leptospicularis.

The production costs of Haemonchus contortus and other nematode parasites in pre-weaned beef calves in New Zealand.

Haemonchus contortus can frequently be found infecting pre-weaned beef calves on sheep and beef farms around the North Island of New Zealand. The purpose of this study was to consider whether the presence of this parasite alone, or as part of a mixed infection, could be impacting growth rates of young animals, on three commercial farms in the North Island of New Zealand. Trials were conducted on commercial sheep and beef farms in each of the Northland, King Country and Gisborne regions, in late summer/autumn (February to April) of 2016 to measure the effect of treatment with narrow and broad spectrum anthelmintics on liveweight gain of spring-born calves pre-weaning.

Seasonal output of gastrointestinal nematode eggs and lungworm larvae in farmed wapiti and red deer of New Zealand.

Gastrointestinal nematode parasites and lungworm are significant animal health issues for farmed wapiti and red deer (Cervus elaphus). Chronic infection with gastrointestinal nematodes, coupled with sporadic, often pathogenic, outbreaks of the lungworm Dictyocaulus eckerti in young deer has resulted in many farmers relying heavily on anthelmintic treatments. An improved understanding of the epidemiology of the parasites infecting farmed deer, including the sources and seasonality of pasture contamination on the farm, is essential to the development of more integrated and sustainable control programs.

A journey through 50 years of research relevant to the control of gastrointestinal nematodes in ruminant livestock and thoughts on future directions.

This review article provides an historical perspective on some of the major research advances of relevance to ruminant livestock gastrointestinal nematode control over the last 50 years. Over this period, gastrointestinal nematode control has been dominated by the use of broad-spectrum anthelmintic drugs. Whilst this has provided unprecedented levels of successful control for many years, this approach has been gradually breaking down for more than two decades and is increasingly unsustainable which is due, at least in part, to the emergence of anthelmintic drug resistance and a number of other factors discussed in this article.

Three-year study to evaluate an anthelmintic treatment regimen with reduced treatment frequency in horses on two study sites in Belgium.

In the present study, an anthelmintic treatment regimen with reduced treatment frequency was evaluated in horses on two study sites in Belgium during three consecutive summer pasture seasons. Historically, the horses on both study sites were treated up to 6 times a year with ivermectin (IVM) or up to 4 times a year with moxidectin (MOX), and previous efficacy evaluations indicated a reduced egg reappearance period in some of the treated horses for both IVM (28 days) and MOX (42 days). In the present study, all horses were treated with IVM or MOX in the spring and in autumn.

Route of administration affects the efficacy of moxidectin against Ostertagiinae nematodes in farmed red deer (Cervus elaphus).

The influence of route of administration on the pharmacokinetics and efficacy of macrocyclic lactone anthelmintics has been a subject of interest due to its potential to influence the development of anthelmintic resistance. For most parasite species studied so far, oral administration results in the highest concentrations of drug in the parasites and the highest efficacy against resistant genotypes. However, a recent study in cattle measured the highest levels of ivermectin in the abomasal Ostertagia ostertagi following subcutaneous injection, but it was not possible to correlate these elevated levels with efficacy.

Host effects on the free-living stages of Haemonchus contortus.

A group of 5 lambs (Host 1-5) was infected with the same batch of Haemonchus contortus and after patency individual faecal samples were collected, separately incubated at 23 °C for 14 days and third stage larvae collected through Baermannisation. Life-history traits were compared between larvae from different hosts: the length of the larvae was measured by microscope image analysis, larval survival in water at 35 °C, larval susceptibility to ivermectin (EC) in a migration assay, the proportion of larvae exsheathing in vitro and the proportion establishing to the adult stage in young lambs. For all traits there were significant differences between the host animals, with larvae from specific hosts following a consistent pattern of displaying the highest or lowest trait results.

Effects of long-acting, broad spectra anthelmintic treatments on the rumen microbial community compositions of grazing sheep.

Anthelmintic treatment of adult ewes is widely practiced to remove parasite burdens in the expectation of increased ruminant productivity. However, the broad activity spectra of many anthelmintic compounds raises the possibility of impacts on the rumen microbiota. To investigate this, 300 grazing ewes were allocated to treatment groups that included a 100-day controlled release capsule (CRC) containing albendazole and abamectin, a long-acting moxidectin injection (LAI), and a non-treated control group (CON).

Route of administration influences the concentration of ivermectin reaching nematode parasites in the gastrointestinal tract of cattle.

An animal trial was conducted to measure the concentrations of ivermectin occurring in abomasal and small intestinal contents and mucosa, and in the target parasites (Ostertagia ostertagi and Cooperia oncophora) following administration by subcutaneous, oral and pour-on routes. Twenty-five steers were infected with ivermectin-resistant isolates of O. ostertagi and C.

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.

Climate change is likely to increase the development rate of anthelmintic resistance in equine cyathostomins in New Zealand.

Climate change is likely to influence livestock production by increasing the prevalence of diseases, including parasites. The traditional practice of controlling nematodes in livestock by the application of anthelmintics is, however, increasingly compromised by the development of resistance to these drugs in parasite populations. This study used a previously developed simulation model of the entire equine cyathostomin lifecycle to investigate the effect a changing climate would have on the development of anthelmintic resistance.

Dealing with double trouble: Combination deworming against double-drug resistant cyathostomins.

An alternative control regimen for drug-resistant parasites is combination deworming, where two drugs with different modes of action are administered simultaneously to target the same parasite. Few studies have investigated this in equine cyathostomins. We previously reported that an oxibendazole (OBZ) and pyrantel pamoate (PYR) combination was not sustainable against a cyathostomin population with high levels of OBZ and PYR resistance.

Managing anthelmintic resistance in cyathostomin parasites: Investigating the benefits of refugia-based strategies.

Selective anthelmintic therapy has been recommended as a sustainable strategy for cyathostomin control in horse populations for several decades. The traditional approach has been to determine strongyle fecal egg counts (FEC) for all horses, with treatment only recommended for those exceeding a predetermined threshold. The aims are to achieve a reduction of overall egg shedding, while leaving a proportion of the herd untreated, which lowers anthelmintic treatment intensity and reduces selection pressure for development of anthelmintic resistance.

The complete mitochondrial genome of the New Zealand parasitic roundworm (Trichostrongyloidea: Haemonchidae) field strain NZ_Teci_NP.

The complete mitochondrial genome of the New Zealand parasitic nematode field strain NZ_Teci_NP was sequenced and annotated. The 14,083 bp-long mitogenome contains 12 protein-coding genes (atp8 gene missing), two ribosomal RNAs (rRNAs), and 22 transfer RNAs (tRNAs). Phylogenetic analysis showed that NZ_Teci_NP forms a monophyletic cluster with the remaining Haemonchidae species and further reinforces the high levels of diversity and gene flow observed among Trichostrongylidae.

The complete mitochondrial genome of the New Zealand parasitic roundworm (Trichostrongyloidea: Haemonchidae) field strain NZ_Hco_NP.

The complete mitochondrial genome of the New Zealand parasitic nematode field strain NZ_Hco_NP was sequenced and annotated. The 14,001 bp-long mitogenome contains 12 protein-coding genes (atp8 gene missing), two ribosomal RNAs, 22 transfer RNAs, and a 583 bp non-coding region. Phylogenetic analysis showed that NZ_Hco_NP forms a monophyletic cluster with the remaining three Haemonchidae species, and further illustrates the high levels of diversity and gene flow among Trichostrongylidae.

The Genome Sequence of the Anthelmintic-Susceptible New Zealand Haemonchus contortus.

Internal parasitic nematodes are a global animal health issue causing drastic losses in livestock. Here, we report a H. contortus representative draft genome to serve as a genetic resource to the scientific community and support future experimental research of molecular mechanisms in related parasites.

The effect of climate, season, and treatment intensity on anthelmintic resistance in cyathostomins: A modelling exercise.

Anthelmintic resistance is widespread in equine cyathostomin populations across the world, and with no new anthelmintic drug classes in the pharmaceutical pipeline, the equine industry is forced to abandon traditional parasite control regimens. Current recommendations aim at reducing treatment intensity and identifying high strongylid egg shedders in a targeted treatment approach. But, virtually nothing is known about the effectiveness of these recommendations, nor their applicability to different climatic regions, making it challenging to tailor sustainable recommendations for equine parasite control.

Modelling the development of anthelmintic resistance in cyathostomin parasites: The importance of genetic and fitness parameters.

Previously described models for the free-living and parasitic phases of the cyathostomin life-cycle were combined into a single model for the complete life-cycle. The model simulates a single free-living population on pasture utilising parasite egg output from the horses and localised temperature and rainfall data to estimate infective larval density on herbage. Multiple horses of different ages are possible, each with an individualised anthelmintic treatment programme.