Evaluation of changes in drug susceptibility and population genetic structure in Haemonchus contortus following worm replacement as a means to reverse the impact of multiple-anthelmintic resistance on a sheep farm

Worm replacement with susceptible Haemonchus contortus benefits weight gain, reduces anthelmintic treatments and impacts sheep breeds differently

This study evaluated the effect of partial and total replacement of Haemonchus contortus in sheep breeds. Pregnant ewes of White Dorper (DO), Santa Inês (SI) and Texel (TX) breeds were allocated into three groups: Control (C), Partial Replacement (PR) and Total Replacement (TR). PR and TR ewes received anthelmintics (AH), were artificially infected with H. contortus-susceptible isolate and grazed on resistant-infested or worm-free paddocks, respectively. Control animals were untreated and naturally infected. 106 lambs were born and kept in the paddocks of their respective mothers. Their egg count per gram of feces (FEC) and packed cell volume (PCV) were recorded every 21 days, until 189 days old. Fecal Egg Count Reduction Test revealed AH efficacy of 85 %, 92 % and 97 % in the C, PR and TR groups, respectively, for ewes and 60 %, 74 % and 98 %, respectively, for lambs at day 147. SI animals (p < 0.001) received fewer AH treatments and presented a higher PCV than DO and TX, reaching similar weight gain to the other breeds. Male lambs (p < 0.001) presented a higher FEC, lower PCV and lower frequency of Famacha score 1. Higher age at weaning resulted in a lower FEC (p = 0.0073), higher PCV (p = 0.002), and higher frequencies of Famacha 1 and body condition scores 3 and 4. AH treatment was more efficient after worm replacement, reducing FEC (p < 0.001) and favoring weight gain in the PR and TR groups. Avoiding early weaning, adopting selective AH treatments and using more resistant sheep breeds may delay the reestablishment of resistance after worm replacement.

Gastrointestinal nematode parasites of grazing ruminants: a comprehensive literature review of diagnostic methods for quantifying parasitism, larval differentiation and measuring anthelmintic resistance

This review summarises up-to-date research on the diagnosis of gastrointestinal nematode (GIN) infection in livestock and anthelmintic resistance in GIN. It was commissioned to assist funding bodies to prioritise and guide research and extension efforts to improve the health, welfare and productivity of grazing ruminants in the face of challenge with GIN. A comprehensive review of published articles from journals, books and websites was undertaken, with a focus on peer-reviewed articles published between 2000 and 2024 involving genera of GIN in grazing sheep and cattle with economic importance to New Zealand. Suggestions for articles to include were received from 14 experts in GIN diagnostics. This review is a summary of a longer report submitted to the sponsoring organisation. Clinical signs of GIN infection in grazing ruminants in temperate grazing systems are inadequate as triggers for management interventions including anthelmintic treatment as they are visible only after economically significant pathological changes have occurred. Livestock producers benefit from monitoring GIN burdens using faecal egg counts (FEC) or associated signals such as weight gain. In future, they may use remote monitoring devices for activity in animals, as well as estimating pasture larval contamination. Methods of diagnosing GIN infections using automated FEC devices have improved the convenience of monitoring parasite burdens compared with traditional laboratory methods. However, a lack of quality control measures and a gap in training of skilled technicians for larval differentiation may lead to a shortage of diagnostic capability. Current methods of diagnosing anthelmintic resistance, particularly FEC reduction tests, are not likely to be replaced by laboratory assays in the near future and attention should be focused on facilitating application of new FEC technologies for both animal monitoring and resistance diagnosis. Extension and application of currently available methods and technology will improve animal health and productivity in ruminant grazing systems in the short term. Adoption of novel technologies for remote animal monitoring, practical tools for estimating pasture larval contamination and promoting genetic selection for immunity and resilience to GIN in both sheep and cattle will further enhance productivity in the long term.

Evaluation of a combination of Citrus aurantium var. Dulcis essential oil and albendazole for the treatment of sheep gastrointestinal nematodes

Citrus fruits are consumed all over the world and their by-products are used for animal feed and essential oils production. This study aimed to evaluate the in vitro and in vivo activity of Citrus aurantium var. Dulcis essential oil (CaEO) combined with ABZ against benzimidazole resistant Haemonchus contortus. In vitro egg hatching assays (EHA) were performed using CaEO and ABZ to estimate the effective concentration to achieve 50% egg death (EC₅₀) values and calculate the test essential oil and drug combinations using a simplex-centroid mixture design. These concentrations were used for a second round of EHAs. Sixteen sheep were randomly allocated into two groups and treated with ABZ and the combination of CaEO and ABZ, and faecal egg count reduction tests were performed. In the first round of EHA, CaEO and ABZ showed EC₅₀ values of 0.57 and 0.0048 mg mL^-1, respectively. The H. contortus strain used in the study was shown to be highly benzimidazole resistant, with only 1.5% of parasites having susceptible ß-tubulin SNP genotypes. The ABZ reduced the shedding of nematode eggs by 78%, however, its combination with CaEO reduced faecal egg counts by only 9%. The present study is important to highlight the interferences of natural products in anthelmintic metabolism and consequently in drug efficacy.

Economic impact of gastrointestinal nematodes in Morada Nova sheep in Brazil

This study evaluated the economic impact of gastrointestinal nematode (GIN) infection in Morada Nova lambs under different parasite chemical control conditions. For this, 246 lambs, in the rainy and dry season, were randomized into groups according to their anthelmintic treatment with levamisole: control (CT: no treatment); routine treatment (RT: treated every 42 days); and targeted selective treatment (TST: treated according to the average daily weight gain, DWG). From 63 days of age (D63) to D210, the lambs were weighed and monitored for GIN infection parameters. Spending on anthelmintics in the production system was 1.3% of the total economic result. The economic result per animal (R$ 5.00 = US$ 1.00) was higher in the RT group, amounting to US$ 6.60 in the rainy and US$ 5.69 in the dry season, due to higher DWG. Thus, RT presented economic results 14.4% and 10.9% higher than CT, and 7.2% and 1.9% higher than TST, in the rainy and dry season, respectively. However, fast development of resistance made RT unfeasible. Here, the economic impact of GIN infection on a national scale is discussed, demonstrating its importance and the impossibility of profitable and sustainable sheep production without adequate control.

Single-Nucleotide Polymorphisms in the Beta-Tubulin Gene and Its Relationship with Treatment Response to Albendazole in Human Soil-Transmitted Helminths in Southern Mozambique

Soil-transmitted helminth (STH) cornerstone control strategy is mass drug administration (MDA) with benzimidazoles. However, MDA might contribute to selection pressure for anthelmintic resistance, as occurred in livestock. The aim of this study is to evaluate the treatment response to albendazole and the relationship with the presence of putative benzimidazole resistance single-nucleotide polymorphisms (SNPs) in the β-tubulin gene of STH in Southern Mozambique. After screening 819 participants, we conducted a cohort study with 184 participants infected with STH in Manhiça district, Southern Mozambique. A pretreatment and a posttreatment stool samples were collected and the STH infection was identified by duplicate Kato-Katz and quantitative polymerase chain reaction (qPCR). Cure rate and egg reduction rates were calculated. Putative benzimidazole resistance SNPs (F167Y, F200T, and E198A) in Trichuris trichiura and Necator americanus were assessed by pyrosequencing. Cure rates by duplicate Kato-Katz and by qPCR were 95.8% and 93.6% for Ascaris lumbricoides, 28% and 7.8% for T. trichiura, and 88.9% and 56.7% for N. americanus. Egg reduction rate by duplicate Kato-Katz was 85.4% for A. lumbricoides, 34.9% for T. trichiura, and 40.5% for N. americanus. Putative benzimidazole resistance SNPs in the β-tubulin gene were detected in T. trichiura (23%) and N. americanus (21%) infected participants at pretreatment. No statistical difference was observed between pretreatment and posttreatment frequencies for none of the SNPs. Although treatment response to albendazole was low, particularly in T. trichiura, the putative benzimidazole resistance SNPs were not higher after treatment in the population studied. New insights are needed for a better understanding and monitoring of human anthelmintic resistance.

Population replacement of benzimidazole-resistant Haemonchus contortus with susceptible strains: evidence of changes in the resistance status

The spread of anthelmintic resistance (AR) in nematode populations threatens the viability of sheep production systems worldwide, and warrants the adoption of sensitive, practical, and standardized tests to detect AR. The aim of this study was to characterize the replacement of an Haemonchus contortus population resistant to benzimidazoles (BZDs) by a susceptible one, by means of both phenotypic and genotypic techniques. Phenotypic methods to assess BZD resistance included in vivo tests, such as the fecal egg count reduction test (FECRT), and in vitro tests, such as the egg hatch assay (EHA). Additionally, genotypification of polymorphisms associated with BZD resistance by sequencing a fragment of the isotype 1 β-tubulin gene was carried out. The initial, BZD-resistant population (initial Balcarce population) exhibited an egg count reduction (ECR) of 59.3%. Following refugium replacement, the final population (final Balcarce population) exhibited an ECR of 95.2%. For the initial Balcarce population, the median effective dose (ED₅₀) for the EHA was 0.607 μg thiabendazole (TBZ)/mL, with a rate of eclosion at a discriminating dose (E_DD) of 0.1 μg TBZ/mL of 76.73%. For the final Balcarce population, ED₅₀ was 0.02 μg TBZ/mL, and E_DD was 1.97%. In the initial population, 93% of the analyzed individuals exhibited genotypic combinations associated with BZD resistance (53% Phe/Phe₁₆₇-Tyr/Tyr₂₀₀, 37% Phe/Tyr₁₆₇-Phe/Tyr₂₀₀, and 3% Phe/Tyr₁₆₇-Glu/Leu₁₉₈). Conversely, no combination associated with resistance was found in individuals from the final population. All of the tests were useful for detecting AR to BZDs. The results from the genetic and phenotypical studies were consistent, and the resulting information greatly aided in interpreting the outcomes of the population replacement and the potential impact of this strategy on management of AR.

Worms and bugs of the gut: the search for diagnostic signatures using barcoding, and metagenomics-metabolomics

Gastrointestinal (GI) helminth infections cause significant morbidity in both humans and animals worldwide. Specific and sensitive diagnosis is central to the surveillance of such infections and to determine the effectiveness of treatment strategies used to control them. In this article, we: (i) assess the strengths and limitations of existing methods applied to the diagnosis of GI helminth infections of humans and livestock; (ii) examine high-throughput sequencing approaches, such as targeted molecular barcoding and shotgun sequencing, as tools to define the taxonomic composition of helminth infections; and (iii) discuss the current understanding of the interactions between helminths and microbiota in the host gut. Stool-based diagnostics are likely to serve as an important tool well into the future; improved diagnostics of helminths and their environment in the gut may assist the identification of biomarkers with the potential to define the health/disease status of individuals and populations, and to identify existing or emerging anthelmintic resistance.

Preparation of Eprinomectin Nanoemulsions and Determination of Their Pharmacokinetics and Pharmacodynamics in Dairy Cows

This study aimed to develop an anthelmintic that leaves no residues and is safe and efficient for use in cows. We constructed classical pseudoternary phase diagrams using experimental animal data to optimize and characterize the eprinomectin nanoemulsion formulas. The emulsion samples prepared with ethyl acetate, polysorbate 80, and 1-propanediol as the main components were transparent and uniform when observed under a Hitachi transmission electron microscope (TEM) system. A Mastersizer 3000 laser particle size analyzer was used to determine the particle sizes of the prepared nanoemulsions. The nanoemulsions were homogeneously dispersed, with an average particle size of 12.61 nm and a polydispersity index of (PDI) 0.297. High-performance liquid chromatography confirmed no statistically significant changes in the samples after 24 months at 4 °C, 25 °C, and 37 °C; the samples exhibited long-term stability. The PK/PD studies confirmed that the injection of eprinomectin nanoemulsions at a dose of 0.2 mg/kg body weight was effective, with a withdrawal period of 0 days for dairy cows. The total extermination rate of the nanoemulsions against adult nematodes was 98.40±1.52%. The AUC_milk/plasma ratio was 0.67±0.03. The optimal dose was found to be 0.2 mg/kg body weight.

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. We first cover the remarkable success story of the discovery and development of broad-spectrum anthelmintic drugs, the changing face of anthelmintic drug discovery research and the emergence of anthelmintic resistance. This is followed by a review of some of the major advances in the increasingly important area of non-pharmaceutical gastrointestinal nematode control including immunology and vaccine development, epidemiological modelling and some of the alternative control strategies such as breeding for host resistance, refugia-based methods and biological control. The last 50 years have witnessed remarkable innovation and success in research aiming to improve ruminant livestock gastrointestinal nematode control, particularly given the relatively small size of the research community and limited funding. In spite of this, the growing global demand for livestock products, together with the need to maximise production efficiencies, reduce environmental impacts and safeguard animal welfare - as well as specific challenges such as anthelmintic drug resistance and climate change- mean that gastrointestinal nematode researchers will need to be as innovative in the next 50 years as in the last.

What makes a good fecal egg count technique?

The first parasite fecal egg counting techniques were described over 100 years ago, and fecal egg counting remains essential in parasitology research as well as in clinical practice today. Several novel techniques have been introduced and validated in recent years, but this work has also highlighted several current issues in this research field. There is a lack of consensus on which diagnostic parameters to evaluate and how to properly design studies doing so. Furthermore, there is a confusing and sometimes incorrect use of terminology describing performance of fecal egg counting techniques, and it would be helpful to address these. This manuscript reviews qualitative and quantitative diagnostic performance parameters, discusses their relevance for fecal egg counting techniques, and highlights some of the challenges with determining them. Qualitative parameters such as diagnostic sensitivity and specificity may be considered classic diagnostic performance metrics, but they generally only have implications at low egg count levels. The detection limit of a given technique is often referred to as the "analytical sensitivity", but this is misleading as the detection limit is a theoretically derived number, whereas analytical sensitivity is determined experimentally. Thus, the detection limit is not a diagnostic performance parameter and does not inform on the diagnostic sensitivity of a technique. Quantitative performance parameters such as accuracy and precision are highly relevant for describing the performance of fecal egg counting techniques, and precision is arguably the more important of the two. An absolute determination of accuracy can only be achieved by use of samples spiked with known quantities of parasite ova, but spiking does not necessarily mimic the true distribution of eggs within a sample, and accuracy estimates are difficult to reproduce between laboratories. Instead, analysis of samples from naturally infected animals can be used to achieve a relative ranking of techniques according to egg count magnitude. Precision can be estimated in a number of different approaches, but it is important to ensure a relevant representation of egg count levels in the study sample set, as low egg counts tend to associate with lower precision estimates. Coefficients of variation generally provide meaningful measures of precision that are independent of the multiplication factor of the techniques evaluated. Taken together, there is a need for clear guidelines for studies validating fecal egg counting techniques in veterinary parasitology with emphasis on what should be evaluated, how studies could be designed, and how to appropriately analyze the data. Furthermore, there is a clear need for better consensus regarding use of terminology describing the diagnostic performance of fecal egg count techniques.